low vision manual-0750618159

© 2007, Elsevier Limited. All rights reserved.First published 2007

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ISBN-13: 978-07506-1815-1ISBN-10: 0-7506-1815-9

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Foreword

It may seem paradoxical, but visual impairment and the need for its rehabilitation are becoming more important because of improving health care. Worldwide, longevity is increasing. Having a larger proportion of the population in the older age groups means a higher prevalence of visual impairment because vision loss predominantly results from age-related diseases and disor-ders. As new or improved treatments are developed for various disabling eye diseases, there will inevitably be some shifts in the relative importance of different eye diseases, but for the foresee-able future, we can expect the incidence of age-related vision loss to continue to rise. Low vision care will continue to become increasingly important.

The goal of low vision rehabilitation is to minimise any func-tional impediments imposed by vision loss. In part, this is done by gaining as much use as possible from the patient’s remaining visual abilities. In this process, the ophthalmic clinician’s fi rst task is to identify and understand the functional diffi culties that the individual experiences as a direct or indirect result of their visual limitations. Tasks associated with reading, face recognition and mobility are likely to remain around the top of the list. Second, the clinician seeks a more detailed assessment of the individual’s vision through examining the eyes in order to better understand the causative pathology and the prognosis, evaluating the refrac-tive characteristics of the eyes, and performing a range of tests of visual function. Visual acuity, visual fi elds, contrast sensitivity,

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colour vision, light and dark adaptation, oculo-motor control and glare disability are all relevant and clinically-quantifi able visual functions. However, it is not enough to simply measure thresholds. Clinicians should also evaluate the ease, effi ciency and accuracy of task performance, and dependencies on more subtle variation in the visual stimulus, such as lighting levels and visual clutter. As the third part of the process, the ophthalmic clinician’s job is to consider ways in which the performance of the patient’s visual tasks can be optimised or facilitated though optical manipulations by magnifi cation, minifi cation, prisms, fi lters, lighting control and through the use of electronic display systems or through training specifi c visual skills.

Taking care of the visual aspects of the patient’s tasks is only part of the overall rehabilitation process for the visually impaired patient. Accessing other rehabilitative services and support can be crucial. Rehabilitation specialists, mobility instructors, occupa-tional and physical therapists, special educators and social workers are all important parts of the team of rehabilitation professionals that can provide strategies, techniques and training for improving task performance, or facilitating the use of devices that can make some tasks less dependent on vision. Often the psychological, social and recreational needs of visually impaired individuals warrant considerable attention and support from family, friends and, sometimes, professionals. For many, especially those who acquire their vision loss in adult life, there will be a need for voca-tional counselling and training, along with accommodations being made in the workplace environment.

Technological developments are presenting exciting new oppor-tunities but also new challenges for low vision rehabilitation. In particular, display technologies are allowing a lot more scope for optimising the display of printed material to our visually impaired patients. Electronic display systems offer much more fl exibility than the more traditional optical low vision aids. Most video-magnifi ers allow easy variations in print size, contrast, luminance and colour of the printed or pictorial displays. The same set of visual parameters can be varied on computer-controlled display screens, but computerisation expands the range of modifi cations of the visual display through reformatting by changing font, style, columns, rows, spacing, highlighting, controlled scrolling, stream-ing, and other modes of visual presentation. Computers can also enable the information to be displayed as speech output or tactile output that may be used to supplement or replace the usual visual

Foreword

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ix

screen images. In most societies, the information technology revo-lution is changing the visual demands of daily life. Mobile phones, automatic bank telling machines and similar displays for business transactions are becoming more commonly encountered by people from all walks of life. In Western societies at least, personal com-puters are becoming more important to individuals as the favoured means of communicating with friends, paying bills, checking bank and business records, as well as using the web-based tech-nologies to access information for a wide variety of recreational, occupational, spiritual and intellectual purposes. Despite their diffi culties in acquiring skills to use a keyboard or a mouse, the elderly are rapidly expanding their use of computers. In the least technologically-developed countries, there is currently an expo-nential increase in the use of mobile phones and the associated expansion of access to information technology through both visual and auditory displays.

With many of these electronically-controlled displays, there is scope for the user to experiment and make their own choices of display parameters. However, because ophthalmic clinicians understand eye diseases and their effects on vision, and they know how the visual system works and how visual images and displays may be manipulated, these practitioners should be able to provide well-informed advice and guidance on the selection of the display parameters, and on which methods and strategies are best for the individual. Whether the displayed image comes from an optical system or a display screen, the skills of ophthalmic cli nicians are needed to provide the optical corrections so often required to ensure that the retinal image is in satisfactory focus.

Only a relatively small fraction of optometrists and ophthalmolo-gists are specialising in low vision rehabilitation, maintaining a high level of expertise, and developing close working associ-ations with other low vision rehabilitation specialists. Fewer still are active in research into relationships between functional per-formance, visual functions and quality of life, or in the develop-ment of improved methods for assessing visual functions or methods for training visual skills, or in creating new optical and electronic systems to assist visually impaired patients. But it is not just the experts who need to know about low vision rehabilitation. All optometrists and ophthalmologists engaged in clinical practice have a responsibility to be informed about low vision rehabilita-tion and what it can do. All eye-care practitioners need to be knowledgeable about today’s newly emerging pharmacological,

Foreword

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surgical and genetic treatments that hold promise for reducing the occurrence or severity of certain eye diseases. They need to be able to answer their patients’ questions on such matters, and to make appropriate referrals. As society’s experts in vision, all optome-trists and ophthalmologists have a similar responsibility to be knowledgeable about methods for assessing functional vision, and the possibilities of patients benefi ting from the use of the various optical and electronic low vision aids. As part of a healthcare delivery system, they all have a responsibility to be acquainted with the range of rehabilitation services and support systems that are available to visually impaired persons.

This Low Vision Manual presents a technically sound, compre-hensive and up-to-date account of low vision rehabilitation that will serve as an excellent guide and resource for students and clinicians wishing to develop their knowledge and skills in low vision care. For those who simply wish to familiarise themselves with the state of the art in low vision care today, this Manual will be an accessible and valuable source of information. For clinicians who are already expert, this Low Vision Manual will provide new information and new insights from its knowledgeable team of authors.

Ian L. Bailey

Foreword

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Preface

The population is ageing, particularly in ‘developed’ nations. This, together with the lack of treatment options for conditions such as atrophic age-related macular degeneration, has resulted in a sub-stantial increase in the number of visually impaired people requir-ing ‘vision care’. In addition, as our standard of living rises, there is an expectation that we will maintain a high quality of life into old age. These two factors continue to create an ever increasing demand on low vision rehabilitation services, especially those that involve multidisciplinary integrated care.

This book has been written by clinical and research experts in the fi elds of disease detection and management, primary and sec-ondary optometric care, low vision optics and prescribing, coun-selling and rehabilitation. In writing this text we have attempted to disseminate the latest research fi ndings in a digestible format for the clinician. The book is intended to be a comprehensive guide and up-to-date reference source. It is presented in an easy to access format, which should enable the front-line eye care professional to provide patients with sound, research-based, clinical care and rehabilitation. It is unique in presenting both the latest evidence-based knowledge and in covering the full gamut of issues relevant to comprehensive low vision rehabilitation.

In Section 1, low vision and its epidemiology are defi ned. The signs, symptoms and clinical management of the range of condi-tions that cause visual impairment in the three stages of life – childhood, working age and advancing years – are presented in

xi

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detail. The measurement of visual function of the visually impaired is covered in Section 2, not just in terms of traditional measures such as visual acuity and contrast sensitivity, but importantly in considering the psychology of visual loss and functional visual measures such as quality of life. In Section 3, low vision aids, from simple hand magnifi ers to electronic vision enhancement systems, are described from their optics to practical tips on prescribing. Last, but by no means least, rehabilitation strategies and tech-niques are discussed in Section 4, embracing the treatment of the visually impaired as a whole person. This book aims to be an essential read and reference text for all professionals involved in the care of the visually impaired, including ophthalmologists, optometrists, dispensing opticians, orthoptists, ophthalmic nurses, rehabilitation workers, occupational therapists, social workers, peer workers and psychologists, to name but a few. Although the book mentions, where appropriate, the situation in the UK, it also covers the worldwide status, and the contents should prove valu-able to those wishing to push back the frontiers of the fi eld, irre-spective of location.

We hope that this book will be of use in routine eye care practice to enhance patient care from diagnosis to rehabilitation and, in par-ticular, to optimise the quality of life of visually impaired people.

James S WolffsohnA Jonathan Jackson

Dedication

Collectively, we would wish to dedicate this book to those who have come along to see us as patients, or indeed as the parents or guardians of our ‘smaller’ patients, and who have placed their trust in us to help and advise on the optometric, medical and rehabilitative management of visual impairment. To our many visually impaired friends we would wish to express our genuine thanks for all that you have taught us over the years.

Jonathan, James, Giuliana and Owen

Acknowledgements

This text, which has been a labour of love over many years, could not have evolved to this point had it not been for the long suffering

Preface

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Preface

xiii

support of Carolyn, Rachel, Gordon and Pauline, our respective wives and husband. Their support, and sacrifi ce, is very much appreciated, as too is that of our children, Daniel, Lauren, Joshua, Peter, Laura and Adam. We would also wish to acknowledge the support of clinical colleagues at the Royal Victoria Hospital and, in particular, the secretarial support of Miss Elizabeth Elliman and Ms Amanda Macfarlane. Our thanks also go to the members of the Photographic Team at the RVH and QUB, Mr Mark Tierney, Mr David McCallum, Ms Stephanie O’Connor and Mr Vittorio Silvestri and to our many friends and colleagues from GDBA and RNIB who have assisted with many of the illustrations. Finally, we would wish to thank Ms Barbara Ryan for having reviewed the text and providing helpful suggestions concerning layout and content.

Prof AJ Jackson, Dr JS Wolffsohn, Dr G Silvestri, Mr OF Adams

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xiv

Editors

Dr Jonathan Jackson studied Ophthalmic Optics/Optometry at Glasgow College of Technology (UK), achieving a 1st class Honours Degree (1981). Upon completion of a pre-registration year at Moorfi elds Eye Hospi-tal, London he obtained membership of the College of Optometrists and was awarded both the Scottish and Colebrook prizes (1982). After returning to Belfast to establish a hospi-tal optometry department at the Royal Victo-

ria Hospital, he completed a PhD entitled ‘An Analysis of Corneal Endothelial Morphology under Normal and Traumatic Conditions’ at Queen’s University (1993). He is currently Principal Optometrist at the Royal Victoria Hospital and is Head of Professional Ophthal-mic Services at the Northern Ireland Central Services Agency.

Professor Jackson holds an Honorary Senior Lectureship in the School of Biomedical Sciences/Centre for Vision Science, Queen’s University and a visiting Professorship at the Department of Optometry, University of Ulster, Coleraine. His research interests include visual disability and corneal physiology/contact lenses with particular emphasis on paediatrics and learning disability.

Professor Jackson has contributed to, as either principal or senior author, in excess of 60 peer reviewed scientifi c papers and has presented research fi ndings at a broad range of national and international multidisciplinary meetings. The Belfast visual impairment team which he leads holds a large number of research grants from national and regional funders.

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xv

Editors

Dr James Wolffsohn studied optometry at UMIST, Manchester, UK, achieving a 1st class degree. He qualifi ed to practice independently following a pre-registration year at Moorfi eld’s Eye Hospital, London. Following this, James undertook a PhD on ‘the effects of visual imagery on the oculomotor system’ at Cardiff University and funded by British Aerospace. He then took up a clinical/ research position at the Victorian College of Optometry/Uni-versity of Melbourne, Australia in 1997. In

2000, he returned to the UK and a lectureship at Aston University, being promoted to Senior Lecturer in 2002 and Reader in 2006. He is now Head of Optometry. James’ research and teaching interests mainly revolve around contact lenses, low vision and the measure-ment of accommodation, having published over 65 peer reviewed academic papers and given numerous international presentations. James is also the past President of the British Contact Lens Association.

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Contributors

Owen F Adams MA Cert in Technical Work for the BlindLow Vision Consultant, Downpatrick, UK

Nicholas J Rumney MScOptom FCOptom FAAOBishop, Bishop & Rumney, Hereford, UK

Janet Silver OBE, DSc, FCOptomLondon, UK

Giuliana Silvestri MD FRCS FRCP(Ed) FRCOphthSenior Lecturer & Consultant Ophthalmic Surgeon, Head of Division of Surgery & Perioperative Care, Department of Ophthalmology, Queen’s University Belfast, Royal Victoria Hospital, Belfast, UK

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Plates 1 & 2 (Fig. 2.2) Example of a ‘fl ecked’ retina. Both colour plates show fundus fl avimaculatus at different stages of the disease. Plate 1, Early changes with well defi ned yellow ‘fi sh-tail’-like fl ecks and mild macular atrophy. Visual acuity is relatively well preserved at this stage. Plate 2, More advanced stage of the disease, with signifi cant macular atrophy.

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Plates 3 & 4 (Fig. 2.4) Advanced retinitis pigmentosa with extensive retinal pigmentary changes, vascular attenuation and optic disc pallor. Plate 3, right eye, Plate 4, left eye.

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Plates 5 & 6 (Fig. 3.1) Treated diabetic retinopathy in a 24-year-old woman. The patient has been treated with panretinal photocoagulation for proliferative retinopathy (scars in the peripheral retina of the left eye – Plate 6) and with bilateral grid laser for maculopathy (subtle scars in the macular areas – Plates 5 & 6).

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Plates 7 & 8 (Fig. 4.5) Anterior segment view of an intraocular miniaturised telescope (IMT) implanted within the capsular bag (Plate 7) with corresponding view through the implant of the retina showing a disciform scar (Plate 8).

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Plate 9 (Fig. 6.2) Corneal topographical maps illustrating the difference between regular with-the-rule astigmatism (upper panel) and keratoconus (lower panel). The steep, inferiorally positioned, cone in the lower panel gives rise to a distorted scissor-like retinoscopy refl ex, irregular astigmatism and a progressively increasing myopic refractive correction.

Plate 10 (Fig. 7.4) The Thomson Test Chart 2000 computer-generated visual acuity assessment system. (Courtesy of Professor D Thomson; reproduced with permission from Macnaughton 2005.)

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Plate 11 (Fig. 7.11B) Accurate positioning of targets by the Nidek MP1 microperimeter, which is used to assess retinal sensitivity within, and adjacent to, retinal areas of specifi c interest. (Reproduced with kind permission of Nidek Technologies.)

Plate 12 (Fig. 7.12) Selection of colour vision tests: a, City colour vision test; b, Ishihara plates; c, Jumbo D15 (PV16) (buttons), which are of particular use when testing patients with a visual acuity of 6/20 or less.

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Plates 13 & 14 (Fig. 9.2) Television viewing at 2 m (Plate 13), resulting in a doubling of size compared with viewing at 4 m (Plate 14). In this case the change in accommodative demand (0.5D for 2-m viewing and 0.25D for 4-m viewing) is likely to be within the patient’s depth of focus (tolerance to blur), and hence a distance prescription is still appropriate.

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Plate 15 (Fig. 14.1) A range of EVES.

Plate 16 (Fig. 15.1) High contrast, large print, tactile cooking items.

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Plate 17 (Fig. 15.2) Other items for the kitchen.

Plate 18 (Fig. 15.3) Marked up cooker, cup with liquid level indicator, and high contrast kettle.

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Plate 19 (Fig. 15.5) Large print, high contrast and tactile games.

Plate 20 (Fig 15.7) Writing guide, typoscope, and raised and thick lined paper.

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Plate 21 (Fig. 15.8) Range of writing implements and the visibility of their ink against a white paper background.

Plate 22 (Fig. 15.9) Mobility and symbol canes.

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Plate 23 (Fig. 15.10) Electronic reader.

Plate 24 (Fig. 16.4) Guide dog and user.

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Plates 25 & 26 (Fig. 18.1) Place setting as seen by someone with normal vision (Plate 25) and how it may be seen by someone with visual impairment (Plate 26).

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Plates 27–32 (Fig. 18.2) Real world scenes and how they may be seen by someone with visual impairment: street scene (Plates 27 & 28);

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Plates 27–32 (Fig. 18.2) countryside view (Plates 29 & 30);

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Plates 27–32 (Fig. 18.2) diffi culties encountered in a supermarket environment (Plates 31 & 32).

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CHAPTER

Epidemiology has been defi ned as ‘the study of the distribution, determinants and control of diseases in human populations’.1 When applied to the world of ophthalmology and optometry, it concerns the identifi cation, management and prevention of eye disease, in different populations, so as to promote normal vision, to prevent blindness and visual impairment, and to preserve ocular health. Fundamental to the process of providing low vision care to visually impaired persons is an understanding of the ter-minology surrounding visual impairment. This chapter seeks to highlight a range of regularly quoted defi nitions and to review the causes of visual impairment from a global perspective.

1.1 Defi nitions of visual impairment

Many of the defi nitions used to describe visual impairment have evolved as organisations responsible for healthcare management

SECTION ONE

Ophthalmology for low visionSection Editor: Giuliana Silvestri

Epidemiology of low visionA. Jonathan Jackson

111

1

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Ophthalmology for low vision

2

and the delivery of services in the developed world have attempted to classify disability in such a way as to control, or alternatively enhance, access to services or benefi ts. The term ‘blind’, which depends on the context in which it is used, may be preceded by the words ‘educationally’, ‘legally’ or ‘functionally’, and is often used to indicate profound visual impairment requiring specialist services or fi nancial assistance. This term, which is highly emotive, has also been used in the title deeds of many voluntary sector service providers that depend on the generosity of the public at large, such as the Royal National Institute for the Blind (RNIB), Guide Dogs for the Blind Association (GDBA) and the Blind Centre for Northern Ireland (BCNI). Regrettably the term now carries with it the perception that ‘all sight is gone’ and that the individual thus affected is helpless and, to some extent, to be pitied. This in itself can cause embarrassment and diffi culty for those labelled with the term, as at some later date they may be identifi ed by peers and others in society, including shopkeepers, bus drivers and volunteer helpers, as having some form of usable vision. The per-ception thus taken is that they have falsely acquired the title.

Terminology used to describe less severe forms of visual impair-ment includes ‘partial sight’, ‘low vision’ and ‘subnormal vision’. A review of the literature illustrates how these terms have been used almost synonymously and that preference for one as opposed to another changes with time. In peer-reviewed ophthalmic litera-ture published in the UK, the terms ‘blind’ and ‘partial sight’ are usually linked with data on registration, whereas the terms ‘low vision’ and ‘subnormal vision’ have been used when referring to the provision of optometric services for the visually impaired. The term ‘visual impairment’ has been used to describe a broader spec-trum of sight loss. In recent years, in an attempt to de-stigmatise visual impairment, more general descriptive terms referring to ‘sight loss’ and ‘problems associated with vision’ have been advo-cated by some. Unfortunately many of these terms are not clearly defi ned and their introduction contributes to confusion in the epidemiological world, leading at times to greatly overestimated prevalence values for severe visual impairment.

1.1.1 World Health Organization defi nitions

Since its inception in the 1940s the World Health Organization (WHO) has shown an interest in the prevention of blindness. In 1973 the WHO highlighted that one of the major problems associ-

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1Epidemiology of low vision 11

3

ated with the collection of defi nitive data on visual disability was the non-standardisation of defi nitions.2 It is estimated that, on a worldwide scale, 65 different defi nitions of blindness and poor vision are in existence. By 1978, in an attempt to bring a degree of consistency to the classifi cation of visual disability and blindness, the WHO proposed a standard classifi cation that could be used on a worldwide basis.3 The proposals were subsequently included in the tenth revision of the International Statistical Classifi cation of Diseases and Related Health Problems (ICD-10).4 Regrettably the classifi cation has not been universally adopted, although refer-ences to it are now common (Table 1.1).

1.1.2 Blind and partially sighted registration defi nitions

In the UK the statutory defi nition of blindness, as defi ned in the 1920 Blind Persons Act5 and subsequently incorporated into the 1948 National Assistance Act6 states that a person is ‘so blind as to be unable to perform work for which eyesight is essential’. It is the

Table 1.1 WHO Defi nitions of Visual Impairment3,4

Category of visual Visual acuity with best possible correctiona

impairment Maximum less than Minimum equal to

or better than

Low vision

1 6/18 (20/60) [0.5] 6/60 (20/200) [1.0]

2 6/60 (20/200) [1.0] 3/60 (20/400) [1.3] CF at 3 m

3 3/60 (20/400) [1.3] 1/60 (20/1200) [1.8] CF at 3 m CF at 1 m

Blindness

4 1/60 (20/1200) [1.8] Light perception (PL) CF at 1 m

5 No perception of light (NPL)

9 Undetermined or unspecifi ed

a Values are Snellen metres, (Snellen feet) and [LogMAR]. CF, count fi ngers.

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4

responsibility of the consultant ophthalmologist to certify a visu-ally impaired person and, thus, to open the door for them to access community social services. With respect to registration, the fol-lowing points are of note:

1 The defi nition regarding blind registration is not whether the person is unable to pursue his or her ordinary occupation, but rather whether he or she is too blind to be able to perform any work for which eyesight is essential.

2 Although information concerning other contributory factors is requested on the blind registration form, advisory notes that accompany the form clearly state that in defi ning vision impairment these conditions should be disregarded, with only the visual problems being taken into account.

Clinical guidelines issued subsequent to the 1948 Act indicate that blind registration should be restricted to those whose visual acu-ities fall within one of three groupings (Table 1.2). If the extent of the visual fi eld is taken into account, patients with a visual fi eld radius no greater than 10° but greater than 5° around central fi xa-tion should be placed in category 2, and those with a fi eld no greater than 5° around central fi xation should be placed in category 3, even if the central acuity is not impaired. No indication is given, however, with regard to the methods used to quantify visual fi eld loss. Interestingly, those with homonymous or bitemporal hemi-anopia, who have retained a central acuity of 6/18 [LogMAR 0.5] or better, are to be excluded from blind registration. Guidance concerning the impact of recent, as opposed to long standing, visual impairment is considered by most to be ambiguous.

Table 1.2 Quantifi able Categories of Blindness, UK5,6

Group Description

1 Visual acuity of less than 3/60 [1.3] or less than 1/18 [1.25] if tested at a closer distance, in a patient with full visual fi elds

2 Visual acuities ranging from 3/60 [1.3] to less than 6/60 [1.0] with signifi cantly contracted visual fi elds

3 Visual acuity of 6/60 [1.0] or better with a gross visual fi eld constriction, particularly in the lower fi eld

[LogMAR equivalent acuities]

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5

Within the statutory context of the 1948 Act, no exact defi nition of less profound visual impairment is given, although subsequent guidelines defi ne the partially sighted as ‘those who are substan-tially and permanently handicapped by defective vision caused by congenital defect, illness or injury’. Guidelines concerning visual acuity requirements are generally considered to be more fl exible than those adopted for blind registration. Further clarifi cation is given to those who are responsible for the certifi cation of children, in that those with visual acuities of 6/24 [LogMAR 0.6] or better should be considered candidates for mainstream schooling. Chil-dren, ‘unless obviously blind’, should only be classifi ed as ‘par-tially sighted’, and at the age of 4 years and over the binocular vision should be considered as the determining criterion.

The clinical guidelines for partially sighted registration, released subsequent to the 1948 Act, are outlined in Table 1.3.

Until recently three different types of registration form have been used in the UK: BD8 in England and Wales, BP1 in Scotland and A655 in Northern Ireland. The BD8, the most recent version of which was introduced in 1990, was a four-part document that included information on visual status in part A, information rele-vant to ocular health in part B, a section on proposed registration status in part C, and treatment plans and education or employ-ment recommendations in part D. The BP1 and A655 were broadly similar in concept, although the layout of the forms was entirely different. All forms included ophthalmological data, designed to be held on an epidemiological database.

The year 2003 brought changes to the registration system in England. These changes were designed to:

• Assist with the early identifi cation of visual impairment for social care intervention

Table 1.3 Quantifi able Categories of Partial Sight, UK6

Group Description

1 Visual acuity of 3/60 [1.3] to 6/60 [1.0] with full fi elds

2 Visual acuity of up to 6/24 [0.6] with a moderate fi eld constriction, medial opacities or aphakia

3 Visual acuity of 6/18 [0.5] or better with a gross fi eld defect (i.e. hemianopia)

[LogMAR equivalent acuities]

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6

• Increase registration uptake• Improve the accuracy of data collection on the incidence and

type of eye disease resulting in visual impairment.

Three new forms were proposed: the CVI 2003, which will replace the conventional certifi cation/registration form; the LVI 2003, which is designed to initiate referrals from optometrists to social services; and the RVI 2003, which is designed for use by non-consultant hospital eye service staff. Interestingly all three forms contain sections on disability and the impact of visual impairment on daily living. Information targeted specifi cally at those who may have a driving licence has been highlighted, drivers having been warned of the consequences of driving when vision fails to meet the standard requirements (http://www.dh.gov.uk/PolicyAnd Guidance/HealthAndSocialCareTopics/fs/en). In Scotland the recommendations of a review on registration, carried out in 2001, are in the process of implementation.7 In Northern Ireland the Department of Health and Social Services introduced new certifi -cation and registration forms, based on the CVI, LVI and RVI mainland equivalents, to the province in the spring of 2005.

In the USA, state aid became available to the visually impaired in the 1930s, whereas the legal defi nition of blindness was intro-duced under the Social Security Act in 1935.8 Blindness is defi ned as a best corrected visual acuity in the better eye of less than or equal to 20/200 [LogMAR 1.0] or, if the visual acuity in that eye is better than 20/200 [LogMAR 1.0], a visual fi eld of less than or equal to 20° in the widest diameter. Having been classifi ed as legally blind, the visually impaired person becomes eligible to receive supplementary security income and social disability insur-ance. In Canada those classifi ed as legally blind are eligible to receive all of the services available through the Canadian National Institute for the Blind (CNIB).9 Similar statutory registration systems exist in many other developed countries.

Within a European context, research has indicated that of 47 states only 33 have a legal defi nition of blindness or visual impair-ment. Of these, only two sets of defi nitions were entirely consistent with WHO guidelines. Thirty-seven states utilised quantifi able data on visual acuity, whereas only 16 used defi nitions that included reference to visual fi eld size, to defi ne levels of visual impairment. Other states use functional defi nitions based on employment and social welfare law. In the Netherlands, for example, the blind are defi ned as ‘those who are obliged to read

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7

Braille or make use of the spoken word’, whereas in Norway the defi nition is applied to ‘those who have reduced vision to the extent that it is impossible or diffi cult to read normal writing and or orientate themselves with the help of sight’.10 Information on European defi nitions, although not always available in a consistent and comparable format, can be obtained from the European branch of the World Blind Union (http://www.worldblindunion.org).

Registration anomalies

The astute reader and experienced low vision practitioner will be acutely aware of the problems associated with defi nitions linked to registration. Visual fi eld specifi cations are of course dependent on the target size and brightness, whereas visual acuity measure-ments fl uctuate widely depending on testing conditions and, in particular, lighting conditions. The visually impaired individual, tested by a zealous clinician in a properly illuminated consult-ing room, may be unfairly classifi ed as being partially sighted, whereas, if tested by another more sympathetic practitioner in suboptimal conditions, may be registered as blind. It is also impor-tant to remember that visual acuity can vary from day to day with some conditions such as diabetic retinopathy and multiple sclero-sis. These factors become particularly important if registration is being embarked upon as a process through which access to bene-fi ts will be gained. The all or nothing concept linking registration to benefi t entitlement is a particular cause of concern.

These factors, together with others associated with psychologi-cal attitudes to registration, help to explain some of the epidemio-logical anomalies inherent in registration data, as highlighted in articles by Bunce et al,11 Evans & Wormald12 and Robinson et al.13 Bunce et al concluded that registration data are biased towards permanent non-treatable causes of central visual loss. Robinson et al highlighted the need to remove the ‘negative perceptions’ asso-ciated with registration held by professionals, and stressed the need to target the elderly and those with chronic sight-threatening eye disease.

1.1.3 Disorder, impairment, disability and handicap

For many years the terms impairment, disability and handicap have been used inappropriately. These terms are neither synony-mous nor interchangeable. They represent different aspects of the

Ch001-H1815.indd 7 9/15/2006 11:35:36 AM


8

problems that result from a disturbance of human functioning. The International Classifi cation of Impairment, Disability and Handicap (ICIDH-2/1980), introduced by the WHO in 1980, attempted to standardise the terminology in terms of the func-tional consequences of the disease process (Table 1.4).14

Table 1.5 indicates how the 1980 classifi cation applies to a number of ophthalmic conditions. An understanding of the concept helps to bridge the gap between the results obtained when recording quantifi able visual function data in the clinical environ-ment and the statements made to describe the impact that sight loss has on an individual patient. Two individuals with exactly the same degree of impairment may experience entirely different levels of disability and handicap. The taxi driver with a best cor-rected visual acuity of 6/18 [LogMAR 0.5] resulting from macular oedema of recent onset will fi nd the withdrawal of a driving licence devastating from both an economic and social perspective, whereas an adult with congenital nystagmus, who never drove in the fi rst place, may cope with impaired visual function without great diffi culty.

In 2000, the classifi cation was upgraded to ICIDH-2/2000 and renamed the International Classifi cation of Functioning, Disabil-ity and Health.15 The new classifi cation provides a multiperspec-tive approach to the classifi cation of functioning and disability as an interactive and evolutionary process. It allows both scientifi c

Table 1.4 International Classifi cation of Impairment, Disability and Handicap Introduced by the WHO in 1980 (ICIDH-2)14

Disorder Usually used to describe the impact of the disease or injury on the anatomical structure of visual function within the organ or, in the case of vision, a component of the visual pathway

Impairment The consequence, in terms of measurable loss or departure from functional capacity, to the bodily organ, affected by disorder or disease, of an anatomical or physiological function

Disability The consequence to the patient in terms of the effect of the impairment on the patient’s abilities

Handicap The consequence of the disability in terms of how it affects the patient’s ability to interact with society

Ch001-H1815.indd 8 9/15/2006 11:35:36 AM


9

Ta

ble

1.5

Cla

ssifi

cati

on o

f Lo

ss o

r Im

pair

men

t –

Dis

orde

r an

d Im

pair

men

t R

elat

e to

the

Org

an w

here

as D

isab

ility

and

H

andi

cap

Rel

ate

to t

he P

erso

n

T

he o

rgan

T

he p

ers

on

D

iso

rde

r Im

pair

me

nt

Dis

ab

ilit

y

Ha

nd

ica

p

Des

crip

tion

D

isea

se o

r in

jury

R

educ

ed f

unct

iona

l R

educ

ed s

kills

or

abili

ties

Li

mit

atio

ns o

n so

cial

perf

orm

ance

part

icip

atio

n

Exam

ple

1 A

ge-r

elat

ed m

acul

ar

Red

uced

VA

and

CS

Rea

ding

spe

ed a

nd fl

uen

cy

Diffi

cul

ty in

ass

essi

ng

dege

nera

tion

redu

ced

wri

tten

mat

eria

l and

corr

espo

nden

ce

Exam

ple

2 R

etin

itis

pig

men

tosa

C

ontr

acte

d V

F, r

educ

ed

Wal

king

spe

ed r

educ

ed,

Lim

itat

ions

to

unac

com

pani

ed

C

S an

d im

pair

ed n

ight

M

obili

ty p

robl

ems

trav

el a

nd r

esul

ting

soc

ial

visi

on

is

olat

ion

Exam

ple

3 C

onge

nita

l cat

arac

ts

Red

uced

VA

and

CS,

N

ear

visi

on t

asks

incl

udin

g D

iffi c

ulti

es w

ith

educ

atio

nal

(a

phak

ia)

glar

e di

sabi

lity

and

read

ing

mor

e di

ffi cu

lt th

an

deve

lopm

ent

redu

ced

near

acu

ity

dist

ance

tas

ks

Exam

ple

4 O

culo

cuta

neou

s R

educ

ed V

A a

nd C

S,

Ori

enta

tion

diffi

cul

t in

R

estr

icti

ons

to

albi

nism

an

d ph

otop

hobi

a br

ight

ligh

t. P

robl

ems

wit

h ce

rtai

n tr

avel

tas

ks

dist

ance

vis

ion

CS,

con

tras

t se

nsit

ivit

y; V

A, v

isua

l acu

ity;

VF,

vis

ual fi

eld

.

Ch001-H1815.indd 9 9/15/2006 11:35:36 AM


10

investigations and clinical/rehabilitation providers to map differ-ent aspects of the process. Table 1.6 illustrates how disruption of bodily function has an impact on a person’s abilities and how these can have difference consequences, depending on the impact of both environmental and personal factors on the situation. The concept is more complex to grasp than that outlined in the original ICIDH and, as such, the author feels, within the world of visual impairment, that it does not supersede the original concept.

1.1.4 Low vision

Those approaching the problem of visual impairment from an optical or optometric background advocate the term ‘low vision’, which to a large extent has evolved from the term ‘subnormal vision’. This term is almost synonymous with visual impairment, with the added provision that the residual vision is usable. Those persons who are totally blind, having a visual acuity of no percep-tion of light in both eyes, make up less than 6% of the visually impaired population, and those with a visual acuity of perception of light only, a further 5%. Some 11% of visually impaired persons are therefore not included in the category of low vision patient. Low vision could thus be defi ned as ‘vision that, when corrected by optimal refractive correction, is not adequate for the patient’s needs’. Low vision is thus a functional defi nition that can be applied easily to any patient with a disease or disorder affecting the visual system. Some authorities advocate the term ‘residual vision’, empha-sising that attention needs to be paid to that which has been retained rather than that which has been lost. In dealing with rehabilitation issues, this is particularly important to the patient.

1.2 Epidemiology

Although epidemiology began with the study of infectious disease outbreaks such as cholera, it has expanded in such a way that the methodology can be applied to the study of any disease process affecting human populations.1,16

1.2.1 Epidemiological methodologies

Strategies used in epidemiological research can essentially be grouped into two main categories: those that involve

Ch001-H1815.indd 10 9/15/2006 11:35:36 AM


11

Ta

ble

1.6

IC

IDH

-2 O

verv

iew

of

the

Func

tion

al C

lass

ifi ca

tion

of

Dis

abili

ty a

nd H

ealt

h15

F

un

cti

on

ing a

nd

dis

ab

ilit

y

Co

nte

xtu

al

facto

rs

F

un

cti

on

an

d

Acti

vit

ies

an

d

En

vir

on

me

nta

l P

ers

on

al

st

ructu

re

parti

cip

ati

on

Dom

ains

B

odily

fun

ctio

ns

Life

are

as (

i.e. t

asks

and

Ex

tern

al in

fl uen

ces

Inte

rnal

infl u

ence

s

Bod

y pa

rts

acti

ons)

Con

stru

cts

Phys

iolo

gica

l cha

nge

Cap

acit

y an

d pe

rfor

man

ce

Hin

dran

ces

of f

eatu

res

Impa

ct o

f at

trib

utes

A

nato

mic

al c

hang

e

in t

he p

hysi

cal o

r so

cial

on

per

son

w

orld

Posi

tive

asp

ects

Fu

ncti

onal

and

A

ctiv

ity

part

icip

atio

n Fa

cilit

ator

s N

ot a

pplic

able

st

ruct

ural

inte

grit

y

Func

tion

ing

Neg

ativ

e as

pect

s Im

pair

men

t A

ctiv

ity

limit

atio

n B

arri

ers

and

hind

ranc

es

Not

app

licab

le

Dis

abili

ty

Part

icip

atio

n re

stri

ctio

n

D

isab

ility

Ch001-H1815.indd 11 9/15/2006 11:35:36 AM


12

interventional experimental design (randomised controlled trials or community interventions) and those that can be described as utilising observational design (cross-sectional, case-controlled and longitudinal studies).

In the case of the randomised controlled trial, individuals invited to take part in the study, using predetermined inclusion or exclusion criteria, are allocated randomly to a treatment type or intervention, whereas others are allocated to a control or placebo-type group. Outcomes are assessed by individuals who are, where possible, unaware of which arm of the study patients have been allocated to. For studies involving recruitment of a small sample, allocations may have to be stratifi ed to help ensure similarity between the groups. The nature of randomised con-trolled trials necessitates that the treatment under evaluation be withheld from one group. Although this can be diffi cult for patients to accept, it is essential for proper evaluation of the therapy. It is important to explain the process carefully to the patient and to enable them to understand that the treatment is not yet proven and may have signifi cant side-effects.

Observational studies differ in that populations are examined according to whether they have, or have not, been exposed to factors that may have an impact on health and disease. A popula-tion exposed to high levels of ultraviolet radiation over prolonged periods of time, in whom cataract is prevalent, may be compared, for example, with a group of individuals who have had no such exposure. The major problem with this type of study is the need to compensate for confounding factors such as environmental exposures, genetic predisposition, or a combination of the two. An understanding of the terms ‘prevalence’ and ‘incidence’ is crucial to the appreciation of epidemiological studies.

Prevalence =

Defi nition of Prevalence and Incidence

Incidence =

No. of cases or events

Total population at risk

No. of new cases over a given time interval

Total population at risk at the beginning of the specifi ed time

Ch001-H1815.indd 12 9/15/2006 11:35:36 AM


13

A more sophisticated way of expressing incidence is, however, to use the incidence rate, which considers the number of new cases occurring over the course of a follow-up study in relation to the total number of persons at risk during the same period. Practitio-ners involved in the provision of low vision services may be more interested in the prevalence of age-related macular degeneration (AMD) in the community, whereas the contact lens practitioner may be interested in the incidence of soft contact lens-related microbial keratitis. AMD is a chronic, essentially untreatable, con-dition that requires long-term rehabilitative intervention, whereas contact lens-related microbial keratitis is an acute condition that, if treated effectively, usually resolves rapidly, leaving the patient visually unaffected.

Other methods of expressing epidemiological data, relevant to visual impairment, include the specifi cation of the regional burden of blindness (RBB) and the age blindness burden (ABB).

RBB =

Defi nition of Regional Burden of Blindness and the Age Blindness Burden

ABB =

Percentage of the world’s blind population living within a region of interest

Percentage of the world’s total population living within the designated region of interest

Percentage of the world’s blind population in a specifi ed age group

Percentage of the world’s total population that falls within that age group

The RBB equation essentially attempts to determine whether there is an equitable distribution of blindness within an area in com-parison to other regions. If, for example, there are 510 million people living in sub-Saharan Africa, 7.1 million of whom are blind, the prevalence of blindness in the region is 1.4%. This compares to a global prevalence fi gure of 0.7%. The RBB in sub-Saharan Africa, which has an overall population of 510 million and repre-sents 9.7% of the world’s population of 5.26 billion, is thus 1.9. A value greater than 1 indicates a need to prioritise the treatment and prevention of blindness in the specifi ed region.

Application of the ABB equation to global fi gures of blindness illustrates the impact of degenerative eye disease on an ageing population. On a global basis, ABB rises from 0.12 in children

Ch001-H1815.indd 13 9/15/2006 11:35:36 AM


14

under the age of 15 years to 2.68 in adults between the ages of 45 and 59 years. Differences in the elderly population become more marked when comparing ABB values for the developed world with those for the developing world. Another unit of measure-ment, worthy of note, is the disability-adjusted life-year (DALY). This measurement combines the infl uence of premature loss of life, which is more prevalent in the developing world, with the loss of healthy life-years from disability.17

1.2.2 Global epidemiology

Although analysis of registration data from developed countries with adequate social care facilities provides a basis for compari-son, an entirely different approach has to be taken when looking at the incidence and prevalence of visual impairment in the devel-oping world. In these cases prevalence has to be established from representative community-based studies, the results of which need to be extrapolated to the population as a whole. Thylefors et al18 divided world data into eight economic regions and examined the prevalence accordingly. In established market economies, including western Europe, the USA, Australia, New Zealand and Japan, the prevalence of blindness is estimated as 0.3%. In Latin America, China and the Middle East it rises to 0.5–0.7%, whereas in Asia and India the proportion rises to almost 1.0%. Most strik-ingly the prevalence in sub-Saharan Africa is approximately 1.4%. The overall global estimate of blindness is 45 million, with a further 135 million individuals classifi ed as having low vision (Table 1.7, Fig. 1.1).19

Another striking factor is the relative distribution of blindness according to age across the world. In the developed world blind-ness is most likely to be associated with essentially untreatable degenerative processes associated with ageing, whereas in the developing world there is a much higher prevalence of prevent-able childhood blindness. In China, sub-Saharan Africa and the Middle East an estimated 16 million people are blind as a result of cataracts, whereas 5.9 million are blind from trachoma. A further 0.3 million residents in Central and West Africa are blind from onchocerciasis. The latter two conditions have, to all intents and purposes, been eliminated from countries with established market economies. Blindness resulting from cataract represents less than 4% of the overall burden of blindness in the developed world, whereas lack of access to cataract surgery in the

Ch001-H1815.indd 14 9/15/2006 11:35:37 AM


15

developing world ensures that cataract remains a major cause of blindness.

Foster & Gilbert20 estimated that, of the 1.5 million blind chil-dren worldwide, 1.3 million reside in Asia and Africa, and that 75% of this blindness could have been prevented or is curable. The prevalence rate for childhood blindness in Europe and North America (0.03%) contrasts markedly with that in Africa (0.11%). Similarly, causes differ according to region. Genetic causes account for the majority of childhood visual impairment in the devel-oped world, whereas in the developing world infection, in-cluding measles and rubella, causes intrauterine and infant visual

Table 1.7 The Global Distribution of Blindness1,19

Estimated Regional Regional Major

no. of blind prevalence blindness causes by

people of blindness burden region

(millions) (%)

Established 2.4 0.3 0.41 AMD 50%market Glaucoma 8%economies

Former 1.1 0.3 0.41 AMD 84%socialist Glaucoma 7%block Cataract 8.3%

Latin and 2.3 0.5 0.72 Cataract 57%Central Glaucoma 8%America

China 6.7 0.6 0.82 Cataract 32% Glaucoma 8%

Middle East 3.6 0.7 0.74 Cataract 45% Trachoma 25%

Asia 5.8 0.8 1.18 Cataract 39% Trachoma 24%

India 8.9 1.0 1.46 Cataract 51% Glaucoma 12%

Sub-Saharan 7.1 1.4 1.93 Cataract 43%Africa Trachoma 19%

Overall 37.9 0.7 1.0

Ch001-H1815.indd 15 9/15/2006 11:35:37 AM


16

impairment. Distressingly, between 60% and 80% of children who become blind die within 2 years of having become blind.21

1.2.3 Epidemiology in the UK

Epidemiological data on visual impairment in the UK is generally taken from one of three sources. The most widely quoted fi gures, which most authorities agree underestimate the true extent of the problem, are those obtained from regional blind and partially sighted databases. More detailed data, which tend to be collected by locality and relate to population subgroups (the elderly, children, or those with specifi c disease entities), appear in peer-reviewed medical and scientifi c publications. In addition, voluntary sector organisations and those dealing with the rehabilitative requirements of the visually impaired often use information extracted from government census returns and population surveys on self-perceived levels of visual impairment.

Figure 1.1 Estimated prevalence of blindness according to World Bank economic regions. EME, established market economies; FSE, former socialist market economies; LAC, Latin America and Caribbean countries; CHI, China; MEC, Middle Eastern crescent; ACI, Asian countries and islands; IND, India; SSA, sub-Saharan Africa. (Adapted from Johnston & Foster 1998.1)

EME 0.3%FSE 0.3%LAC 0.5%CHI 0.6%

MEC 0.7%ACI 0.8%IND 1.0%SSA 1.4%

Ch001-H1815.indd 16 9/15/2006 11:35:37 AM


17

Registration data

Within the UK, registration data have been scrutinised since the 1950s when Arnold Sorsby published the fi rst of his comprehen-sive reviews on the subject.22 Data pertaining to the past 15 years have been analysed extensively by Evans and co-workers.23,24 Current data from all four UK regions can be accessed via depart-mental websites:

• England – http://www.dh.gov.uk/PublicationsAndStatistics/ Statistics/StatisticalWorkAreas/StatisticalSocialCare/fs/en

• Wales – http://www.dataunitwales.gov.uk/eng/Data.asp?cat=252

• Scotland – http://www.scotland.gov.uk/stats/bulletins/00292-00.asp

• Northern Ireland – http://www.dhsspsni.gov.uk/comstats_04.pdf

Recent fi gures indicate that there are approximately 377 000 indi-viduals registered as blind or partially sighted in the UK (Table 1.8). The ratio of those registered as partially sighted to those reg-istered as blind has, over a 20-year period, changed from approxi-mately 1 : 2.5 to almost 1 : 1 in England and Wales, whereas in Scotland partially sighted registration still appears to be unrepre-sentative of the true prevalence of moderate visual impairment (Fig. 1.2).

The levelling off in blind registration and the progressive increase in partially sighted registration is in keeping with

Table 1.8 Regional UK Blind and Partially Sighted Registration Data (2004)

Region Registration status (n) Estimated

prevalence (%)

Blind PS Total

Blind PS Total

England 156 675 155 230 311 905 0.32 0.31 0.63

Wales 9 643 10 565 20 208 0.33 0.36 0.69

Scotland 23 557 14 443 38 000 0.46 0.28 0.74

Northern 2 273 3 122 5 395 0.14 0.18 0.32Ireland

PS, partially sighted.

Ch001-H1815.indd 17 9/15/2006 11:35:37 AM


18

Figure 1.2 Changing trends in blind and partially sighted registration in the UK, recorded over a 20-year period.

350000300000250000200000150000100000

500000

25000

20000

15000

10000

5000

40000

30000

20000

10000

0

01000200030004000500060007000

0

1984

1982

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

1984

1982

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

England

Wales

Year

Year

1984

1982

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

Year

1984

1982

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

Year

Scotland

N. Ireland

Partially sighted Blind Total registered

Num

ber o

f ind

ivid

uals

Num

ber o

f ind

ivid

uals

Num

ber o

f ind

ivid

uals

Num

ber o

f ind

ivid

uals

Ch001-H1815.indd 18 9/15/2006 11:35:37 AM


19

changing population demographics (ageing) and an associated increase in degenerative ophthalmic pathology, which results in moderately severe central visual loss (AMD).

Detailed analysis of registration data is, however, undertaken only sporadically. Evans & Wormald,25 in a review of English blind registration data collected since the 1950s, found that, once cor-rected for changing age profi les in the population, only registra-tion rates attributable to AMD showed an increasing trend (from 6% in 1933–1943 to 49% in 1990–1991). Registration rates resulting from glaucoma and optic atrophy showed a small but signifi cant decline, whereas blind registrations resulting from cataract decreased by a factor of 12 over the same time interval. Analysis of the causes of blind, as opposed to partially sighted, registration in England and Wales, undertaken in 1990 and 1991, indicated that only for cataract did the trends for blindness and partial sight differ signifi cantly (Fig. 1.3):23,24

• Blind registrations – AMD 48.5%, glaucoma 11.7%, diabetic retinopathy 3.4%, optic atrophy 3.4%, cataract 3.3%

• Partially sighted registrations: AMD 46.5%, glaucoma 9.6%, cataract 7.0%, diabetic retinopathy 3.0%, optic atrophy 2.3%.

New registration data for Northern Ireland, collected over a 15-year period (1984–1996), illustrate similar trends.26

Figure 1.3 Causes of blind and partially sighted registration by primary ophthalmic disease. (Adapted from Evans 1995.23)

No information on main cause GlaucomaMacular and postpolar degenerationOther conditions

CataractOptic atrophyDiabetic retinopathy

20% 23.1%9.7% 8.5%

7%2.3%

3%

9.6%

3.3%3.4%

3.4%

11.7%

48.5% 46.5%

Blind Partial sight

Ch001-H1815.indd 19 9/15/2006 11:35:37 AM


20

Analysis of 1980–1981 and 1990–1991 data published by Evans et al23–25 highlights the extent to which both blindness and partial sight disproportionately affect the elderly:

• Blind registrations – age 0–15 years, 3 per 100 000 population; 16–64 years, 5 per 100 000; 75–84 years, 200 per 100 000; 85 years and over, 530 per 100 000

• Partially sighted registrations – age 0–15 years, 4 per 100 000 population; 16–64 years, 7 per 100 000; 65–74 years, 66 per 100 000; 75–84 years, 231 per 100 000; 85 years and over, 416 per 100 000.

This burden of age-related visual impairment is likely to increase as the population ages.

Population-based data

Most data relating to population-based studies are specifi c to the age-related degenerative conditions that affect the elderly. The reason for this is that it is disproportionately expensive to collect prevalence data, using screening methodologies, for conditions that occur relatively infrequently. Important UK studies include those by Cullinan27 in 1978, Gibson et al28 in 1986, Lavery et al29 in 1988, Wormald et al30 in 1992, Reidy et al31 in 1998, Van der Pols et al32 in 2000 and Evans et al33 in 2002.

Lavery et al,29 in a general practice-based survey of 529 indi-viduals aged 75 years and older, living in Melton Mowbray, found that 18% of men and 30% of women had a visual acuity of 6/18 [LogMAR 0.5] or worse. Only 3.8% of this population group had a best corrected acuity of less than 6/36 [LogMAR 0.8]. Interest-ingly, 95% could achieve N10 or better with an appropriate near correction. Wormald et al,30 examining 207 individuals aged 65 years and older, recruited from general practice lists in inner London, found the prevalence of blindness (WHO) to be 1% and the prevalence of visual impairment (visual acuity less than 6/15 [LogMAR 0.4]) to be 7.7%. Van der Pols et al,32 as part of the National Diet and Nutrition Survey of those aged 65 years or more living in either private homes or nursing homes in the UK, found that 9.3% had a habitual or pinhole visual acuity of less than 6/18 [LogMAR 0.5]. Interestingly, the prevalence of visual impairment was 3.5 times greater amongst those living in nursing homes.32 This fi nding confi rms what is known about the increased preva-lence of visual impairment amongst those with other forms of

Ch001-H1815.indd 20 9/15/2006 11:35:38 AM


21

disability.34 In the largest and most recent study, conducted on 14 600 subjects aged 75 years and over, from 53 general practice lists across the UK, Evans et al33 found that the prevalence of low vision (visual acuity less than 6/18 [LogMAR 0.5] to 3/60 [LogMAR 1.3]) was 10.3% and blindness (visual acuity less than 3/60 [LogMAR 1.3]) 2.1%. Acuity was measured using Glasgow Acuity Cards and recorded with both the habitual correction and, when indicated, a pinhole.33

A review of Gibson’s Melton Mowbray data indicated the extent of sight-limiting pathology in the elderly (cataract 46%, AMD 41%, primary open angle glaucoma 6.6%).28 Wormald et al30 further highlighted the fact that almost 75% of visual impairment in the elderly was potentially treatable through the provision of an appropriate refractive correction or cataract surgery. In a parallel study, Das et al35 provided evidence of a disproportionate degree of potentially treatable visual impairment in ethnic communities in the UK. Recent results from Evans et al,36 which complement previous registration reviews, indicate that of 1742 visually impaired elderly persons recruited from 49 general practices 32.0% had AMD, 20.4% cataract, 6.4% glaucoma and 2.1% diabetic eye disease. Most strikingly, 31.6% of this population subgroup were found to be visually impaired as a result of uncorrected refractive errors.36 Other regional and local studies from which UK data are available include those from Bristol,37 Bradford,38 Nottingham,39 Avon40 and Leicestershire.41

In addition to studies carried out in the elderly, a number of studies have examined the prevalence of visual impairment in children. Few studies have involved the screening of large popula-tion groups, although Stewart-Brown & Haslum42 investigated 15 000 children born between 5 and 11 April 1970, and found the prevalence of blindness to be 3–4 per 100 000 and that of partial sight to be 5–9 per 100 000. Research by Rahi & Cable,43 using alternative case-fi nding methodology, found higher prevalence rates, with a cumulative incidence of visual impairment in young children of 5.9 per 100 000 by the age of 16 years. Most importantly, 77% of these children were noted to have additional non-ophthalmic disabilities and disorders. Local studies from Oxford-shire,44 Liverpool45 and Belfast46 have confi rmed these fi ndings.

Government survey data

An alternative approach to collecting data from registration databases or from population-based studies involves the use of

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22

large-scale household surveys. The most well known of these, within the UK, is the Offi ce of Population Censuses and Sur-veys (OPCS) Disability Survey.47 In the survey, which was sent to 100 000 private households, questions on visual disability asked about ‘diffi culty reading newspaper print and recognising a friend from across the road’. Questions were always appended with the phrase ‘even if glasses or contact lenses are worn’. Of the 20 415 individuals who responded ‘yes’ to one of the disability questions, 2534 were noted to have a self-reported visual dis-ability. Results recorded from communal institutions, including nursing homes, were subsequently included in the analysis. Estimated age-specifi c prevalence rates for visual impairment in the UK were calculated as 0.8% for those aged 16–59 years, 5.6% for those aged 60–74 years and 26.2% for those over 75 years. Using these data, the estimated number of individuals in the UK who are visually impaired approaches 1.5 million. Analysis of similar Family Resource Survey data by Grundy et al48 indicates that this fi gure could be as high as 1.9 million. This represents almost 25% of all disabled adults. A supplementary survey on those identifi ed from previous government-based surveys carried out by the RNIB and using self-reported questionnaires found the prevalence of signifi cant visual impairment (diffi culty reading newsprint) to be 2.8% of all adults and 14.4% of those over 75 years of age.49

1.3 Summary

This chapter seeks to highlight the importance of epidemiology in the detection, treatment and long-term management of eye disease resulting in visual impairment. Fundamental to the process is the need to use internationally agreed defi nitions of disease, impair-ment, disability and handicap as outlined by the WHO, and of working towards agreed defi nitions of visual impairment, blindness and low vision. The situation concerning data collection in the UK has been reviewed and important issues concerning blind and partially sighted registration highlighted. Readers have, in addition, been shown how causes of visual impairment can vary greatly depending on location and sampling methodology. Differ-ences between the UK and other global geographical locations have been highlighted.

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23

References

1. Johnston GJ, Foster A. Prevalence, incidence and distribution of visual impairment. In: Johnston GJ, Minassion DC, Weale R, eds. The epidemiology of eye disease. London: Chapman & Hall; 1998:7–30.

2. World Health Organisation. The prevention of blindness. Report of a WHO study group. WHO Technical Report Services 518. Geneva: WHO; 1973.

3. World Health Organisation. Guidelines for programmes for the prevention of blindness. Geneva: WHO; 1979.

4. World Health Organisation. International statistical classifi cation of diseases and related health problems (ICD-10). Geneva: WHO; 1992.

5. The Blind Person’s Act 1920. London: HMSO. 6. National Assistance Act 1948. London: HMSO. 7. Report of the Certifi cation and Registration Working Group. Social

work services for people with a sensory impairment. Edinburgh: Scottish Executive; 2001.

8. Goldstein H. The demography of blindness throughout the world. New York: American Foundation for the Blind; 1980.

9. Leat SJ, Legge GE, Bullimore MA. What is low vision? A re-evaluation of defi nition. Optometry and Vision Science 1999; 76:198–211.

10. Jackson AJ, Gallagher B, Hart PM. European blindness: a review of national defi nitions and currently available epidemiological data. Ophthalmic Research 2000; 32(Suppl 2):117.

11. Bunce C, Evans J, Fraser S, Wormald R. BD8 certifi cation of visually impaired people. British Journal of Ophthalmolgy 1998; 82:72–76.

12. Evans JR, Wormald RPL. Epidemiological function of BD8 certifi cation. Eye 1993; 7:172–179.

13. Robinson R, Deutsch J, Jones HS et al. Unrecognised and unregistered visual impairment. British Journal of Ophthalmology 1994; 78:736–740.

14. World Health Organisation. ICIDH-2. International classifi cation of impairment, disability and handicap. Geneva: WHO; 1980.

15. World Health Organisation. ICIDH-2. International classifi cation of functioning, disability and health. Geneva: WHO; 2000.

16. Minassian OC. Epidemiological research methods. In: Johnston GJ, Minassion DC, Weale R, eds. The epidemiology of eye disease. London: Chapman & Hall; 1998:33–61.

17. Bos E, Vu MT, Levin A, Bulatao RA. World population projection 1992–1993. Estimates and projections with related demography statistics. Baltimore: Johns Hopkins University Press; 1992.

18. Thylefors B, Negrel AD, Pararajasegaram R, Dadzie KY. Global data on blindness. Bulletin of the World Health Organisation 1995; 73:115–121.

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19. World Health Organization. Global initiative for the elimination of avoidable blindness. WHO/PBL 97:61, Rev 2. Geneva: WHO; 2000.

20. Foster A, Gilbert C. Epidemiology of childhood blindness. Eye 1992; 6:173–175.

21. Cohen N, Rahman H, Sprague J, Jalil MA, Leemhuis de Regt E, Mitra M. Prevalence and determinants of nutritional blindness in Bangladeshi children. World Health Statistics Quarterly 1985; 38:317–329.

22. Sorsby A. The causes of blindness in England and Wales. Medical Research Council Memorandum No. 24. London: HMSO; 1950.

23. Evans JR. Causes of blindness and partial sight in England and Wales 1990–1991. Studies on Medical and Population Subjects No. 57. London: HMSO; 1995.

24. Evans JR, Rooney C, Dattani N, Ashwood F, Wormald RPL. Causes of blindness and partial sight in England and Wales. Health Trends 1996; 28:5–12.

25. Evans JR, Wormald R. Is the incidence of registerable age-related macular degeneration increasing? British Journal of Ophthalmology 1996; 80:9–14.

26. Canavan YM, Jackson AJ, Stewart A. Visual impairment in Northern Ireland. Ulster Medical Journal 1997; 66:92–95.

27. Cullinan TR. Epidemiology of visual disability. Transactions of the Ophthalmological Society of the UK 1978; 98:267–269.

28. Gibson JM, Lavery JR, Rosenthal AR. Blindness and partial sight in an elderly population. British Journal of Ophthalmology 1986; 70:700–705.

29. Lavery JR, Gibson JM, Shaw DE, Rosenthal AR. Vision and visual acuity in an elderly population. Ophthalmic and Physiological Optics 1988; 8:390–393.

30. Wormald RPL, Wright LA, Courtney P, Beaumont B, Haines AP. Visual problems in the elderly population and implications for services. British Medical Journal 1992; 304:1226–1229.

31. Reidy A, Minassian DC, Vafi dis G et al. Prevalence of serious eye disease and visual impairment in a North London population: population based, cross-sectional study. British Medical Journal 1998; 316:1643–1646.

32. Van der Pols JC, Bates C, McGraw PV, Thompson JR, Reacher M, Prentice A, Finch S. Visual acuity measurements in a national sample of British elderly people. British Journal of Ophthalmology 2000; 84:165–170.

33. Evans J, Fletcher AE, Wormald R et al. Prevalence of visual impairment in peopled aged 75 years and above in Britain: results from the MRC trial of assessment and management of older people

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in the community. British Journal of Ophthalmology 2002; 86:795–800.

34. Warburg M. Visual impairment in adult people with intellectual disability: literature review. Journal of Intellectual Disability Research 2001; 45:424–438.

35. Das BN, Thompson JR, Patel R, Rosenthal AR. The prevalence of eye disease in Leicester – a comparison of adults of Asian and European descent. Journal of the Royal Society of Medicine 1994; 87:219–222.

36. Evans JE, Fletcher AE, Wormald RPL. Causes of visual impairment in people aged 75 years and above in Britain: an add on to the MRC trial of assessment and management of older people in the community. British Journal of Ophthalmology 2004; 88:365–370.

37. Clark JB, Grey RHB, Lim KKT, Burns-Cox CJ. Low of vision before ophthalmic referral in blind and partially sighted diabetics in Bristol. British Journal of Ophthalmology 1994; 78:741–744.

38. Yap M, Weatherill J. Causes of blindness and partial sight in the Bradford metropolitan district from 1980–1989. Ophthalmic and Physiological Optics 1989; 9:289–292.

39. Aclimandos WA, Galloway N. Blindness in the city of Nottingham (1980–1985). Eye 1988; 2:431–434.

40. Grey RHB, Burns-Cox CJ, Hughes A. Blind and partial sight registration in Avon. British Journal of Ophthalmology 1989; 73:88–94.

41. Thompson JR, Rosenthal AR. Recent trends in the registration of blindness and partial sight in Leicestershire. British Journal of Ophthalmology 1989; 73:95–99.

42. Stewart-Brown SL, Haslum MN. Partial sight and blindness in children of the 1970 birth cohort at 10 years of age. Journal of Epidemiology and Community Health 1988; 42:17–23.

43. Rahi JS, Cable N, British Childhood Visual Impairment Study Group. Severe visual impairment and blindness in children in the UK. Lancet 2003; 362:1359–1365.

44. Croft BJ, King R, Johnson A. The contribution of low birth weight to severe vision loss in a geographically defi ned population. British Journal of Ophthalmology 1998; 82:9–13.

45. Rogers M. Vision impairment in Liverpool: prevalence and morbidity. Archives of Disease in Childhood 1996; 74:299–303.

46. Flanagan NM, Jackson AJ, Hill AE. Visual impairment in children: insight from a community based survey. Child Health Care and Development 2003; 29:493–499.

47. Martin J, Meltzer H, Elliot D. The prevalence of disability among adults. OPCS surveys of disability in Great Britain,

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Report 1. London: Offi ce of Population Censuses and Surveys; 1988.

48. Grundy E, Ahlburg D, Ali M, Breeze E, Sloggett A. Disability in Great Britain: results from the 1996/1997 disability survey. Technical Report 94. London: Department of Social Security; 1999.

49. Royal National Institute for the Blind. Survey of the needs and lifestyles of visually impaired adults. Technical Report (1998/1999). London: Offi ce of National Statistics; 2000.

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Visual loss in childhood and the early teens is predominantly congenital or hereditary in nature.1 In this chapter the various conditions causing visual impairment in this age group are dis-cussed, with particular emphasis on the diagnostic features that are helpful in making the correct diagnosis. The three most common clinical scenarios presenting to the ophthalmologist are discussed in detail:

• The neonate or young baby who appears to be visually impaired

• The visually impaired baby with no obvious ophthalmic abnormality

• The child with visual diffi culty.

Recent advances in the understanding of the molecular genetics of many of these conditions have been truly exciting, and a brief review of the recent molecular discoveries is given where relevant.

2.1 Visual development

The refractive state of the normal neonate is 2–3 dioptres of hyper-metropia, accompanied by a high prevalence of astigmatism. At birth the globe measures 16.5 mm in diameter and over the fi rst year the diameter increases rapidly to reach an almost adult

27

CHAPTER

Visual impairment in the youngGiuliana Silvestri

222

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28

diameter of 24.5 mm.2 The spherical equivalent refractive error of full-term newborn infants is normally distributed about a mean of +2 dioptres with a standard deviation of 2 dioptres.3 The retina is well developed at term; however, the foveal region is immature, not reaching adult maturity until 4 months of age. The neural pathways are also immature at term, with cells in the lateral genic-ulate ganglion reaching adult size at age 2 years and the optic nerve becoming fully myelinated at 7 months. Coupled with increasing maturation of the visual system, the hypermetropic state reduces steadily and visual acuity improves. By the age of 20–30 months the visual acuity is estimated to be 6/6 [LogMAR 0.0]. In young children with a refractive error, the standard devia-tion of the error is greater the earlier the onset of the visual impair-ment; for example, the refractive error in tyrosinase-negative albinism would be much greater than that in Stargardt’s disease where near-normal variability is expected.

Practical advice

A baby who is emmetropic or myopic at birth is likely to become progressively more myopic during childhood and adolescence.

Practical advice

Eighty-three per cent of neonates will follow a face but not a white light. A smile in response to a silent smile should be present at 6 weeks of age and indicates good central vision.

2.2 Assessment of visual function

Assessment of the visual acuity of a neonate or a small baby requires patience, attention to detail and a modifi cation of the techniques used for adults. The examiner should be prepared to spend a substantial amount of time on the examination. At birth the full-term neonate can see colours and faces at arm’s length, and fi xation should be present. In the term infant, fi xation is the most reliable clinical test of visual function. The type of fi xation target used, however, is of paramount importance.

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2Visual impairment in the young 22

29

Visually directed reaching, although possible at 3–4 months, is usually not a useful clinical test until approximately 6 months of age. Other important signs in a baby who is suspected of being visually impaired include the presence of abnormal ocular move-ments, abnormal pupillary reactions (although often diffi cult to illicit in the neonate), the presence of eye rubbing or poking, lack of facial mobility or expression, and the absence of optokinetic nystagmus.

Practical advice

Abnormal eye movements and visual inattention are the most common signs of poor vision. The more uncoordinated the movements, the more impaired the visual acuity.

The parents are often the fi rst to sense that there may be a visual problem with a young baby. Experienced mothers tend to present their children earlier. It is important not to dismiss parental con-cerns, as this may backfi re. A useful adage is: ‘If in doubt, believe the mother and either re-examine or refer’. Even if the eyes look normal, the parents may complain of the child not fi xing or reacting appropriately to visual stimuli. There may be an obvious abnormal-ity such as a white pupillary refl ex ‘leucocoria’ or a squint. Occa-sionally family snapshots using fl ash photography show up the absence of a red refl ex and bring this to the parent’s attention.

Practical advice

If in doubt, believe the mother and either re-examine or refer.

On examination, the position and steadiness of the eyes in primary gaze is important. The presence of a persistent squint may indicate that there is an opacity of the media. It must be remembered that transient losses of binocular fi xation can be normal for the fi rst 3–4 months of life; after this age, most infants demonstrate con-sistent binocular ocular alignment over a range of stimulus dis-tances.4 Fusion in infants develops between 4.5 and 6 months of life. Any abnormal ocular movements such as nystagmus, or more rare abnormalities such as saccadomania or ‘dancing eyes’, may be indicative of a midline cerebral tumour.

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30

The presence of leucocoria (white refl ex) points to the diagnosis of cataract, primary hyperplastic vitreous or retinoblastoma. Enlargement of the globe may indicate congenital glaucoma. If there is no opacity of the media, detailed examination of the fundus, and in particular of the optic discs, is possible. Optokinetic nystag-mus is not a test that is specifi c for visual acuity, but one that is representative of the integrity of the visual system. It is normally absent in blind and severely brain-damaged children. In children with a profound visual problem, the parents often notice that the baby appears to be unresponsive to visual stimuli.

2.2.1 Electrophysiological testing

Electrophysiological testing is extremely important in the assess-ment of poor vision in neonates and children. Experience and patience are required for the acquisition of good quality results in the very young. These tests not only help to secure specifi c diag-noses, but by systematic assessment of function along the visual pathways can also localise the problem underlying the visual defects. Among children, development as well as disease can affect electrophysiological parameters (Fig. 2.1); therefore, the diagnosis of abnormality depends critically on knowledge of the normal responses for age.5 A brief description of the most common elec-trophysiology tests and their function is given below.

• Visually evoked potential (VEP) detects dysfunction of the visual pathways from the optic nerve to the visual cortex

• Electroretinography (ERG) assesses the function of the neuro-retina. Different stimuli can be used to assess the function of the rod and cone photoreceptors separately. The ERG waveform can also be used to differentiate between dysfunction in different layers of the neuroretina and is an indicator of whether the problem lies within the macular area or the optic nerve. The P50 component is representative of macular function and the N95 component of optic nerve function, although an abnormality in one may infl uence the other

• Electro-oculography (EOG) assesses the integrity of the retinal pigment epithelial (RPE) cells

The interpretation of electrophysiological data is a complex issue and must always be made with reference to the clinical fi ndings. Examples of expected electrophysiology abnormalities in inherited disorders are given below (see Table 2.2, p. 39)

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31

Figure 2.1 A, Normal waveforms for standard electrophysiology tests (a–f). The ERG represents the combined electrical activity within the retina. The ‘a’ wave represents the activity of the photoreceptors; the ‘b’ wave has its origin in the Muller (glial) cells. (a) The pattern ERG demonstrates good macular function (P50) peak and normal optic nerve function (N95) trough. Normal cone function is shown by a normal cone ERG (using a bright red fl ash) (b) and a normal 30 Hz fl icker ERG (c). Normal rod function is illustrated by a normal rod ERG tested under conditions that preferentially stimulate rod function (dim blue fl ash) (d). The maximal ERG response gives an indication of total photoreceptor function (e). The EOG waveform, which refl ects retinal pigment epithelial function, indicates a normal ‘dark to light’ rise which refl ects the comparison of amplitudes under dark and light adapted states (f).

5

0

OD

OS

–50 50

P50 max (ms) N95 max (ms) b wave max (ms)

a wave max (ms) b wave max (ms) b wave max (ms)a wave max (ms)

b wave max (ms)

100

Pattern ERG40’ check

(a) (d)

(b) (e)

(c) (f)

Rod ERGDim blue flash (subject dark adapted)

Cone ERGBright red flash

Maximal ERGBright white flash

30-Hz Flicker ERGModerate white flashes

EOGLight peak/Dark trough %

Dark adaptation/Light adaptation (min)

150 200 0 50 100 200150

0 20 40 0 5060 100 10080

0 0 5 10 15 20 25 3050 100 200150

uV

200

0

OD

OS

–200

uV500

0

0

OD

OD

OS

OS

–500

200

uV

500

0

OD

OS

–500

uV

500

0

OD

OS

–500

uV

–200

Oscillatorypotentials

P50

N95

a wave

b wave

b wave

b wave

b wave

Light peakDark trough

a wave

A

Ch002-H1815.indd 31 9/15/2006 12:06:54 PM


32

Figure 2.1 B, Electrodiagnostic tests from a patient with retinitis pigmentosa showing ‘fl at’ tracings for the maximal ERG (e), cone ERG (b) and rod ERG (d), indicating profound loss of photoreceptor function. There is also absence of the ‘light rise’ on the EOG (f). Interestingly, the patient’s central vision remains 6/9 [Log MAR 0.2] in either eye, indicating some preservation of central photoreceptors. This is confi rmed by the pattern ERG (a), which shows an abnormal but relatively preserved waveform.

5

0

RE

LE

–50 50

P50 max (ms) N95 max (ms) b wave max (ms)

a wave max (ms) b wave max (ms) b wave max (ms)a wave max (ms)

b wave max (ms)

100

Pattern ERG40’ check

(a) (d)

(b) (e)

(c) (f)

Rod ERG

Cone ERG Maximal ERG

30-Hz Flicker ERG EOG

Dark adaptation/Light adaptation (min)

150 200 0 50 100 200150

0 20 40 0 5060 100 10080

0 0 5 10 15 20 25 3050 100 200150

uV

200

0

RE

LE

–200

uV200

0

0

RE

RE

LE

LE

–200

50

50

uV

500

0

RE

LE

–500

uV

333

0

RE

LE

–333

uV

–

B

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33

2.3 Clinical scenarios

2.3.1 The neonate or young baby who appears to be visually impaired

When a baby with a suspected visual problem is presented to the ophthalmologist, important clinical signs to look for are those detailed in Section 2.2. If there appears to be a visual problem, the working differential diagnosis is as follows (this list is given in alphabetical order and is not all inclusive, as many other rare conditions exist):

• Albinism• Cerebral blindness• Congenital cataract• Congenital glaucoma• Congenital idiopathic nystagmus• High refractive error• Leber’s congenital amaurosis• Macular colobomata• Optic atrophy or hypoplasia• Primary hyperplastic vitreous• Retinoblastoma• Retinopathy of prematurity.

Retinopathy of prematurity (ROP) is unlikely in a full-term infant, but if the baby was of low birthweight or pre-term (born earlier than 37 weeks) ROP should be considered. Babies with a birthweight of less than 1500 g are at risk of ROP and should be screened rou-tinely. Total visual loss from ROP has been reported in 2–4% of babies who weigh less than 940 g.6

Examination of the optic discs may reveal the diagnostic double halo of hypoplastic discs or the normal-sized but pale discs of optic atrophy. If an intracranial tumour is present, papilloedema may be seen. The heredofamilial optic atrophies are characterised by their patterns of inheritance, and hereditary optic atrophy can present in several different ways. The clinical fi ndings and age of onset are different in each group. A simplifi ed list of the spectrum of the inherited optic atrophies is shown in Table 2.1.

The presence of leucocoria is often reported by the parents and, although the most common cause of leucocoria is cataract, retino-blastoma must always be excluded promptly. Retinoblastoma is a rare life-threatening tumour with complex genetic inheritance.

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34

Those affected demonstrate a predisposition to retinoblastoma, which can be either heritable or non-heritable. Childhood cataract, although surgically treatable, causes signifi cant visual morbidity because of associated amblyopia, even with early surgical treat-ment. Cataracts that are present at birth or become apparent in the fi rst year of life account for just under 20% of all causes of blind registration in children under the age of 15 years in England and Wales. Genetically determined cataracts are a hetero-geneous group of disorders.7 Approximately 25% of congenital cataract is inherited in an autosomal dominant manner; autosomal recessive cataract is uncommon in Britain and is more prevalent in communities where consanguinity is common. X-linked cata-racts are rare. They usually occur in isolation, although congenital cataract can be associated with other ophthalmic manifestations such as microphthalmos, glaucoma and coloboma. Congenital cataract can also be part of a systemic syndrome, of which there are many.

Congenital glaucoma occurs in 1 in 10 000 births in Western countries. Although several modes of inheritance have been documented, in most families the disorder is transmitted in an autosomal dominant manner with full penetrance. A full account of the molecular genetic details can be found at the Online Mendelian Inheritance in Man (OMIM) website (http://www.ncbi.nlm.nih.gov/omim).8 Even though the ocular globe is often enlarged at birth in congenital glaucoma owing to raised intraocular pressure in utero, an early diagnosis is advanta-geous in limiting fi eld loss and preventing increasing buphthal-mos. Evidence also exists indicating that, owing to the plasticity of the visual system, young babies may have some potential for optic nerve recovery if treated early. In the absence of a positive family history, the diagnosis can sometimes be overlooked in the early stages. Congenital glaucoma often presents with a ‘watery eye’. The crucial question on history taking is to determine whether the ‘epiphora’ was present at birth or developed later. Epiphora from nasolacrimal duct obstruction is usually not present at birth but begins when tear production becomes well established. A watery eye at birth should fl ag up the diagnosis of congenital glaucoma.

Congenital idiopathic nystagmus and macular colobomata are rare causes of poor central vision, whereas primary hyperplastic vitreous presents as an opacity in the media. High refractive errors should always be kept in mind in these cases.

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35

Ta

ble

2.1

Clin

ical

Fea

ture

s of

the

Inh

erit

ed O

ptic

Atr

ophi

es

Ju

ve

nil

e

Co

nge

nit

al

Be

hr’s

O

pti

c a

tro

ph

y

Le

be

r’s

op

tic

(i

nfa

nti

le)

(sim

ple

) sy

nd

rom

e

wit

h d

iab

ete

s

ne

uro

path

y

± d

eafn

ess

Patt

ern

of

Dom

inan

t R

eces

sive

R

eces

sive

R

eces

sive

M

itoc

hond

rial

inhe

rita

nce

inhe

rita

nce

Age

of

onse

t 4

–8

3–4

1–9

6–14

11

–30

(yea

rs)

Vis

ual l

oss

Mild

/mod

erat

e Se

vere

M

oder

ate

Seve

re

Mod

erat

e to

sev

ere,

depe

ndin

g on

the

m

utat

ion

(see

sec

tion

2.

5.1)

Fina

l vis

ual

6/12

[Lo

gMA

R 0

.3]

6/60

[Lo

gMA

R 1

.0]

6/60

[Lo

gMA

R 1

.0]

3/60

[Lo

gMA

R 1

.3]

6/60

[Lo

gMA

R 1

.0]

acui

ty

to 6

/60

to

han

d m

otio

n

to 1

/60

to 1

/60

[L

ogM

AR

1.0

]

[L

ogM

AR

1.8

] [L

ogM

AR

1.8

]

Col

our

visi

on

Blu

e/ye

llow

def

ect.

Se

vere

M

oder

atel

y se

vere

Se

vere

D

ense

cen

tral

N

ote:

if a

cqui

red

dysc

hrom

atop

sia

dysc

hrom

atop

sia

dysc

hrom

atop

sia

scot

oma

for

colo

urs

re

d/g

reen

def

ect

–

wro

ng d

iagn

osis

Nys

tagm

us

Rar

e U

sual

In

50%

N

o N

o

Opt

ic d

iscs

M

ild t

empo

ral

Mar

ked

diffu

se

Mild

tem

pora

l M

arke

d di

ffuse

D

isc

swel

ling

and

pa

llor

pallo

r pa

llor

pallo

r te

lang

iect

atic

ves

sels

in

acu

te s

tage

.

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erat

ely

diffu

se

pallo

r

Ch002-H1815.indd 35 9/15/2006 12:06:55 PM


36

Children with multiple handicaps

Children who suffer from congenital conditions such as rubella, cytomegalovirus, toxoplasmosis or fetal alcohol syndrome often have multiple handicaps that can involve hearing as well as vision. Recent studies have indicated that almost half of visually impaired children have cerebral palsy and the majority will exhibit behavioural problems (63%), learning disabilities (50%) and other sensory defi cit (hearing impairment 18%) early in childhood.9

2.3.2 The visually impaired baby with no obvious ophthalmic abnormality

If the baby is visually impaired but no obvious ophthalmological problem is detectable clinically, the following diagnoses should be strongly reconsidered and the baby re-examined. These condi-tions can be diffi cult to detect in the early stages:

• Albinism – oculocutaneous (tyrosinase positive) and ocular albinism

• Cerebral blindness• Delayed visual development• Leber’s congenital amaurosis• Optic atrophy• Optic disc hypoplasia.

In the early stages, Leber’s congenital amaurosis often shows no abnormality on fundoscopy; the optic discs, however, can some-times appear slightly pale, and early thinning of the arterioles is an important early sign in this condition. The pupillary refl exes, although sometimes normal, are often sluggish or absent. The baby is often photophobic. Electrophysiological testing is helpful for diagnostic purposes. Recently, Leber’s congenital amaurosis has been mapped to fi ve genetic loci, indicating a spectrum of disease manifestation or phenotypic variation. Exact details can

Practical advice

As epiphora from nasolacrimal duct obstruction is usually not present at birth but begins when tear production becomes well established, a watery eye at birth should fl ag up a diagnosis of congenital glaucoma.

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37

be located on the OMIM website.8,10 Leber’s amaurosis is listed as disorder no. 204000.

Optic disc hypoplasia can be subtle and is easily missed unless specifi cally looked for with the direct ophthalmoscope. Compari-son of the optic disc size with the large aperture on the ophthal-moscope can be useful in diagnosing optic disc hypoplasia. Indirect ophthalmoscopy alone is not suffi ciently sensitive to pick up hypoplasia of the optic disc. Other helpful signs include the presence of nystagmus, sluggish pupillary refl exes and the char-acteristic optic disc double ring sign.

Practical advice

The large target on the Welch Allyn direct ophthalmoscope is the same size as an average optic disc.

Cerebral blindness manifests with normal ophthalmic fi ndings, including the presence of normal pupillary refl exes. In cerebral blindness, the electroencephalogram (EEG) is abnormal; the baby often has other signs of developmental delay and may have midline defects including cleft lip or palate.

Albinism can be very evident and a family history may be present, although the signs can be subtle in tyrosinase-positive ocular albi-nism. The pupillary refl exes are normal, as are the optic discs, but the baby may be photophobic. Iris transillumination is present, but may be diffi cult to elicit in a young baby using the slit lamp. The fundus will appear albinotic or blond.11

Practical advice

An easy way of detecting iris transillumination in a baby is to place the transilluminator from the ophthalmoscope on the lower lid in a darkened room. Iris defects will be seen easily.

Delayed visual development involves no ophthalmological or electro-physiological abnormality. The baby is often premature or small for dates (smaller than the expected weight for age). Except in children with multiple handicaps, it is unusual for delay to persist

Ch002-H1815.indd 37 9/15/2006 12:06:55 PM


38

beyond the age of 4 months.12 Although the prognosis for vision is generally good, a small proportion of patients are left with a resid-ual defi cit. The electrophysiological fi ndings in the conditions described above are summarised in Table 2.2.

2.3.3 The child with visual diffi culty

History and examination

These children have usually been normally sighted in infancy and have thus had a relatively normal early educational history. Prob-lems usually become apparent late in the fi rst decade. During the early years of primary school, these children begin to have pro-gressive problems with seeing the blackboard and subsequently with small print and low contrast material. In this age group a history of the visual symptoms and a positive family history of inherited conditions may also be present. Children with decreased distance acuity with good near acuity may simply be myopic. The normally sighted myope will, however, use a conventional near working distance, whereas the visually impaired myopic child will tend to hold things closer than expected.

Other details on history taking that can be helpful include the following. Children suffering from optic atrophy complain of reducing vision but usually have no other specifi c symptoms. Those suffering from cone dystrophies, however, characteristically complain of intense photophobia and diffi culty with colour vision.

Practical advice

Interestingly, patients with cone dystrophy may remark that their visual acuity is better in dim lighting. Visual acuity can increase by two to three lines in mesopic conditions.

The parents of children with early-onset retinitis pigmentosa may report night blindness or restriction of fi elds, which is often mani-fested as clumsiness.

Parents who suffer from retinitis pigmentosa are often acutely sensitive to the presence of night blindness in their children. In retrospect, when asked, people with retinitis pigmentosa will admit to having been night blind from as far back as they can remember.

Ch002-H1815.indd 38 9/15/2006 12:06:55 PM


39

Ta

ble

2.2

Inh

erit

ance

Pat

tern

s, V

isua

l Pro

gnos

is, V

isua

l Fie

ld L

oss

and

Elec

trop

hysi

olog

ical

Fin

ding

s in

Inh

erit

ed D

isea

ses

In

he

rita

nce

Vis

ual

VE

R

ER

G

EO

G

Vis

ual

Vis

ual

p

att

ern

p

rogn

osi

s

fi e

ld

aid

s

de

fects

Lebe

r’s

AR

Ve

ry p

oor

Low

am

plit

ude

Unr

ecor

dabl

e U

sual

ly

Com

plet

e lo

ss

Req

uire

vis

ion

amau

rosi

s

<6/

60

or a

bsen

t

abno

rmal

of

fi e

ld

subs

titu

tion

[Log

MA

R 1

.0]

tech

niqu

es

to

PL

Opt

ic a

tro

phy

AD

, AR

or

Var

iabl

e R

educ

ed b

ut

N95

N

orm

al

Para

cent

ral

Goo

d w

ith

X

-lin

ked

6/12

de

pend

s on

co

mpo

nent

scot

omas

LV

As

[Log

MA

R 0

.3]

type

ab

norm

ala

to h

and

mot

ion

Opt

ic d

isc

Spor

adic

G

ood

or p

oor,

Late

ncie

s N

95

Nor

mal

V

aria

ble

Vis

ual a

ids

hypo

plas

ia

un

ilate

ral o

r no

rmal

; co

mpo

nent

us

eful

if

visu

al

bi

late

ral

ampl

itud

es

abno

rmal

a

ac

uity

poo

r

abno

rmal

Cer

ebra

l Sp

orad

ic

Poor

D

imin

ishe

d N

orm

al

No

rmal

D

iffi c

ult

to

No

t go

od

wit

hbl

indn

ess

or a

bsen

t

te

st

LVA

s. N

eed

en

viro

nmen

tal

m

odifi

cati

on.

Del

ayed

vis

ual

Spor

adic

N

orm

al v

isio

n N

orm

al

Nor

mal

N

orm

al

Nor

mal

G

oo

d w

ith

deve

lopm

ent

of

ten

deve

lops

LV

As

and

tr

aini

ng w

hen

ol

der

Ch002-H1815.indd 39 9/15/2006 12:06:55 PM


40

Ta

ble

2.2

Inh

erit

ance

Pat

tern

s, V

isua

l Pro

gnos

is, V

isua

l Fie

ld L

oss

and

Elec

trop

hysi

olog

ical

Fin

ding

s in

Inh

erit

ed

Dis

ease

s—co

nt’d

In

he

rita

nce

Vis

ual

VE

R

ER

G

EO

G

Vis

ual

Vis

ual

p

att

ern

p

rogn

osi

s

fi e

ld

aid

s

de

fects

Alb

inis

m

AR

, X-l

inke

d V

aria

ble

Flas

h V

ER

Supe

rnor

mal

Su

pern

orm

al

Func

tio

nally

G

ood

wit

h

6/

18

norm

al;

ERG

sco

topi

c

norm

al

dist

ance

LV

As

[Log

MA

R 0

.5]

patt

ern

VER

b-

wav

e

to

6/6

0 va

riab

le

[L

ogM

AR

1.0

]

Star

gard

t’s

AR

50

% t

o go

od

Nor

mal

U

sual

ly

Nor

mal

C

entr

al

Goo

d w

ith

dise

ase

or

50

% t

o <

6/60

norm

al; 2

0%

earl

y,

scot

oma

LVA

sfu

ndus

[Log

MA

R 1

.0]

of

cas

es m

ild

decr

ease

dfl a

vim

acul

atus

b-w

ave

loss

la

ter

Con

e

AR

, X-l

inke

d Po

or

Nor

mal

Ph

otop

ic

Usu

ally

C

entr

al

Goo

d w

ith

red

dyst

roph

y

6/24

resp

ons

e no

rmal

sc

oto

ma;

ti

nted

lens

es

[L

ogM

AR

0.6

]

abno

rmal

;

norm

al

to

6/6

0

scot

opi

c

peri

pher

al

[L

ogM

AR

1.0

]

resp

onse

fi eld

s

no

rmal

Patt

ern

AD

U

sual

ly g

ood

Nor

mal

N

orm

al

Abn

orm

al

Nor

mal

/cen

tral

U

sual

ly n

otdy

stro

phy

6/

6

scot

om

a ne

eded

[Log

MA

R 0

.0]

to 6

/18

[Log

MA

R 0

.5]

Ch002-H1815.indd 40 9/15/2006 12:06:56 PM


41

Ta

ble

2.2

Inh

erit

ance

Pat

tern

s, V

isua

l Pro

gnos

is, V

isua

l Fie

ld L

oss

and

Elec

trop

hysi

olog

ical

Fin

ding

s in

Inh

erit

ed

Dis

ease

s—co

nt’d

In

he

rita

nce

Vis

ual

VE

R

ER

G

EO

G

Vis

ual

Vis

ual

p

att

ern

p

rogn

osi

s

fi e

ld

aid

s

de

fects

Bes

t’s d

isea

se

AD

Po

or

Nor

mal

N

orm

al

Abn

orm

al

Nor

mal

/cen

tral

V

aria

ble

6/60

scot

om

a re

spon

se

[L

ogM

AR

1.0

]

Ret

init

is

AD

, AR

or

A

R, X

-lin

ked

Abn

orm

al

Abn

orm

al t

o A

bnor

mal

Pe

riph

eral

G

ood

wit

hpi

gmen

tosa

X

-lin

ked

poor

; AD

bet

ter

ex

ting

uish

ed

co

nstr

icti

on ±

C

CT

Vs

3/60

cent

ral d

efec

ts

[L

ogM

AR

1.3

]

to

NPL

X-l

inke

d X

-lin

ked

Poor

N

orm

al

Nor

mal

N

orm

al

Cen

tral

and

G

ood

wit

hre

tino

schi

sis

6/

36

a-

wav

e;

pe

riph

eral

LV

As

[Log

MA

R 0

.8]

re

duce

d

scot

om

as

to

3/6

0

scot

opi

c

[Log

MA

R 1

.3]

b-

wav

e

Gyr

ate

atro

phy

AR

Po

or

Nor

mal

Ex

ting

uish

ed

Abn

orm

al

Con

stri

cted

G

ood

wit

h

<

6/60

wit

h sc

otom

as

CC

TV

s

[L

ogM

AR

1.0

]

by

age

40

a The

N95

com

pone

nt o

f th

e ER

G d

enot

es o

ptic

ner

ve d

ysfu

ncti

on. A

D, a

utos

omal

dom

inan

t; A

R, a

utos

omal

rec

essi

ve; C

CT

V, c

lose

d ci

rcui

t te

levi

sion

; LV

A, l

ow v

isio

n ai

d; N

PL, n

o pe

rcep

tion

of

light

; PL,

per

cept

ion

of li

ght;

VER

, vis

ually

evo

ked

resp

onse

; EO

G, e

lect

ro-o

culo

grap

hy;

ERG

, ele

ctro

reti

nogr

aphy

.

Ch002-H1815.indd 41 9/15/2006 12:06:56 PM


42

Other cardinal clinical signs include the status of the optic discs and retinal vasculature, the presence of intraretinal pigment depo-sition, and the pattern and distribution of retinal deposits. During the clinical examination it is important not to omit colour vision testing. It is necessary to use a method that can detect yellow/blue defects, as well as the more common red/green defect.

A test that is rapid and user friendly in this age group is the City University plates or the D15, which is more convenient for children. A Jumbo D15 is available for use with visually impaired children.

2.4 Ophthalmic disorders presenting in childhood

The disorders that are most prevalent in this age group are:

• Best’s disease or vitelliform dystrophy• Cone dystrophy• Optic atrophy• Retinitis pigmentosa• Stargardt’s disease or fundus fl avimaculatus• X-linked retinoschisis.

The pattern of visual loss varies with each condition, and some-times even within each disorder there can be signifi cant variation in disease progression because of genetic heterogeneity, that is, different mutations in different genes that give similar fundal appearances. A good example is retinitis pigmentosa. In optic atrophy vision may reach a stable level in childhood, whereas in the retinal dystrophies visual loss is progressive and can take 20 years to reach a level of signifi cant impairment.

Optic atrophy can be inherited in several different ways, each type demonstrating slightly different clinical onsets and signs, the details of which can be found in Table 2.1.

Vitelliform dystrophy or Best’s disease presents with a yellow egg-yolk deposit, usually centred on the macula. The deposit can be identi-fi ed shortly after birth or may develop later. It is described as a ‘sunnyside up’ egg and measures approximately two to three disc areas in diameter. Although the lesion is present early in life, the central vision can remain good until late in the fi rst or early in the second decade, when there is progressive loss of central vision associated with disintegration of the ‘yolk’. Visual deterioration is

Ch002-H1815.indd 42 9/15/2006 12:06:56 PM


43

slow but progressive to a level of around 6/60 [LogMAR 1.0]. Occasionally the lesion becomes vascularised by choroidal vessels, at which stage the vision usually drops dramatically and the prog-nosis becomes much worse. A mutation in the bestrophin gene on chromosome 11 (VMD2; OMIM no. 607854) has been shown to cause Best’s disease.8,13

Stargardt’s disease or fundus fl avimaculatus Clinically these patients demonstrate ‘fi sh-tail’ fl ecks in the fundus (Plates 1 & 2 [Fig. 2.2]). These fl ecks are characteristically located centrally in the fundus in Stargardt’s disease and more peripherally in fundus fl avimacu-latus. It is thought that these two clinical phenotypes are part of the same clinical spectrum. In Stargardt’s disease, areas of retinal thinning and atrophy may accompany the fl ecks. The patient pre-senting with a ‘fl ecked retina’ is fairly common in clinical practice, and the differential diagnosis is shown in Figure 2.3. Recently, several genetic loci have been mapped for both autosomal reces-sive and dominant Stargardt’s disease.8,14

Cone dystrophy These patients characteristically complain of reduced vision and photophobia, and on clinical examination show defects of colour vision. Fundoscopy is often of little help as the changes can be very subtle. Electrophysiological testing is invaluable in making the diagnosis. These patients may respond positively to ‘red fi lter’ lenses, which prevent rod bleaching. The disorder may be inherited in an autosomal dominant, recessive or X-linked manner. Several chromosomal locations have been linked to this heterogeneous group of diseases.15

X-linked retinoschisis is a fairly common disorder inherited by males from their mothers, who are asymptomatic carriers. Recent work has shown that the gene responsible for this disease is located on the short arm of the X chromosome in the Xp22 region.16 The con-dition occurs almost exclusively in boys. Owing to the subtlety of the clinical signs, the diagnosis can be diffi cult to make and the pathognomonic clinical sign of foveal retinoschisis is present in only 50% of cases. Clinically the foveal area appears optically empty with radial folds in the superfi cial layer. Silver–grey spots can be found throughout the retina, with lattice changes in the periphery. A high index of suspicion is required for prompt diag-nosis. Cases that are not clinically obvious will show the charac-teristic electrophysiological change of a subnormal b-wave on ERG.

Ch002-H1815.indd 43 9/15/2006 12:06:56 PM


44

Fig

ure

2.3

D

iffer

enti

al d

iagn

osis

of

a pa

tien

t pr

esen

ting

wit

h a

‘fl ec

ked’

ret

ina.

AD

, aut

osom

al d

omin

ant;

AR

MD

, ag

e-re

late

d m

acul

ar d

egen

erat

ion;

CN

VM

, cho

roid

al n

eova

scul

ar m

embr

ane;

EO

G, e

lect

ro-o

culo

grap

hy; E

RG

, el

ectr

oret

inog

raph

y; G

A, g

eogr

aphi

c at

roph

y; V

A, v

isua

l acu

ity.

THE

FLEC

KED

RET

INA

No

nyct

alop

iaN

ycta

lopi

aw

hite

ova

l/rou

nd re

gula

r dep

osits

Cry

stal

line

retin

opat

hies

Rou

nd y

ello

wde

posi

ts a

ndpi

gmen

tary

cha

nges

Irreg

ular

line

arfis

h-ta

il fle

cks

Prog

ress

ive

field

loss

Prog

ress

ive

nyct

alop

iaO

ptic

dis

c pa

llor

Atte

nuat

ed v

esse

lsER

G/E

OG

ext

ingu

ishe

dPo

or V

A

Nor

mal

fiel

dsSt

atio

nary

nyc

talo

pia

Nor

mal

dis

csN

orm

al v

esse

lsER

G/m

ore

abno

rmal

with

dar

k ad

apta

tion

Goo

d VA

Ova

l fle

cks

Poor

VA

Very

sm

all f

leck

sIrr

egul

arla

rge

fleck

s

Ret

initi

spu

ncta

taal

besc

ens

Auto

som

alre

cess

ive

inhe

ritan

ce

Fund

usal

bipu

ncta

tus

Auto

som

alre

cess

ive

inhe

ritan

ce

Flec

ked

retin

a of

Kand

ori

Auto

som

alre

cess

ive

inhe

ritan

ce

Age

20–5

0Le

sion

s na

sal t

o di

sc

Age

>55

CN

VMG

A

Mac

ula

norm

alM

acul

abr

onze

-bea

ten

appe

aran

ce

Fund

usfla

vim

acul

atus

Auto

som

alre

cess

ive

inhe

ritan

ce

Star

gard

t’sdi

seas

eAu

toso

mal

rece

ssiv

eAu

toso

mal

dom

inan

tin

herit

ance

Her

edita

rydo

min

ant

drus

enAu

toso

mal

dom

inan

t in

herit

ance

MD

Com

plex

inhe

ritan

ce

• Bi

ette

’s (A

D)

as

ympt

omat

ic

visu

al lo

ss a

nd

nyct

alop

ia o

nly

ve

ry la

te

• Pr

imar

y an

d

seco

ndar

y

oxal

osis

• Ta

mox

ifen

re

tinop

athy

us

ually

as

ympt

omat

ic

Ch002-H1815.indd 44 9/15/2006 12:06:56 PM


45

Retinitis pigmentosa. Although the clinical signs of retinitis pigmen-tosa will already be well established in affected children in this age group, due to the fact that central visual acuity generally remains unimpaired until late in the course of the condition, chil-dren who have retinitis pigmentosa but a negative family history are often not diagnosed until much later in life, often not until the second or third decade. Retinitis pigmentosa has been studied extensively at the molecular level17 and is a disorder with extreme genotypic and phenotypic variation. The clinical fi ndings are discussed on page 47.

Usher’s syndrome accounts for 15–20% of cases of retinitis pigmen-tosa. It is associated with deafness and accounts for 50% of deaf–blindness. Usher’s syndrome is clinically heterogeneous, with several subtypes being recognised (Table 2.3).18

Table 2.3 Subtypes of Usher’s Syndrome

Type Description

I Profound congenital deafness with onset of retinitis pigmentosa by age 10 years. Impairment of vestibular refl exes and clinically evident ataxia are more frequently found in this group

II Moderate to severe congenital deafness with onset of retinitis pigmentosa in late teens

III Retinitis pigmentosa fi rst noted at puberty, with progressive hearing loss

Practical advice

When an adult or older child presents with Usher’s syndrome, it is possible to discriminate between type I and type II by the patient’s speech. Type I sufferers, who have profound congenital deafness, have abnormal speech. These patients may also be ataxic, displaying signs of poor coordination. Those with Usher’s syndrome type II have normal speech patterns.

Usher’s syndrome is commonly misdiagnosed or diagnosed late. It is important to ask about hearing impairment in all patients with retinitis pigmentosa.

Ch002-H1815.indd 45 9/15/2006 12:06:56 PM


46

2.5 The adolescent with deterioration in vision

Many adolescents with impaired vision have had the condition diagnosed in childhood and are reviewed purely to assess their requirement for visual aids and to provide them and their family with support and information, and genetic counselling if requested. Some teenagers, however, develop problems at this stage. In this age group, visual functions are assessed in the same manner as in the adult presenting with visual loss. Extra care and attention must be given to specifi c problems experienced in education, and care must be taken in the provision of realistic career advice.

2.5.1 Disorders presenting in adolescence

Conditions that can start to become symptomatic in this age group include:

• Best’s disease or vitelliform dystrophy• Cone dystrophy• Leber’s optic neuropathy• Retinitis pigmentosa• Stargardt’s disease or fundus fl avimaculatus.

Leber’s hereditary optic neuropathy (LHON) was originally described in 1871 by Theodore Leber. Clinically, the disease presents with acute visual loss, circumpapillary telangiectatic microangiopathy, tortu-osity of the retinal vessels and oedema of the retinal nerve fi bres. The disease is transmitted from mother to child, with 85% of those affected being male. Visual loss usually develops between the ages of 11–30 years, but a range of 6–62 years has been described. Recent advances in the fi eld of molecular genetics have yielded insights into the underlying aetiology of this disease. LHON is associated with several different point mutations (spelling mistakes in the genetic code) of mitochondrial DNA that appear to be pathogenic for the disease. These are known as the 3460, the 11778, the 14484 and the 15257 mutations, with the 11778 mutation accounting for more than 70% of cases. Interestingly, patients with the 14484 mutation have a substantially better outcome than those with other mutations, with a fi nal visual acuity of 6/24 [LogMAR 0.6] in 71% of cases.19 It has also been reported that, in many patients with LHON, the severity of the disease is related to tobacco smoking. Increased cyanocobalamin and cyanide blood levels in patients support this hypothesis.

Ch002-H1815.indd 46 9/15/2006 12:06:56 PM


47

Retinitis pigmentosa often presents in this age group. It is a hereditary degeneration primarily involving the photoreceptors of the retina with secondary changes in the retinal pigment epithelium and the neurosensory retina. There is an associated migration of pigment from the pigment epithelium into the retina, attenuation of the retinal vessels and atrophy of the optic nerve (Fig. 2.4 A & B [Plates 3 & 4]). The symptoms are night blindness, reduced peripheral vision (‘tunnel’ vision) and ultimately decreased central vision. This condition is inherited in a dominant, recessive or X-linked fashion, and can appear at any age. Genetic counselling is essential and recent advances in the understanding of the molecular genet-ics of retinitis pigmentosa will make genetic counselling more accurate. It has now become evident that the traditional classifi ca-tion of three types of retinitis pigmentosa (autosomal dominant, recessive and X-linked) is an oversimplifi cation, as there are numerous mutations in approximately 30 different retinal genes causing a phenotypically similar disease.17 This also explains why many patients have different symptoms and disease progression. Although many patients suffer from peripheral visual loss early in the disease, some notice central scotoma and loss of colour vision fi rst. The clinical prognostic factors important in retinitis pigmentosa are the age at onset of problems and the inheritance pattern. Patients with recessive and X-linked types tend to lose function and independence earlier, whereas those with an autoso-mal dominant condition tend to maintain fairly good vision until middle age.

Practical advice

In the clinical setting, bilaterally swollen discs associated with a sudden reduction of vision are unlikely to represent papilloedema.

Practical advice

Probably the most valuable piece of information is the pattern of visual loss in members of the same family in previous generations. Retinitis pigmentosa tends to run true to form within a particular family.

Ch002-H1815.indd 47 9/15/2006 12:06:56 PM


48

A

BFigure 2.4 (Plates 3 & 4) Advanced retinitis pigmentosa with extensive retinal pigmentary changes, vascular attenuation and optic disc pallor (A, right eye, B, left eye).

Ch002-H1815.indd 48 9/15/2006 12:06:57 PM


49

Although a pigmentary retinopathy is usually due to isolated reti-nitis pigmentosa with no associated systemic disease, it should be remembered that it may be part of a more generalised neurological disorder. Two rare but important systemic diseases are abetali-poproteinaemia (Bassen–Kornzweig syndrome) and Refsum’s disease. The importance of these diagnoses lies in the fact that it is possible to limit the amount of visual loss by treatment if they are recognised early.

Refsum’s disease is an autosomal recessively inherited disorder, which presents with nyctalopia (night blindness), distal sen-sory loss and weakness, anosmia (loss of smell) and deafness.

CFigure 2.4 C (Plates 3 & 4) The corresponding ‘binocular Estermann’ fi elds show reduction of the visual fi eld to less than 50° on the horizontal and less than 20° on the vertical meridians, rendering the patient ineligible for driving. Black rectangles indicate loss of function.

Ch002-H1815.indd 49 9/15/2006 12:07:01 PM


50

Ophthalmic manifestations include corneal opacifi cation, cataract, glaucoma, pigmentary retinopathy and optic atrophy. Treatment includes strict elimination of phylol from the diet (primarily leaf vegetables, butter and animal fats).

Abetalipoproteinaemia (Bassen–Kornzweig syndrome) is inherited in an autosomal dominant fashion. This disease presents with nyctalo-pia, neuromuscular disability and dietary fat intolerance. A pro-gressive spinocerebellar ataxia and retinopathy occur secondary to poor absorption of vitamin E. Treatment is with large doses of oral vitamin E in addition to a low fat diet and supplements of the other fat-soluble vitamins.

Other conditions Although patients with Best’s disease, Stargardt’s disease and cone dystrophy may experience mild problems in early childhood, the condition often remains undiagnosed until visual acuity begins to fall in the early teens. Symptoms are often mild and, in the event of there being no family history, the condi-tion goes unnoticed as the child may naturally compensate well by adjusting working distances, for instance by moving closer to the blackboard.

2.6 Low vision aids

2.6.1 Use of low vision aids

Although the possibility of treatment for these disorders at present is virtually non-existent, the ophthalmologist and optometrist play a key role in providing the aids and services that help make these patients functional. The exception, however, is those with bilateral congenital cataracts who, if detected early and operated on soon afterwards, can achieve relatively normal levels of dis-tance acuity through contact or intraocular lenses. One of the most important decisions for the parent of a young child is whether education will be possible in the normal schooling system. The availability of low vision aids and appropriate educational support is of paramount importance. Children and young adults are more dexterous than older adults with visual impairment, and with encouragement can utilise low vision aids very successfully. It is important that the introduction of visual aids is carried out in a non-threatening manner, and in the younger child may even be introduced as a game. The earlier the age of onset and the more

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severe the degree of visual loss, the more educational progress is impeded. It is the authors’ experience that most children with mild to moderate visual impairment can cope in normal school, given the following provisions:

• Good parental understanding of the problem• Teaching and advisory peripatetic support• A bright and dextrous child.

2.6.2 Practicalities of usage of low vision aids by children

1 Phakic children with an acuity greater than 6/60 [LogMAR 1.0] generally prefer to utilise reduced working distances and increase accommodation to tackle short- to medium-term near vision tasks. As demands increase and accommodation lags, low visual aids have to be used more routinely. Dome magnifi ers are often the aid of choice for albinos and those with congenital nystagmus.

2 Aphakic children require higher levels of magnifi cation and benefi t from stand magnifi cation (×3 to ×12) or spectacle magnifi ers (single vision or bifocal). Low vision aids must be used in conjunction with a spectacle or contact lens distance correction.

3 Children with retinitis pigmentosa and central visual loss benefi t from closed circuit televisions (CCTVs) and, as they get older, special software that they can utilise with a personal computer thus gaining access to on-screen enlargement and speech conversion.

4 Distance low vision aids can be used by virtually all school-aged visually impaired children, although there is sometimes resistance to use these in the public domain. The children should be encouraged to enjoy the device and consider it as a leisure appliance as well as an educational device.

It is important to remember that the older child or young adult who is diagnosed as having a serious visual problem may have the added psychological adjustment of adopting a modifi ed life-style and career choice. Career plans may have to be altered, the patient may come suddenly to the understanding that driving will now not be an option when he or she comes of age, and sometimes the driving licence must be surrendered having often just been acquired. This is tragic for those who are already in employment,

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particularly if they depend on driving for their livelihood. There is no legal requirement for the use of a pushbike. Common sense and caution should prevail, and advice to parents of children should err on the side of caution.

Practical advice

For patients who have good visual fi elds but do not meet the driving criteria, the suggestion of a pushbike is a practical consideration. However, great care needs to be taken by the patient.

2.7 Recent advances in understanding the molecular genetics of inherited retinal dystrophies

The past 3–4 years have seen exciting advances in the understand-ing of the underlying genetics of many of the inherited ocular diseases. These advances are the scientifi c foundation of potential therapies for the future. Molecular genetic research is time con-suming, expensive and often frustrating. Often, even when the genetic location of a disease is located on the human genome map, the benefi ts of this small piece of information are not obvious immediately. The best way to illustrate the potential future bene-fi ts of this type of discovery is by an example in which patients with a particular type of rare macular degeneration – Sorsby’s macular dystrophy – have already derived clinical benefi t.

Sorsby’s macular dystrophy is an autosomal dominant macular degeneration developing in the third or fourth decade. Patients lose central vision from subretinal neovascularisation and atrophy of the choriocapillaris, pigment epithelium and retina. Recently, the disease-causing gene for this disorder was linked to chromo-some 22, and the causative gene identifi ed. Following identifi ca-tion of the gene, a hypothesis of the cause of progressive visual loss was postulated and, based on the known facts, an experimen-tal treatment was tried. Vitamin A at 50 000 IU per day was admin-istered orally. Within a week, the night blindness disappeared in patients at an early stage of disease. Nutritional night blindness is thus part of the pathophysiology of this genetic disease, and vitamin A supplementation can lead to a dramatic restoration of photoreceptor function. The possibility of accurate genetic testing also allows for more accurate and earlier genetic counselling.

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Interestingly, Sorsby’s macular dystrophy shares some striking clinical features with age-related macular degeneration, the most common cause of blindness in Western countries, thereby possibly providing a valuable genetic model for this disease.20

Recent advances in the understanding of the molecular basis of retinitis pigmentosa have begun to direct research into therapies for the future. An example of this comes from Berger et al,21 who published a 1-year follow-up of eight patients who underwent adult human photoreceptor transplantation as treatment for advanced retinitis pigmentosa. These authors concluded that, although allogeneic adult human photoreceptor transplantation is feasible, the process was not associated with rescue of central vision or a delay in visual loss. However, they stated that any pos-sible slowing in the rate of retinal degeneration would take many years to determine.

A gene therapy trial on the natural canine model for Leber’s amaurosis has also shown that gene therapy is successful in restor-ing navigational vision for 2 years.22 Human clinical trials involv-ing gene therapy will begin in 2006/7 for Leber’s amaurosis patients living in the UK and the USA.

Advances in the genetic understanding of ophthalmic diseases have been prolifi c in the past 10 years. The available information is now so abundant that a simplifi ed list of genetic loci would not be useful. Up-to-date information on advances in this fi eld can be found in review articles by Alan Bird23 and Dean Bok.24 Compre-hensive information on the inherited dystrophies can also be found on the RetNet website (http://www.sph.uth.tmc.edu/Retnet/).25

2.8 Summary

Children presenting with visual impairment present a special challenge in terms of diagnosis and management. Pitfalls for the unwary include diagnoses that may manifest few clinical signs. It is always wise to heed the worries of the parents, as they may suspect a problem early on. Children, even if quite severely visu-ally compromised, can show great versatility and dexterity, and often use visual aids to their best advantage.

References

1. Foster A, Gilbert C. Epidemiology of childhood blindness. Eye 1992; 6:173–176.

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2. Larsen JS. The sagittal growth of the eye: IV. Ultrasonic measurement of the axial length of the eye from birth to puberty. Acta Ophthalmologica 1971; 49:873–886.

3. Banks MS. Infant refraction and accommodation. International Ophthalmology Clinics 1980; 20:205–232.

4. Aslin RN, Dumais ST. Binocular vision in infants: a review and theoretical framework. Advances in Child Development and Behavior 1980; 15:53–94.

5. Woodruff SA, Fraser S, Burton LC, Holder GE, Sloper JJ. Evaluation of the electrodiagnostic investigation of children using the Greenwich Grading System. Eye 2004; 18:15–19.

6. Phelps DL. Retinopathy of prematurity. Pediatrics in Review 1995; 16:50–56.

7. Francois J. Genetics of cataract. Ophthalmologica 1982; 184:61–71. 8. Online Mendelian Inheritance in Man™ (OMIM™). Online.

Available: http://www.ncbi.nlm.nih.gov/omim 9. Flannagan NM, Jackson AJ, Hill AE. Visual impairment in

children: insight from a community based survey. Child Health Care and Development 2003; 29:493–499.

10. Camuzat A, Dollfus H, Rozet JM et al. A gene for Leber’s congenital amaurosis maps to chromosome 17p. Human Molecular Genetics 1995; 4:1447–1452.

11. Witkop CJ Jr. Albinism. In: Harris H, Hirschhorn K, eds. Advances in human genetics, Vol. 2. New York: Plenum Press; 1971:61–142.

12. Tresidder J, Fielder AR, Nicholson J. Delayed visual maturation: ophthalmic and neurodevelopmental aspects. Developmental Medicine and Child Neurology 1990; 32:872–881.

13. Stone EM, Nichols BE, Streb LM, Kimura AE, Sheffi eld VC. Genetic linkage of vitelliform macular degeneration (Best’s disease) to chromosome 11q13. Nature Genetics 1992; 1:246–250.

14. Kaplan J, Gerber S, Larget-Piet D et al. A gene for Stargardt’s disease (fundus fl avimaculatus) maps to the short arm of chromosome 1. Nature Genetics 1993; 5:308–311.

15. Michaelides M, Hunt DM, Moore AT. The cone dysfunction syndromes. British Journal of Ophthalmology 2004; 88:291–297.

16. Sieving PA, Bingham EL, Roth MS et al. Linkage relationship of X-linked juvenile retinoschisis with Xp22.1-p22.3 probes. American Journal of Human Genetics 1990; 47:616–621.

17. van Soest S, Westerveld A, de Jong PT, Bleeker-Wagemakers EM, Gergen AA. Retinitis pigmentosa: defi ned from a molecular point of view. Survey of Ophthalmology 1999; 43:321–334.

18. Otterstedde CR, Spandau U, Blankenagel A, Kimberling WJ, Reisser C. A new clinical classifi cation for Usher’s syndrome based on a new subtype of Usher’s syndrome type I. Laryngoscope 2001; 111:84–86.

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19. Riordan-Eva P, Sanders MD, Govan GG, Sweeney MG, Da Costa J, Harding AE. The clinical features of Leber’s hereditary optic neuropathy defi ned by the presence of a pathogenic mitochondrial DNA mutation. Brain 1995; 118:319–337.

20. Jacobson SG, Cideciyan AV, Regunath G et al. Night blindness in Sorsby’s fundus dystrophy reversed by vitamin A. Nature Genetics 1995; 11:27–32.

21. Berger AS, Tezel TH, Del Priore LV, Kaplan HJ. Photoreceptor transplantation in retinitis pigmentosa: short-term follow-up. Ophthalmology 2003; 110:383–391.

22. Bennett J. Gene therapy for Leber congenital amaurosis. Novartis Foundation Symposium 2004; 255:195–202, discussion 202–207.

23. Bird AC. What should a clinician know to be prepared for the advent of treatment of retinal dystrophies? Novartis Foundation Symposium 2004; 255:85–90, discussion 90–94.

24. Bok D. Gene therapy of retinal dystrophies: achievements, challenges and prospects. Novartis Foundation Symposium 2004; 255:4–12, discussion 12–16, 177–178.

25. Retinal Information Network (RetNet™). Online. Available: http://www.sph.uth.tmc.edu/Retnet/

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Many of the conditions causing visual loss in persons of working age are not exclusive to this age group and have therefore been described elsewhere. Visually impaired persons in this age group may, however, reach a critical stage in their disease process and therefore experience signifi cant changes in visual function with resulting changes in circumstances and/or employment. The con-ditions described in this chapter are those that cause unexpected visual compromise in the previously normally sighted adult.

3.1 Diabetic retinopathy

3.1.1 Clinical presentation

Patients with diabetes mellitus may develop none, some or all of the following retinal changes throughout life: microaneurysms, dot and blot haemorrhages, venous dilatation, venous beading and loops, hard exudate formation, cotton-wool spots, vascular occlusion, vasoproliferation, vitreous haemorrhage and tractional retinal detachment. Although dilatation of the retinal veins is the earliest clinical sign of diabetic retinopathy, this can be diffi -cult to detect on ophthalmoscopy. The earliest easily detectable sign of diabetic retinopathy is the appearance of a few tiny red dots in the retina; histological studies have shown these to be microaneurysms.

56

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Visual impairment in the working age personGiuliana Silvestri

333

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3Visual impairment in the working age person 33

57

Practical advice

The earliest clinical changes – microaneurysms – are usually found in the area of retina just temporal to the macula. This is the vascular ‘watershed’ zone.

The temporal macular area represents a watershed zone, where the medial and lateral posterior ciliary arteries meet; this is an area of potential vascular weakness. In health, the retinal capillary walls contain pericyte cells, which are responsible for maintaining tone in the capillary walls. Death of the pericytes is the fi rst histological change in diabetic retinopathy and is responsible for the formation of outpouchings of the capillary walls, known as microaneurysms.1 Once the pericytes are lost, the endothelial cells also lose their tight junctions and leakage of blood and protein into the retina occurs. Microaneurysms and small punctate haemorrhages cause no symp-toms as long as the central fovea remains uninvolved. Microaneu-rysms are particularly obvious on fl uorescein angiography and are easily distinguished from punctate haemorrhages owing to differ-ing angiographic features. The retinopathy may remain stable for many years with minor background changes or, alternatively, pro-gression may occur. Macular oedema is the commonest cause of impaired visual acuity in patients with early diabetic maculopathy. Intraretinal oedema, particularly when minor in nature, does not change the retinal transparency and is diffi cult to recognise by monocular ophthalmoscopy. A stereo view is required to detect clinically signifi cant macular oedema (CSMO). In the clinical setting, use of the simple macular photostress recovery test is helpful in deciding whether CSMO is a possibility.

Practical advice

The superfi eld non-contact Volk lens affords the observer a wide-angled stereo view of the posterior pole and peripheral retina, and is useful in the diagnosis of diabetic retinopathy and, in particular, CSMO. The resolution of the lens can be enhanced using a contact lens adaptor.

Deposits of hard yellowish-white material are frequently seen at the periphery of oedematous areas; these represent lipid and/or

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protein that has ‘precipitated out’ from the oedematous fl uid (hard exudates). Unfortunately, these changes characteristically occur in the posterior pole near the macula and can cause loss of central vision. As the disease progresses, other features become apparent on ophthalmoscopy. Cotton-wool spots, which represent areas of focal ischaemia and further dilatation and beading of the retinal veins, indicate progression of retinopathy. The mechanism whereby this occurs is obscure, but is probably related to hypoxia and venous stasis. Studies indicate that approximately 30% of patients with diabetes progress to either proliferative retinopathy or macular oedema over a 14-year period.2 New vessels arise most frequently on the optic disc or along the course of the major retinal veins. Unfortunately, wherever the vessels grow on the surface of the retina, they become adherent to the vitreous. When the vitre-ous contracts, it cannot easily separate from the retina and the vitreous pulls on the fragile new vessels, causing rupture of their walls and vitreous haemorrhage. Subsequently tractional retinal detachment may also ensue. A fuller description of the clinical grading of diabetic retinopathy is shown in Table 3.1. Before the availability of laser photocoagulation, 50% of eyes with fully developed proliferative retinopathy progressed to marked reduc-tion of vision and often complete blindness.3

In the past, considerable controversy existed regarding the role of accurate control of diabetes in the prevention of retinopathy, as well as nephropathy and other vascular complications. The recent United Kingdom Prospective Diabetic Study has confi rmed that good control of blood sugar levels is important in the prevention of both microvascular and macrovascular complications.4 This study also highlighted the importance of attending to the other ‘bad companions’ of diabetes – hypertension, hypercholesterolae-mia and smoking. It is essential that all those involved in manag-ing patients with diabetes have a thorough understanding of its complications and that they are willing to devote considerable time to education of their patients.

Practical advice

Patient education is absolutely essential, as it is the patient who must understand and manage their disease from day to day and from hour to hour. In some diabetic units, a diabetic education centre and a diabetic liaison nurse are available to improve diabetic knowledge.

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Table 3.1 Grading of Diabetic Retinopathy

Grade of Clinical signs Features on

retinopathy angiography

Background Venous dilatation Leakage from (can be preclinical); microaneurysms; microaneurysms; dot masking due to haemorrhages; blot haemorrhages and haemorrhages; hard exudates exudates

Maculopathy Exudative Microaneurysms; hard Diffuse or focal leakage exudates – diffuse or from microaneurysms; circinate little, if any, capillary fall-out

Oedematous Retinal thickening – focal or Predominantly diffuse; microaneurysms; intraretinal leakage ± dot and blot haemorrhages ischaemia

Ischaemic Microaneurysms; large blot Widespread areas of and blotch haemorrhages ± capillary fall-out often retinal thickening involving the perifoveal arcade

Pre-proliferative All features of background Widespread inner retinopathy plus cotton- retinal ischaemia; wool spots; widespread masking from large intraretinal haemorrhages; haemorrhages; IRMAs venous dilatation, beading and venous loops; intraretinal microvascular abnormalities (IRMAs)

Proliferative New vessels on the disc or Widespread inner elsewhere; fi brous tissue; retinal ischaemia; pre-retinal and vitreous profuse early leakage haemorrhage; ‘raspberry’ from new vessels or abortive neovascular outgrowth

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3.1.2 Prevalence of diabetic retinopathy

The prevalence of diabetic retinopathy increases with duration of diabetes. In type 1 (juvenile) diabetes, retinopathy is virtually never present in the fi rst 5 years. However, 27% of those who have had diabetes for 5–10 years and 71% of those who have had dia-betes for 10 years or longer will have diabetic retinopathy. After 30 years the incidence rises to 90%, with 30% of these patients having proliferative diabetic retinopathy (PDR).5 Times of added risk are around puberty and during pregnancy. In adult onset diabetes, maculopathy is more common than proliferative reti-nopathy but may in some cases be associated with neovascularisa-tion. Often in patients with type 2 diabetes, maculopathy can be the presenting feature of the disease. Adult-onset diabetes can remain undiagnosed for many years, with severe damage to the retinal capillaries resulting in subsequent irreversible visual loss.

Practical advice

Visual acuity may appear good even in the presence of PDR or extensively treated non-proliferative retinopathy.

3.1.3 Laser photocoagulation and surgery for diabetic retinopathy

Laser photocoagulation of the diabetic retina utilises an argon or krypton laser to coagulate ischaemic retina, rendering the isch-aemic retina non-viable and thereby removing the stimulus for neovascularisation. Recent randomised controlled studies have shown that laser photocoagulation is effective in preserving vision and slowing the rate of visual decline in diabetic patients with pre-retinal and papillary neovascularisation and early maculopa-thy.5–7 Advanced retinal neovascularisation and macular oedema respond less favourably to photocoagulation; thus, it is imperative to detect disease in its early stages by meticulous screening and careful observation of diabetic patients. Persistent dense vitreous haemorrhage, fi brovascular membranes and traction detachments, which threaten macular function, may be treated by vitrectomy. This technique may dramatically improve visual function by irri-gating blood from the vitreous cavity using an intraocular infu-sion and suction system, fi tted with a cutting head. Fibrovascular

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membranes may also be carefully dissected from the retinal surface.7

3.1.4 The management of diabetic retinopathy

The management of diabetic retinopathy has been the subject of many excellent randomised controlled trials, with the result that many management questions have been answered conclusively. Some questions that are of paramount importance to both the patient and the surgeon are discussed below.

Q.1 Does laser photocoagulation have any impact on the progression of retinopathy?

Yes. Laser photocoagulation has been shown to reduce blindness in diabetic retinopathy by 50%.

Q.2 When should laser be applied in proliferative retinopathy?

The Early Treatment Diabetic Retinopathy Study (ETDRS) has shown that panretinal laser photocoagulation (PRP) (Fig. 3.1 [Plates 5 & 6]) should be applied when ‘high risk’ criteria are present. High-risk criteria are as follows and indicate the need for prompt and aggressive PRP:

• NVD (new vessels on the disc) covering more than one-quarter to one-third of the disc area

• NVD covering less than one-quarter to one-third of the disc area in the presence of pre-retinal or vitreous haemorrhage

• NVE (new vessels elsewhere) with pre-retinal or vitreous haemorrhage.

Q.3 Is laser treatment equally helpful for all types of maculopathy?

No. Unfortunately laser therapy is not helpful in all types of maculopathy. Exudative maculopathy responds best, in particular for patients who have circinate patterns of hard exudates. Oedematous maculopathy responds, at best, with stabilisation of vision in 30% of patients. No treatment has

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been found to be of help in ischaemic maculopathy; in fact, laser photocoagulation can sometimes exacerbate the situation. The outcome for patients with mixed maculopathies depends on the degree of each of the above components. Patients are often disappointed if they are told that they are unsuitable for laser treatment, or that it would not be of benefi t. These patients usually have an ischaemic type of maculopathy.

Q.4 Should laser treatment be applied in pre-proliferative retinopathy?

No, although it would appear sensible to pre-empt complications. The reason that laser treatment is not automatically indicated in all patients who develop to pre-proliferative retinopathy is that only 50% will progress to full-blown PDR. In addition, PRP is not without side-effects.

Q.5 Are there any side-effects to laser photocoagulation?

Yes. The potential side-effects of laser treatment, whether permanent or transient, are many (Table 3.2). In practice, the most common side-effects of PRP are night blindness and loss of the peripheral fi eld. These side-effects are, however, well tolerated by patients and are often accepted as a necessary pay-off against the preservation of what can often be excellent central acuity. Patients who have had successful PRP often maintain 6/6 [LogMAR 0.0] vision 20–30 years later. What is often most annoying for patients is the photophobia associated with scatter PRP. This is thought to be due to internal scattering and refl ection of light from the laser scars.

In providing low vision support for those with visual impairment resulting from diabetes, the key is versatility. As aspects of the underlying condition change (lens hydration, macular oedema, retinopathy), so do refractive status and visual function. Specta-cles must be kept up to date and a range of low vision aids, some of which are designed to enhance contrast, provided. Advice on a wide range of visual rehabilitation strategies and various forms of

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A

BFigure 3.1 A & B (Plates 5 & 6) Treated diabetic retinopathy in a 24-year-old woman. The patient has been treated with panretinal photocoagulation for proliferative retinopathy (scars in the peripheral retina of the left eye – B) and with bilateral grid laser for maculopathy (subtle scars in the macular areas – A & B).

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assistive technology (both low and high tech) should be provided.

3.1.5 The St Vincent’s Declaration

In 1989, the World Health Organization and the International Dia-betes Federation for Europe drew up a joint initiative on diabetes care and research into diabetes mellitus.8 Central to the initiative was the inclusion of 5-year targets for improvement in all diabetic complications, including the reduction of diabetic blindness by one-third. Following the St Vincent’s Declaration, a uniform pro-

CFigure 3.1 C (Plates 5 & 6) Corresponding ‘binocular Estermann’ fi elds show both peripheral and central fi eld loss secondary to laser photocoagulation. This patient would not be eligible to hold a driving licence. Black rectangles indicate loss of function.

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tocol was developed in a joint venture by 21 European countries for the screening of diabetic retinopathy. This protocol includes guidelines for examination and a data collection sheet.9 To date, little progress appears to have been made in addressing these aims in a practical way.

3.2 Pathological myopia


The prevalence of myopia varies between 11% and 36% of the general population, with 30% of the myopic population and 1–4% of the general population exhibiting high myopia, which is defi ned as more than 6 dioptres of myopia. Pathological myopia can be considered to be greater that 15 dioptres of refractive correction. Myopia is thought to be transmitted in a dominant fashion. Females seem to be at greater risk of high myopia and degenerative changes; the main risk threatening central vision is macular disease with lacquer cracks and haemorrhages associated with choroidal neo-vascularisation. The following fundal changes are found in those with pathological myopia:

Table 3.2 Side-Effects of Argon Laser Panretinal Photocoagulation

Transient side-effects Permanent side-effects

Blurring of vision Loss of visual acuity

Choroidal detachment Accommodative defects (due to damage to long ciliary nerves and resulting recession of the near point)

Macular oedema – can Dimness of vision (dose related if >2000persist for weeks but usually burns at one sitting)settles. More common in type II diabetes after PRP

Headache Nyctalopia

Loss of colour vision

Photophobia

Loss of peripheral fi eld

Inadvertent foveal burn

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66

• Chorioretinal atrophy• Choroidal neovascular membranes (CNVMs) are thought to

occur in 5–10% of myopes with more than 5 dioptres of myopia

• Diffi culty in viewing the foveal limits• Haemorrhage associated with a lacquer crack (can occur in

the absence of a CNVM)• Lacquer cracks – linear or stellate• Myopic conus• Myopic crescents are usually temporal to the disc• Thinned retinal pigment epithelium and choroid.

Practical advice

Owing to the large degree of direct ophthalmoscope magnifi cation when examining the myope, full examination of the fundus is virtually impossible unless indirect ophthalmoscopy or a fundus lens is used.

The appearance of a CNVM in myopia varies with the age of the lesion. It begins as a dark brown spot at the centre of the fovea, which is representative of a collection of blood. As the lesion degenerates, it evolves into a yellowish-grey rounded or pigmented lesion, known as a Forster–Fuchs’ spot. The visual prognosis in CNVM in myopia remains controversial, with results on prognosis for patients with myopic CNVM varying from study to study. Hampton et al10 reported that 60% of patients do not improve beyond logMAR 1.0 (6/60) at best, and that 43% lose at least two lines of vision. It is generally agreed that a rapid decrease in vision occurs at the onset of the disease, thought to be due to a short neovascular growth phase. In general, CNVMs in myopia remain smaller and more confi ned than those in age-related macular degeneration (AMD), and many heal with resultant reasonable vision unless the CNVM is subfoveal. Pathological myopia is asso-ciated with a 34% rate of of legal blindness in the long term.

Laser photocoagulation has been used to treat these lesions. A randomised controlled trial of the use of krypton red laser in extrafoveal CNVMs in myopes under the age of 55 years who have had a CNVM 100–1000 μm from the fovea has been reported.11 From the practical viewpoint, the operators had great diffi culty in

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localising the fovea during treatment. The results showed that 40% in the treated group versus 13% in the untreated group had an increase of two lines of visual acuity. Some 40% of the treated and 77% of the untreated group had a drop of two lines, indicating that treatment is probably benefi cial. Following early experience of treating CNVMs it was noted that the laser scar often enlarged after treatment. This is known as ‘run-off’. However, studies have shown that treatment ‘run-off’ does not necessarily decrease vision, even if it extends into the foveal area. Krypton red was chosen for this study because of its better absorption by choroidal melanocytes; it is therefore thought to be useful in the lightly pigmented fundus of the myope. Myopes are, of course, predis-posed to other ophthalmic conditions such as retinal detachments, cataract and chronic open angle glaucoma.

It must also be remembered that the magnitude of myopia is prone to increase, and high myopes should be re-refracted regu-larly and provided with an optimal correction in either spectacle or contact lens form. Highly myopic, visually impaired, spectacle wearers benefi t from the easily accessible magnifi cation of near objects achieved by removing their correction. This is not such a viable option for the contact lens wearer.

3.3 Acute optic neuritis

The incidence of acute optic neuritis varies signifi cantly between geographical areas. Studies estimate the prevalence of optic neu-ritis to be 46 per 100 000 in the USA, 93 per 100 000 in England and Wales, and 0.77 per 100 000 in Hong Kong.12 Patients with optic neuritis present with sudden blurring of vision, which is usually unilateral and of gradual onset, but progressive. The visual loss is characteristically associated with pain on ocular movement. Clinical examination shows deceased visual acuity, an afferent pupillary defect, loss of appreciation of the colour red and optic disc swelling, if the nerve head is involved. Most cases are due to retrobulbar pathology, so that the optic disc appears normal.

Practical advice

There are only two causes of pain on ocular movement, in the presence of normal orbit and globe: infl uenza and optic neuritis.

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The management of optic neuritis has for many years been con-troversial. The recent report on the 10-year follow-up of the Optic Neuritis Treatment Trial (ONTT) has helped to give guidance in this area. The following is a synopsis from the 2004 report of the ONTT:13

The criteria for entry into the ONTT included a diagnosis of acute unilateral optic neuritis with visual symptoms for 8 days or less, age between 18 and 46 years, no previous history of optic neuritis or ophthalmoscopic signs of optic atrophy in the affected eye, and no evidence of a systemic disease other than MS that might be associated with the optic neuritis. Patients who experienced prior episodes of optic neuritis in the other (fellow) eye or prior demyelinative attacks of MS were eligible only if corticosteroids had not been prescribed. This minimised the number of patients enrolled who had a prior diagnosis of MS, and those diagnosed as having MS at the time of enrolment had minimal or no neurologic disability. At study entry, patients were randomly assigned to receive a short course of oral prednisilone, oral placebo, or intravenous methylprednisolone sodium succinate followed by oral prednisone. Patients were examined at eight follow-up visits within the fi rst year and then at yearly intervals until 1997. From 2001 to 2002, the consenting patients were recalled for a further examination.

The 10-year review of the ONTT showed the following:

Examinations were completed on 319 patients. In most patients, visual function test results in the eyes that experienced optic neuritis at study entry (‘affected eyes’) were normal or only slightly abnormal after 9.9 to 13.7 years. Visual acuity in the affected eyes was > or = 20/20 in 74%, 20/25 to 20/40 in 18%, <20/40 to 20/200 in 5%, and <20/200 in 3%. On average, visual function was worse in patients with multiple sclerosis (MS) than in those without MS. Recurrent optic neuritis in either eye occurred in 35% of patients. Such attacks were more frequent in patients with MS (P<.001). The National Eye Institute Visual Function Questionnaire scores were lower when visual acuity was abnormal and when MS was present. CONCLUSIONS: Most patients retained good to excellent vision more than 10 years after an attack of optic neuritis . . . Although a signifi cant proportion of patients presenting with isolated optic neuritis go on to develop MS in the future, the exact number varies between studies and length of

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69

follow up. Recurrences are, however, more frequent in patients with MS.13

Practical advice

Red desatuaration is a very easy but important test to perform in a patient suspected of having optic neuritis. The progression or regression of red desaturation is also a sensitive indicator of the clinical progression or regression of the episode.

3.4 Posterior uveitis

Posterior uveitis, an infl ammatory process of the uveal tract (iris, cilary body and choroid), is a rare condition with an incidence of 15 per 100 000 and a prevalence of 40 per 100 000 population. Although rare, posterior uveitis accounts for 10% of blind registra-tion in developed countries. The successful management of poste-rior uveitis is dependent upon an accurate diagnosis of ‘infective’ or ‘non-infective’ causes. Treatment of infective retinopathies such as toxoplasmosis is primarily with the appropriate anti-infective agent, whereas management of non-infectious posterior uveitis is with immunosuppressive agents. More recently the availability of new non-steroid-based immunosuppressants has improved the visual prognosis and quality of life for these patients, who often require medication for many years. Three of the more common causes of visual loss and visual disability are discussed below.

Toxoplasma retinochoroiditis

Toxoplasma gondii is an obligate intracellular parasite whose natural host is the cat.14 The disease is transmitted to humans through cat faeces. In the UK, most of those affected are immunocompetent and present with reactivation of congenital toxoplasma scars that have been present since birth and were acquired through maternal infection in pregnancy. Interestingly these lesions seem to reacti-vate only during early adulthood; reactivation before the age of 18 years and after the age of 45 years is very rare. Treatment is with a combination of either clindamycin and oral corticosteroids, or pyrimethamine, sulfonamides, folinic acid and steroids. As the condition is self-limiting, not all patients with active lesions require treatment. Treatment is indicated only if the lesion is threatening

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70

the optic disc, the macula or a major vessel. If the lesion is close to the fovea, the pyrimethamine regimen detailed above is recom-mended, because fi nal scar size has been shown to be reduced with this treatment.

Until quite recently, the diagnosis of a primary acquired as opposed to a secondary or congenital toxoplasmosis invoked ques-tions about the immune status of the individual. However, more recently apparently healthy people have presented with primary or acquired toxoplasmosis. The acquired toxoplasma lesion is clin-ically different from the reactivated congenital lesion. The cardinal features of a primary toxoplasma lesion are: a white, smooth, ele-vated retinochoroidal lesion usually found at the posterior pole; the relative absence of the vitritis usually associated with a reac-tivated lesion; and no evidence of chorioretinal scarring either at the edge of the lesion or elsewhere in the fundi. In contrast, in secondary toxoplasmosis the fundal lesion will show evidence of an old pigmented scar with an active white edge or fresh lesion. This is usually accompanied by signifi cant vitritis. The clinical management is the same for both lesions, with due consideration for the patient’s immunocompetence status.

Punctate inner choroidopathy

Punctate inner choroidopathy is a bilateral infl ammatory condition that affects young adults.15 The clinical features of the syndrome include moderate myopia, blurring of vision associated with pho-topsia and scotoma. The condition usually presents in young women. The clinical fi ndings are multiple yellow–white lesions of the inner choroid and retina, largely confi ned to the posterior pole. Usually the eyes are quiet with no signs of intraocular infl amma-tion. These lesions heal and leave atrophic scars that are prone to neovascularisation, which occurs in 40% of eyes, and are usually responsible for loss of vision. The underlying aetiology remains unknown, although fundal changes found in this condition are similar to those found in the presumed ocular histoplasmosis syn-drome (POHS), and therefore a viral aetiology has been assumed.

Practical advice

Patients with punctate inner choroidopathy usually present only when the complication of choroidal neovascularisation occurs in a central scar, causing blurring and distortion of vision.

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71

The natural history of these lesions is more favourable than in AMD. Laser photocoagulation for extrafoveal lesions, and more recently photodynamic therapy (PDT) for juxtafoveal or subfoveal lesions, can further aid resolution. The role of steroids remains contentious, but they may have a place in dampening the infl am-matory response in the stage of neovascularisation. The prognosis for vision is relatively good, with 50% of eyes retaining a visual acuity of 6/18 [LogMAR 0.5] or better. The clinical distinguishing features of the more common infl ammatory retinopathies are shown in Table 3.3.

Serpiginous chorioretinitis

This is a bilateral progressive infl ammatory disease of the inner choroid, retina and retinal pigment epithelium.16 The lesions, which begin in the peripapillary area and spread centrifugally in a jig-saw-like pattern, are well circumscribed gray–white lesions. The patient is typically a healthy young or middle-aged individ-ual. The signs are accompanied by infl ammatory cells in approxi-mately one-third of cases. Clinically, serpiginous chorioretinitis can easily be confused with acute multifocal placoid pigment epitheliopathy (AMPPE). The lesions can initially be similar in appearance; however, serpiginous chorioretinitis is recurrent whereas AMPPE is not. Serpiginous chorioretinitis is a chronic, relapsing condition with progressive loss of the visual fi eld and sometimes central visual acuity. Some 25% of these patients develop choroidal neovascularisation.

3.5 Cytomegalovirus retinitis

The incidence of cytomegalovirus (CMV) retinitis has risen dra-matically over the past 10 years. Although approximately 80% of the normal population have been infected with CMV systemically, in those who have normal immunity (i.e. are immunocompentent) CMV causes no problem. CMV retinitis is an opportunistic infec-tion affecting those who have compromised immune systems due to either immunosuppressant drug therapy or infection with human immunodefi ciency virus (HIV).17 The retinitis presents with retinal necrosis and intraretinal haemorrhage. The appear-ance has been graphically described as ‘tomato ketchup and mayonnaise’ retinopathy. Those infected with HIV gradually

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72

Ta

ble

3.3

Fun

dal C

hang

es in

the

Infl

am

mat

ory

Ret

inop

athi

es

A

nte

rio

r V

itre

ou

s C

ho

rio

reti

nal

Ap

pe

ara

nce o

f C

ho

roid

al

u

ve

itis

ce

lls/v

itri

tis

scars

acu

te l

esi

on

s n

eo

vasc

ula

r

m

em

bra

ne

(C

NV

M)

Punc

tate

inne

r N

one

Non

e Pu

ncta

te le

sion

s U

sual

ly C

NV

M

Yes

chor

oido

path

y

th

roug

hout

fun

dus

(PIC

)

Acq

uire

d Fe

w c

ells

Q

uiet

vit

reou

s –

No

prev

ious

sca

rs

Whi

te f

ocal

ele

vate

d N

oto

xopl

asm

osis

few

cel

ls o

nly

re

tina

l les

ion

Con

geni

tal

Bri

sk ir

itis

V

itri

tis

++

+

Usu

ally

bila

tera

l Pa

le a

ctiv

e le

sion

at

Yes

toxo

plas

mos

is

pigm

ente

d bo

rder

of

old

scar

ch

orio

reti

nal s

cars

Serp

igin

ous

Qui

et

Post

erio

r vi

treo

us

Jig-s

aw p

atte

rn f

rom

R

etin

al p

igm

ent

Ye

sch

oroi

diti

s

cells

30%

op

tic

disc

ep

ithe

lium

mot

tlin

g

an

d pi

gmen

tati

on

w

ith

acti

ve e

dge

whi

te

for

mon

ths

Acu

te m

ulti

foca

l Q

uiet

V

itre

ous

cells

50%

Ir

regu

lar

clum

ps o

f G

ray–

whi

te le

sion

s N

opl

acoi

d pi

gmen

t

pi

gmen

tep

ithe

liopa

thy

(AM

PPE)

Ch003-H1815.indd 72 9/15/2006 12:08:01 PM


73

lose the function of their T cells (required to fi ght infections). CMV retinitis rarely occurs until the patient is severely immunocompromised.

Practical advice

Studies have shown that, if an immunocompromised patient with a T4 count <50 cells per cubic millimetre of blood complains of fl oaters, the probability of CMV retinitis being present is approximately 80%.

CMV retinitis can initially affect either the posterior pole or the peripheral retina. Either type of lesion leads rapidly to blindness if untreated. CMV retinitis is reported to progress at a rate of one disc area every 6 weeks. Those with peripheral retinal lesions are more at risk of retinal detachment, which occurs in 20% of these patients.

The treatment of CMV retinitis has improved, as has treatment of the underlying illness. Several years ago the survival of a patient once diagnosed with CMV retinitis could be measured in terms of 4–5 months, whereas today survival can be indefi nite. Interest-ingly, since the advent of highly active antiretroviral therapy (HAART) for those infected with HIV, the incidence of CMV reti-nitis has fallen dramatically.18 Treatment for CMV retinitis, when it occurs, can be given intravenously, by repeated intravitreal injec-tions or by a long-acting intravitreal delivery ganciclovir implant (Retisert).19 Each method of treatment has its own advantages and disadvantages. In the era before HAART was readily available, some patients proceeded to be visually impaired, despite aggres-sive therapy. These patients often benefi t from the use of low vision aids. Despite the multiple problems that these patients have, one of the overriding fears is that they will go blind before they die. Maintenance of useful visual acuity and independence is therefore of paramount importance.

3.6 Trauma

Trauma is an unusual cause of bilateral blindness, although non-belted car occupants in road traffi c accidents, electrocutions, chemical injuries and self-infl icted injuries can cause bilateral and

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74

signifi cant visual impairment. Reductions in visual impairment resulting from trauma are achieved primarily through the dis-semination of health and safety information to those undertaking potentially hazardous activity when in employment and at home (DIY). All of those involved in the provision of ‘eye care’ must play their part in this process. Cortical blindness from head injuries can also cause bilateral visual loss, although the nature of the loss can be complex, involving both visual and perceptual compo-nents. The rate of bilateral perforating eye injuries sustained through road traffi c accidents has been reduced to almost negli-gible proportions since the advent of seat belt enforcement.

3.7 Low vision aids

1. As they get older, management of those with a stable childhood condition involves:a. The provision of low vision aids for new tasks

(employment), CCTVs, computer systems with speech recognition or large print computer access programs, and distance monoculars as their world becomes bigger and motility needs increase.

b. The consideration and discussion of registration as adult ‘state benefi ts’ often kick-in for those on the Blind Register.

c. Discussion of changes in accommodation power in those with nystagmus, albinism, etc. These patients may no longer cope purely by accommodating but may now need near vision aids or suffer from headaches, eyestrain and limited concentration.

d. Remembering that those who suffer from heritable conditions may develop progressive myopia, but might not need it corrected until 18 or 20 years of age.

2. Those with adult-onset blindness or visual impairment need follow-up advice on lighting and good posture. In particular, diabetics who have progressive and variable visual loss need regular follow-up and versatile low vision aids with good contrast enhancement.

3. Adults who need low vision aids for home use may also require more discrete portable folding hand magnifi ers, miniature monoculars or spectacle magnifi ers as portable low vision aids.

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75

3.8 Summary

The young adult who presents with visual impairment is often the most diffi cult to manage. Patients in this age group are often the breadwinner, and visual impairment results in loss or change of employment, driving, and often in profound changes in interper-sonal relationships and roles. It is important to remember that, for the younger adult, honest and practical advice is imperative in terms of prognosis and future career choices. Those who have had problems since childhood are often coping well and can proceed with appropriate careers; it is the newly diagnosed who require much support and also detailed genetic counselling regarding transmission of the disease to future offspring.

References

1. Frank RN. On the pathogenesis of diabetic retinopathy. Ophthalmology 1984; 91:626–634.

2. Klein R, Klein BE, Moss SE, Cruickshanks KJ. The Wisconsin Epidemiologic Study of Diabetic Retinopathy: XVII. The 14-year incidence and progression of diabetic retinopathy and associated risk factors in type 1 diabetes. Ophthalmology 1998; 105:1801–1815.

3. Kohner EM. The evolution and natural history of diabetic retinopathy. International Ophthalmology Clinics 1978; 18:1.

4. Nasr CE, Hoogwerf BJ, Faiman C, Reddy SS. United Kingdom Prospective Diabetes Study (UKPDS). Effects of glucose and blood pressure control on complications of type 2 diabetes mellitus. Cleveland Clinic Journal of Medicine 1999; 66:247–253.

5. Diabetic Retinopathy Study Research Group. Photocoagulation treatment of proliferative diabetic retinopathy: the second report of diabetic retinopathy study fi ndings. Ophthalmology 1978; 85:82–106.

6. Early Treatment Diabetic Retinopathy Study Research Group. Photocoagulation for diabetic macular edema: Early Treatment Diabetic Retinopathy Study Report No. 1. Archives of Ophthalmology 1985; 103:1796–1806.

7. Diabetic Retinopathy Vitrectomy Study Research Group. Early vitrectomy for severe vitreous haemorrhage in diabetic retinopathy: two year results of a randomized clinical trial. Diabetic Retinopathy Vitrectomy Study Report 2. Archives of Ophthalmology 1985; 103:1644–1652.

8. International Diabetes Federation. Diabetes Care and Research in Europe: The St Vincent Declaration 1989. Online. Available:

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http://www.idf.org/webdata/docs/SVD%20and%20Istanbul%20 Commitment.pdf [21 March 2006].

9. Kohner EM, Porta M. Protocols for screening and treatment of diabetic retinopathy in Europe. European Journal of Ophthalmology 1991; 1:46–54.

10. Hampton GR, Kohen D, Bird AC. Visual prognosis of disciform degeneration in myopia. Ophthalmology 1983; 90:923–926.

11. Pece A, Brancato R, Avanza P, Camesasca F, Galli L. Laser photocoagulation of choroidal neovascularization in pathologic myopia: long-term results. International Ophthalmology 1994–95; 18:339–344.

12. Chan CK, Lam DS. Optic neuritis treatment trial: 10-year follow-up results. American Journal of Ophthalmology 2004; 138:695; author reply 695.

13. Beck RW, Gal RL, Bhatti MT et al. Visual function more than 10 years after optic neuritis: experience of the optic neuritis treatment trial. American Journal of Ophthalmology 2004; 137:77–83.

14. Hogan MJ. Ocular toxoplasmosis; clinical and laboratory diagnosis: evaluation of immunologic tests; treatment. Archives of Ophthalmology 1956; 55:333.

15. Watzke RC, Packer AJ, Folk JC et al. Punctate inner choroidopathy. American Journal of Ophthalmology 1984; 98:572–584.

16. Weiss H, Annesley WH Jr, Shields JA et al. The clinical course of serpiginous choroiditis. American Journal of Ophthalmology 1979; 87:133–142.

17. Kramer M, Lynn W, Lightman S. HIV/AIDS and the eye. Hospital Medicine 2003; 64:421–424.

18. Roels P. Ocular manifestations of AIDS: new considerations for patients using highly active anti-retroviral therapy (HAART). Optometry 2004; 75:624–628.

19. Driot JY, Novack GD, Rittenhouse KD, Milazzo C, Pearson PA. Ocular pharmacokinetics of fl uocinolone acetonide after Retisert intravitreal implantation in rabbits over a 1-year period. Journal of Ocular Pharmacology and Therapeutics 2004; 20:269–275.

Ch003-H1815.indd 76 9/15/2006 12:08:01 PM

Causes of loss of vision in the elderly are numerous and varied. Some causes, such as cataract, are amenable to successful treat-ment, others unfortunately are not. The most common causes of visual loss in the elderly are described in this chapter, with empha-sis on important diagnostic features of these conditions. Disease processes aside, increasing age brings certain well documented changes to the normal healthy ageing eye, which should not be considered synonymous with visual loss (Table 4.1).

4.1 History and visual assessment in the elderly

Elderly patients often give a very helpful and detailed history, with the result that a presumptive diagnosis can be made on history taking alone and then verifi ed by examination. Some elderly patients are slower at performing assessment tasks and should be encouraged. It should also be noted that the elderly, especially those with age-related macular degeneration (AMD), can have trouble mastering the art of the ‘pinhole’ and may benefi t from refraction, irrespective of the fact that a pinhole fails to improve on the acuity recorded with habitual correction in place. Although few eyes that have survived 65 or more years of life are free from at least some slight sign of deterioration, degeneration, or past or present disease, 14.5% of patients aged 70–74 years have corrected vision of less than 6/7.5 [LogMAR 0.1], yet have no

77

CHAPTER

Visual impairment in the elderlyGiuliana Silvestri

444

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78

clinically reported degenerative or disease conditions.1 The eyes are found to be clinically normal. When examining eyes in the elderly it is important to understand which changes may be regarded as a physiological part of ageing. The known changes with ageing in the various structures of the eye are listed in Table 4.1.

4.2 Age-related macular degeneration

4.2.1 Aetiology

AMD, fi rst described in 1885, is a progressive disabling bilateral condition that is responsible for 30–49% of new blind registrations per year in the UK.2,3 Although the condition is common, until recently the underlying aetiology remained an enigma. Numerous potential risk factors such as age, sex, race, height, social status, hypertension, cardiovascular and cerebrovascular disease, refrac-tive error, personal attributes such as eye colour, skin characteris-tics, light exposure and nutritional factors have been implicated in the causation of AMD. The only defi nitive contributory evi-dence that has been found is for cigarette smoking, hypertension and hereditary factors.4–7 It appears likely that AMD is a multifac-torial disease triggered by environmental infl uences in those who are genetically predisposed. The genetic factors implicated are described in Section 4.2.4. The prevalence of AMD ranges from 0.2% in those aged 50–54 years, to 1.5% in those aged 70–74 years, to 16.4% in those aged 80 years or more.8

4.2.2 Clinical features

Clinically, AMD is a heterogeneous disease and is classifi ed into two subgroups: a ‘dry’ or ‘atrophic’ form (80%) and an exudative or ‘wet’ form (20%).3 Exudative AMD, although much less common, is responsible for the majority of cases of severe loss of central vision. Symptoms of AMD are listed in Table 4.2. Drusen are the hallmark of AMD and, on ophthalmoscopic examination, appear as small, bright, sharply defi ned, circular points lying beneath the retinal vessels, confi ned mostly to the posterior pole. Drusen can vary in size and shape, and occasionally present a crystalline appearance resulting from calcifi cation. Histologically, hard drusen have been identifi ed at the macula in 83% of normal adult

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4Visual impairment in the elderly 44

79

Table 4.1 Non-pathological Changes in the Eye with Age

Cornea Corneal sensitivity to touch is decreased

Increase in ‘against the rule’ astigmatism

Anterior Anterior chamber depth decreases with agechamber

Iris Senile miosis

Pigment desquamation into the anterior chamber

Lens Increase in axial thickness by about 28%

Increase in the amount of yellow pigment leading to decreased sensitivity at the violet end of the spectrum

Decrease in accommodation, possibly due to a decrease in capsular elastic force

Little evidence to support atrophy or sclerosis of the ciliary muscle

Vitreous Chromatic aberration decreases with age

Index of refraction of the vitreous increases

Liquefaction and syneresis occur

Retina Visual acuity decreases as age increases. In most cases, pathology is found but in about 10% of patients aged 75–85 years vision is less than 6/7.5 [LogMAR 0.1] and they are entirely free from ocular disease

Visual fi eld size decreases

Loss of ability to discriminate hues, especially at the violet end of the spectrum. Mesopia and scotopia occur at lower levels of ambient illumination

Absolute level of dark adaptation achieved is lower

Delayed recovery to glare

Loss of contract sensitivity at low frequencies

Decrease in retinal illuminance

Decline in acuity with target velocity with increasing age

Variability in visual performance increases with age

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80

eyes. Most drusen cause little disturbance and often remain unde-tected.9 Drusen have been noted to occur in the fundi of persons as young as 30 years of age, and have been noted to lie within 1500 μm from the fovea, even at this age.10 With time, drusen tend to enlarge and undergo atrophy.

‘Dry’ AMD

As the changes in ‘dry’ AMD progress, the photoreceptors, retinal pigment epithelium and, in some cases, the choriocapillaris are lost in the atrophic areas. The advanced stage of ‘dry’ AMD is known as geographic atrophy. Geographic atrophy often starts in the perifoveal region and, over a period of years, the atrophy tends to expand in a horseshoe-like fashion around the central fovea, usually closing on the temporal or nasal side and then fi nally invading the foveola.11 As AMD progresses, it has been noted that hard drusen undergo softening to form soft drusen. Patients with soft drusen are more likely to progress to ‘choroidal neovasculari-sation’. The pathway for the clinical management of patients with drusen is shown in Figure 4.1. Although severe visual loss is pos-sible in ‘dry’ AMD, severe loss of central vision (i.e. LogMAR 1.0 – <6/60) does not usually occur until 80% of the fovea has been damaged. From a practical viewpoint, this leads to an inability to recognise faces and to near vision problems, which need to be managed using large print or simple low vision aids. Patients with geographic atrophy, however, are often more symptomatic than their signs might suggest.

Table 4.2 Symptoms of AMD

‘Dry’ AMD ‘Wet’ AMD

Reduced near vision and reading speed Acute distortion of vision (metamorphopsia)

Central or paracentral scotoma Sudden loss of central vision

‘Jumbling’ of words and letters Red discoloration of vision

Formed visual hallucinations Formed visual hallucinations

Ocular pain due to massive subretinal haemorrhage

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81

‘Wet’ AMD

Choroidal neovascularisation is the hallmark of exudative or ‘wet’ AMD. The disciform response, which is so often seen in the end-stage of ‘wet’ AMD, is due to the infi ltration of Bruch’s membrane and the subretinal space by new choroidal vessels. Serous exuda-tion, haemorrhage and fi brosis then ensue, leading to subretinal fi brosis and scarring. Occasionally massive subretinal, intraretinal

Figure 4.1 Management pathways for the patient presenting with drusen. All patients with bilateral loss should be offered low vision assessment/training and visual rehabilitation support. CNVM, choroidal neovascular membrane; FA, fl uorescein angiography; GA, geographic atrophy; PED, pigment epithelial detachment; RPE, retinal pigment epithelium.

DRUSEN

Hard

AsymptomaticNormal visual

acuity

No actionSupply Amsler

chart

Symptomaticwith reducedvisual acuity

CNVM

FA if CNVMpresent

Laser Radiotherapynot proven

SurgeryAnti VEGFcompounds

No treatmentOccult

CNVM/PED

GA

GA andhaemorrhage

PED

Soft

Argon/krypton Photodynamictherapy

FA

Non-vascularised

Laser(to flatten)

Laserto CNVM

Flattens or risk of RPE rip

Nolaser

Notreatment

Vascularised

Ch004-H1815.indd 81 9/15/2006 12:08:55 PM


82

and intravitreal haemorrhage can occur from such a lesion. Retinal pigment epithelial detachments associated with choroidal neovas-cularisation are the presenting clinical features in 10% of patients with AMD. Patients with the exudative form of the disease often complain of the sudden onset of metamorphopsia (distortion of vision), decreased near vision acuity, micropsia (objects appear smaller) or scotoma. The speed of onset of visual compromise can be devastating to the patient, both psychologically and practically. The disease, although bilateral, is often asymmetrical, and visual acuity can remain good in one eye for a number of years. Patients are often unaware that the fi rst eye has been affected until quite late in the process, by which time any possible therapeutic window has passed. Involvement of the second eye, by choroidal neovas-cularisation, occurs at a rate of 13% per year.

Patients with advanced AMD can experience visual hallucina-tions. This is known as the Charles Bonnet syndrome.12 However, the patient, for fear of being labelled ‘mad’, rarely reports these hallucinations. Recently, in a study of the patients attending our retinal clinic with AMD, the incidence of formed hallucinations was found to be 12%. The hallucinations are usually complex formed images, which are recurrent. The cause of these hallucina-tions is unknown, but chronic deprivation of the sensorium from visual input is thought to play a part. If necessary, hallucinations, which can be very disconcerting, can be controlled using anti-psychotic medications. However, once a patient with AMD and visual hallucinations is reassured that these are part of the normal process of advanced bilateral visual loss in AMD, they begin to view their visual aura with interest and acceptance (see Ch. 18, Section 18.5).

Practical advice

Once patients with visual hallucinations have been reassured that this is related to their eye condition, treatment is often unnecessary and the patients proceed to view the images with interest.

4.2.3 The role of fl uorescein and indocyanine green angiography in AMD

The experienced clinical observer can often be fairly confi dent of the distinction on clinical examination between ‘wet’ and ‘dry’

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83

AMD. However, if there is doubt as to whether a neovascular component is present or treatable, then urgent fl uorescein angio-graphy is indicated (Fig. 4.2). Angiography is also indicated to defi ne the type and extent of a choroidal neovascular membrane prior to laser photocoagulation. More recently, indocyanine green (ICG) angiography, which was initially pioneered 20 years ago, has enjoyed a come-back. This technique images the choroidal circula-tion using wavelengths in the infrared region and can be useful in cases where the limits of the neovascular membrane are obscured by haemorrhage.13 Although theoretically promising, the practical usefulness of ICG angiography remains limited.

4.2.4 Genetic factors in AMD

AMD is a disorder of complex inheritance. Numerous studies have now shown that genetic predisposition is important in AMD, but that this is likely to be modifi ed signifi cantly by environmental factors. Until 3–4 years ago, studies on the genetics of AMD were

Figure 4.2 Late-phase fl uorescein angiogram of an extensive subfoveal choroidal neovascular membrane in ‘wet’ age-related macular degeneration. The white arrow indicates the vessels in the neovascular complex, the white arrowheads indicate intraretinal haemorrhage and the black arrow indicates leakage of dye from the neovascular membrane.

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84

few in number and limited to several reports noting a positive family history of the condition in their patients. More recently, several workers have readdressed the question of genetic input in the pathogenesis of AMD. In a study comparing the characteristics of drusen (early clinical markers of AMD) in the spouses and siblings of affected patients with AMD, Piguet and co-workers14 revealed marked concordance between siblings but not between spouses, suggesting that genetic factors are more important than the environmental factors shared by spouses. Two other studies assessed the concordance of fundal changes for AMD in monozy-gotic and dizygotic twins.15,16 Both studies show a high rate of concordance for fundal fi ndings in AMD in the monozygotic pairs: 23 of 23 pairs in one study and 8 of 9 pairs in the other. As would be expected, the level of concordance for fundal fi ndings was much less striking in the dizygotic twins. Recently a case-control study by the authors concluded that the risk of developing AMD was 19 times greater for the sibling of an affected person than for the sibling of an unaffected control.17 More recently, several genome-wide scans have identifi ed several hotspots for AMD on the human genome. Over the past 12 months studies by several groups have shown that more than 50% of cases of AMD are caused by sequence changes in the genes controlling the pathway of the ‘complement’ cascade, which is involved in the body’s response to infl ammation. Although several potential genes have been implicated, the most important player seems to be comple-ment factor H (CFH). These are exciting fi ndings, which may in time offer signifi cant possibilities for advances in therapies.18

4.2.5 Treatment for AMD

At present, only 5% of patients with ‘wet’ AMD are treatable by argon laser photocoagulation. The position and nature of the cho-roidal neovascular membrane (CNVM) is critical when assessing the feasibility of treatment. Extrafoveal CNVMs respond well to conventional laser (Fig. 4.3), juxtafoveal CNVMs are variable in their response, whereas subfoveal CNVMs, on average, lose six lines of Snellen acuity after treatment. The position of these mem-branes is depicted in Figure 4.4. However, even those patients who respond to laser treatment with regression of the neovascular process have a recurrence rate over the next 3 years of 60%.19

CNVMs can be classifi ed as classical or occult. Classical mem-branes are those that are not obscured by blood or exudate and

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A BFigure 4.3 Treated extrafoveal CNVM (A) with corresponding post-treatment scotoma shown on an Amsler chart (B).

Figure 4.4 Position of CNVMs. FAZ, foveal avascular zone.

Position of CNVMs a - extrafoveal >200 μmb - juxtafoveal >1<199 μmc - subfoveal

a

b

cFAZ - 350 μmin diameter

Retinal capillariesin perifoveal area

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are completely visible on fl uorescein angiography. Classical membranes also fi ll early during fl uorescein angiography. Occult CNVMs are obscured by overlying blood or exudate, are poorly defi ned, and often fi ll slowly. Many other treatment modalities such as radiation therapy, photodynamic therapy (PDT), subreti-nal surgery, intravitreal and subtenon steroid injections, intravit-real anti-vascular endothelial growth factor (VEGF) aptamer and antibodies have been, and are currently being, evaluated.20–23 To date, PDT has been the most successful and is now recommended by the National Institute for Clinical Excellence (NICE) for patients with AMD-related 100% classical CNVM, whose vision is LogMAR 1.0 (6/60) or better. The evidence for benefi t for membranes other than 100% classical is said to be less strong. Treatment with PDT for this group of patients can be performed only within the confi nes of an approved centre. Detailed information can be found at http://www.nice.org.uk/pdf/49pressreleasepdt.pdf.

For patients with geographic atrophy, no specifi c treatment is available. Recent epidemiological studies suggest that those who eat diets high in lutein and zeaxanthin, and those who have higher levels of the antioxidant vitamins A, C and E, may have a reduced incidence of progression of the disease. The recent Age-Related Eye Disease Study (AREDS) supplementa-tion trial demonstrated a benefi t in terms of reduced progres-sion in patients with moderate drusen who had dietary supplementation.24

4.2.6 Visual prognosis

AMD is a clinically heterogeneous condition with a wide spec-trum of clinical manifestations. The visual prognosis therefore varies greatly depending on the disease subtype, as shown for different subgroups in Table 4.3.25,26 From a visual rehabilitation viewpoint, it is often in the early stages of neovascularisation, when vision is relatively good and metamorphopsia very dis-abling, that the condition is most diffi cult to manage. At this stage patients are often better using their spectacle correction, good lighting and large, high contrast, good quality print rather than magnifying aids. The patient’s willingness to accept low vision intervention and low vision aids can improve dramatically once they begin to focus attention on the degree of useful vision retained rather than the vision lost.

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4.3 Cataract

4.3.1 Prevalence

The term cataract describes the opacifi cation of the crystalline lens of the eye. The type and position of the opacifi cation can vary greatly; however, from the patient’s viewpoint, it is the degree of visual compromise that is important. Owing to the multifactorial aetiology of cataract, the true incidence is diffi cult to assess. Data from the Framingham Eye Study indicated a 5-year incidence of 10% at 55–59 years, increasing to 37% at 75–79 years.26 Others have

Table 4.3 Visual Prognoses in AMD

Fundal change Risk of visual loss

Hard drusen only (>8) 10% risk of CNVM in 5 years

Drusen with pigmentary changes 58% risk of CNVM in 5 years

Visual loss in a CNVM 60% of eyes show more than six lines of visual loss at 18 monthsa

Risk of second eye becoming involved 13% per yearby disciform scar

Risk of a PED developing a CNVM 25% at 10 years

Risk of a PED developing GA 75% at 10 years

Loss of central vision to <6/60 60% in 18 months[LogMAR 1.0] in a PED

Risk of a PED developing a ripb 4–10% in 18 months

Risk of PED in the second eye 80% in 3 years

The risk of a rip in the second eye 33% – year 1 60% – year 2 80% – year 3

Geographic atrophy Average interval between diagnosis and visual loss of 3/60 [LogMAR 1.3] is 9 years

a Reduced to 25% having more than six lines of visual loss in 18 months by argon laser photocoagulation.b Tear of the retinal pigment epithelium. CNVM, choroidal neovascular membrane; GA, geographic atrophy; PED, pigment epithelial detachment.

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reported senile lens changes to be present in 91% of the 75–85 years age group.27


The patient who is developing cataracts usually complains of gradual onset of blurred vision for distance. In contrast, reading acuity is usually well preserved and the acquired myopic shift may even cause the patient to boast that the eyes have improved as reading is now possible without the aid of reading glasses. Other symptoms include foggy or misty vision, glare that is typi-cally not improved by wearing sunglasses but is improved by shielding (i.e. by the use of hats or sun visors), and monocular diplopia or triplopia.

Most patients are assessed in the outpatient setting using a basic Snellen acuity chart. The Snellen chart, although very serviceable, has the disadvantage of measuring visual acuity at 95% contrast. Daily tasks, however, are not usually carried out at 100% contrast but rather in a setting of various shades of grey. Thus, it is hardly surprising that patients who are found to have 6/9 [LogMAR 0.2] vision by Snellen acuity may still complain that their quality of vision is poor. Although contrast sensitivity reduc-tion is not typical of all cataracts, some patients are signifi cantly disabled in low luminance situations despite having 6/6 [LogMAR 0.0] vision recorded on the Snellen chart.28 This is especially true for posterior subcapsular cataract.

Practical advice

If a patient complains of poor vision and diffi culty with daily tasks despite good visual acuity, measurement of contrast sensitivity will often reveal the patient’s true disability.

4.3.3 Treatment for cataract

Surgery for cataract is now an excellent procedure, with most units carrying out small incision phacoemulsifi cation day-case surgery under local anaesthesia. This is a painless, safe procedure with a low rate of complications. The most recent survey from the Royal College of Ophthalmologists (UK) is the National Cataract

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Audit, published in 1999, which reports the national outcomes for cataract surgery in the UK during 1997–1998.29 The results are as follows:

Of those with no ocular co-morbidity, 85% achieved a visual acuity of 6/12 or better on discharge from postoperative hospital follow up, while 65% of patients with a serious co-existing eye disease achieved this level of acuity at this time. At fi nal refraction, 92% of patients without ocular co-morbidity and 77% of patients with ocular co-morbidity achieved 6/12 or better visual acuity. The following main risk indicators were associated with visual outcomes and complications related to surgery: age, other eye diseases, diabetes and stroke, type of surgical procedure, and grade of surgeon. (p. 1)

4.3.4 Management of the patient with combined cataract and AMD

A diffi cult but common clinical problem is that of the patient with both AMD and cataract. Once a patient with reduced vision due to known AMD is told that they have a cataract, their hopes sore immensely, so much so that it is diffi cult to impress on them that the cataract may not be clinically signifi cant or that any surgical outcome will be tempered by the macular changes. However, if the cataract is clinically signifi cant, even if the macular changes are substantial, cataract extraction may be worthwhile in order to give the patient a brighter image with improved colour appreciation. The insertion of an intraocular lens is of paramount importance, as aphakic spectacles would result in compromise of the remaining good peripheral visual fi eld. Contact lenses are particularly useful in cases of monocular aphakia, most authorities encouraging daily wear as the preferred modality.

More recently an intraocular low vision aid has become avail-able. The Implantable Miniature Telescope (IMT) is a precision telescope consisting of micro-lenses that provide magnifi cation of 2.2–3×. The IMT is implanted in the capsular bag at the time of phacoemulsifi cation cataract surgery (Plates 7 & 8 [Fig. 4.5]). Although it is a useful tool in the management of low vision, patient selection and training are crucial for the successful use of this aid. As indicated by the National Cataract Surgery Survey 1998, 77% of patients with ocular co-morbidity achieved 6/12 [LogMAR 0.3] or better visual acuity.29

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4.4 Glaucoma

4.4.1 Chronic open angle glaucoma

Chronic open angle glaucoma (COAG) is a signifi cant cause of visual morbidity in our elderly population. From population surveys in the UK chronic glaucoma affects 0.8% of the population aged over 45 years and ocular hypertension affects approximately 9% of the population of the same age. COAG accounts for 9% of blind registrations in the UK. As COAG gives rise to no symptoms until the condition is advanced, the patient is usually unaware of the condition. Screening of at-risk populations is therefore impor-tant. The cardinal signs for diagnosis are raised intraocular pres-sure (IOP) (>21 mmHg), with either visual fi eld loss and/or optic disc cupping.

Practical advice

Assessment of the drainage angle by gonioscopy is important as chronic angle closure glaucoma (CACG) may masquerade as COAG.

The underlying pathological mechanism in COAG is abnormal resistance to fl ow in the trabecular meshwork – the cause of which remains unknown. Important risk factors for glaucoma include myopia, diabetes mellitus, hypertension and a positive family history. Genetic investigation of the glaucomatous process is now well under way. The candidate gene Trabecular meshwork inducible glucocorticoid responsive gene product (TIGR) has been shown to be responsible for some familial glaucoma.30,31 Several genetic loci are known for juvenile-onset glaucoma (OMIM #137750), adult-onset glaucoma (OMIM #137760), primary infantile glaucoma (OMIM #231300) and glaucoma-associated pigment dispersion syndrome (OMIM #600510).8

Treatment options for COAG are numerous, ranging from surgi-cal drainage with or without antimetabolites to retard healing, laser trabeculoplasty and drug therapy. Recently there have been several new additions to the medical management of COAG, reducing signifi cantly the need for surgical treatment.

Despite increased public awareness and meticulous screening by optometrists, some patients still present late for treatment. A

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further and rather diffi cult subset of patients is those with ‘normal tension glaucoma’. These patients present with typical glaucoma-tous fi eld loss and optic disc cupping but with normal IOP. It is important to be wary of the diagnosis of normal tension glaucoma in case a more sinister problem, such as a compressive neurologi-cal lesion, is overlooked.

Practical advice

The diagnosis of ‘normal tension glaucoma’ should be made only after all other possible diagnoses have been excluded.

4.4.2 Acute angle closure glaucoma

Acute angle closure glaucoma (AACG) characteristically presents in the elderly. In contrast to the asymptomatic patient with COAG, these patients are acutely unwell – so much so that they may be misdiagnosed as having an acute abdominal problem. The onset is rapid, although a full-blown episode can be pre-ceded by episodes of subacute angle closure that have aborted spontaneously. In retrospect, the patient may recall having noted episodes of blurred vision associated with coloured haloes around lights.

The symptoms of AACG include severe ocular pain with head-ache, a red eye and blurring of vision. As the pressure rises, the patient becomes progressively nauseous and then begins to vomit. Clinical examination reveals a red beefy eye and a mid-dilated pupil, often with a greenish hue. The cornea may be oedematous and the eye stony hard to touch. After treatment and resolution of the attack, areas of lenticular infarction (glaucomenfl ecken) may become apparent. These indicate previous episodes. Medical therapy should be started immediately and, once the IOP has settled, treatment should be completed by bilateral peripheral iri-dectomies or laser iridotomies.

Patients who are hypermetropic and who have enlarged cata-ractous lenses appear to be most at risk. The incidence of AACG varies depending on race. An overall incidence for Caucasians is 0.1%; however, a recent study from France reported an incidence of 3.8 per 100 000 population.32 AACG, if treated promptly, should not lead to visual impairment.

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4.4.3 Visual prognosis and the implications

One of the most diffi cult issues to deal with when speaking to the glaucomatous patient about rehabilitation concerns mobility and driving. Whereas the patient with moderate to advanced bilateral AMD generally recognises that visual loss is likely to make driving hazardous, particularly in conditions of poor visibility, those with glaucoma are often oblivious to fi eld loss and unaware of the risks until such time as they are involved in an accident or have a ‘near miss’. Low vision aids and advice on alternative eye movement strategies will not help with mobility tasks, including driving, and advice on the legal consequences of driving with impaired vision must be given. For all other central visual tasks, advice on lighting, contrast and, in particular, the use of contrast enhancement will prove benefi cial.

4.5 Diabetic retinopathy

Diabetic retinopathy, in particular maculopathy, is a cause of sig-nifi cant visual morbidity in the elderly. By the age of 60 years, most patients with insulin-dependent diabetes mellitus (IDDM) and proliferative retinopathy have usually reached a stable state – be it that of bilateral regressed neovascularisation and good central vision following laser treatment, or of long-term poor vision due to maculopathy. Patients with type 2 diabetes may require ongoing treatment for maculopathy. A summary of the fi ndings in diabetic retinopathy is given in Chapter 3.

4.6 Central retinal vein occlusion


Central retinal vein occlusion (CRVO) presents with sudden blur-ring of vision in one eye. Most patients with CRVO are aged 50 years or more, and 50–70% suffer from hypertension, diabetes mellitus or cardiovascular disease. A recent study on risk factors for CRVO33 reported an increased risk for CRVO with systemic hypertension, diabetes mellitus and open angle glaucoma. Treat-ment of these conditions has no effect on ocular complications, although meticulous treatment of the underlying condition can

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prevent complications as well as CRVO in the second eye.33 The risk of CRVO is reported to be decreased by increased levels of activity and increased levels of alcohol consumption. In women the risk of occlusion was found to be decreased with use of post-menopausal oestrogens and increased with a higher erythrocyte sedimentation rate. Cardiovascular disease, treatment for diabe-tes, lower albumin/globulin ratios and higher γ-globulin ratios are associated with higher risk of ischaemic versus non-ischaemic CRVO. Systemic hypertension is a risk factor for both ischaemic and non-ischaemic CRVO.

The clinical fi ndings in patients with CRVO fall within a spec-trum ranging from mild to severe. The mildest changes are those of venous stasis with dilated veins and widespread dot and blot haemorrhages; the most severe are those of a profoundly isch-aemic retinal vein occlusion where massive intraretinal haemor-rhages, multiple cotton-wool spots, prominent disc swelling and retinal oedema are present. The prognosis and complications in these eyes are directly proportional to the degree of ischaemia present, and CRVO is therefore classifi ed into two groups: isch-aemic and non-ischaemic. From a clinical viewpoint it is thus necessary to assess the degree of capillary non-perfusion in each patient and to determine whether poor central vision is due to macular non-perfusion and damage to the retinal pigment epithe-lial cells or due to macular oedema. Figure 4.6 outlines the clinical assessment and management of CRVO. Approximately 30% of CRVOs are non-perfused or ischaemic, and neovascular glaucoma ensues in 40–60% of these. At the onset of CRVO, the iris vessels may be dilated; however, this sign is not necessarily indicative of rubeosis iridis.

4.6.2 Laser treatment of CRVO

Controversy regarding the need for prophylactic photocoagulation (PRP) of ischaemic CRVOs for the prevention of neovascular glau-coma has existed for some time. The Central Retinal Vein Occlu-sion Study, which reported in 1995, was designed to answer two questions:34

1 Is PRP useful in preventing iris neovascularisation and neovascular glaucoma in eyes with CRVO?

2 Does grid laser help in terms of visual acuity in CRVO?

The study group concluded:34

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• Iris neovascularisation – prophylactic PRP does not totally prevent iris and angle neovascularisation and prompt regression of neovascularisation is more likely to occur in eyes that have not been treated previously. It is therefore recommended that laser should be applied only at the fi rst sign of iris neovascularisation.

• Macular oedema – although grid laser photocoagulation for macular oedema in CRVO was associated with angiographic evidence of a reduction in macular oedema, there was no improvement in vision. Grid laser for macular oedema in CRVO can therefore not be recommended.

4.7 Temporal arteritis


Temporal arteritis is the ophthalmic presentation of a systemic disease.35,36 The patient usually presents with sudden loss of vision, sometimes preceded by episodes of amaurosis fugax. The visual loss is usually unilateral with the second eye becoming affected in a matter of hours to days. The patient seldom

Figure 4.6 Clinical management of CRVO. VA, visual acuity.

CRVO

30% Ischaemic(>10DD of retinal non-perfusion)

70% Non-ischaemic(<10DD of retinal

non-perfusion)

Neovascularisation

Iris new vessels with neovascular glaucoma

40–60%(Laser only when

new vessels appear)

Retinal neovascularisation10%

(Laser only whennew vessels appear)

Macular oedema(Grid laser doesnot improve VA)

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volunteers systemic symptomatology, although, when probed, symptoms such as malaise, temporal headache, jaw claudication, proximal muscle weakness, loss of appetite and weight loss, and fever become apparent. The clinical fi ndings include an afferent pupillary defect, red desaturation, depression of sensitiv-ity in the affected visual fi eld, and optic disc pallor and swelling, usually in a vertical pattern. The differential diagnosis of the patient who presents with a swollen optic disc is outlined in Figure 4.7. Some 12% of patients with temporal arteritis are reported to have diplopia.

The crucial investigation is the erythrocyte sedimentation rate (ESR), which is usually greater than 100 mm/h. In 5% of patients, however, this can be normal, in which case, if the history and clinical fi ndings are suggestive, a diagnosis of temporal arteritis should be made. The C-reactive protein test often shows a positive result. Once the diagnosis has been made clinically, corticosteroids in a dose of 80–100 mg orally or intravenously should be started immediately, as the fellow eye can be affected simultaneously or very soon after the fi rst eye. A temporal artery biopsy should be carried out within 48 hours of starting steroids.

Practical advice

Temporal arteritis is an ophthalmic emergency as loss of vision can be prevented in the second eye if treatment is started promptly.

4.7.2 Visual prognosis

Once the vision has been lost, recovery is unusual, although occa-sionally the most recently and less affected eye can improve slightly. As sequential involvement of the fellow eye is the rule, early diagnosis is crucial in order to prevent blindness in the second eye. The late or misdiagnosis of this condition is particu-larly tragic as visual loss and severe visual impairment is dis-tinctly preventable in many of these patients. Occasionally, patients with refractory disease require treatment with steroid-sparing immunosuppressants to control the disease process. Rehabilita-tion in these cases usually involves sensory substitution, as optical aids and low vision advice are of limited value.

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4.8 Central retinal artery occlusion


Occlusion of the central retinal artery (CRAO) presents with sudden unilateral painless loss of vision. The cause, especially in the elderly, is usually embolic, with a common source being the carotid arteries.37 CRAO is often preceded by episodes of amauro-sis fugax (temporary loss of vision in one eye). The typical clinical appearance of a CRAO is of retinal pallor with a cherry-red spot at the macula. Intraretinal haemorrhage is usually minimal. If the cause is embolic, the embolus is usually visible and lodged at an arterial bifurcation. Less common aetiologies include occlusive disorders such as temporal arteritis, collagen vascular diseases and syphilis. If the embolus is lodged in a more peripheral artery, visual fi eld loss may be sectorial.

Investigations are usually limited to clinical examination with cardiac and carotid artery auscultation, and an ESR measure-ment to rule out temporal arteritis. The presence and severity of carotid artery disease can be quantifi ed by carotid doppler studies.

4.8.2 Management of central retinal artery occlusion

CRAO is an ophthalmic emergency. If the embolus can be dis-lodged within the fi rst hour, the visual loss can be lessened. Emer-gency measures include:

• Digital massage• Intravenous acetazolamide• Inhalation of a 95% oxygen–5% carbon dioxide mixture• Anterior chamber paracentesis (reduction of intraocular

pressure by the removal of aqueous humour).

In practice, however, the patient either presents late or the em-bolus is impossible to dislodge despite these measures. As with many of the conditions mentioned in this chapter, a fundamental role of the optometrist is to be vigilant for signs and symp-toms indicative of second eye involvement and to initiate rapid re-referral.

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Practical advice

As the risk of permanent blindness following amaurosis fugax is approximately 10% in 5 years and the risk of stroke is 20% in 5 years, these patients should be investigated urgently. Some hospitals offer a rapid access TIA (transient ischaemic attack) clinic.

4.9 Anterior ischaemic optic neuropathy

Anterior ischaemic optic neuropathy (AION) is due to arteritic or non-arteritic occlusion of the posterior ciliary arteries.38 Loss of vision is sudden and usually progressive for 24–48 hours. The most common causes include temporal arteritis (10%) and non-arteritic atherosclerotic optic neuropathy. Patients with arteritic optic neuropathy tend, on average, to be 10 years older than those with the non-arteritic form. The non-arteritic form is more common in men, in contrast to the arteritic type, which is more prevalent in women. Coronary bypass and cataract surgery have also been implicated in the pathogenesis of AION. Management of the arte-ritic form of AION is as for temporal arteritis. There is no proven effi cacious management of the non-arteritic type.

4.10 Cerebrovascular accidents and visual function

Cerebrovascular accidents are a signifi cant cause of visual dis-ability. The most common sign is homonymous hemianopic or quadrantopic visual fi eld loss, although oculomotor abnormalities and perceptual irregularities may also be present. Sometimes a patient can present with visual symptoms being unaware that he or she has had a cerebrovascular event. After excluding ophthal-mic pathology, it is imperative that the patient be referred for investigation of the stroke. During the recovery phase of a stroke it is important that ophthalmic symptoms and signs are not over-looked. A signifi cant proportion of patients will have diffi culty with vision due to uncorrected refractive errors, wrong glasses being worn during rehabilitation, diplopia and progressive co-morbidities such as AMD, diabetic retinopathy, glaucoma and cataract.39 It is imperative that information on ophthalmic status

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and the magnitude of visual impairment is provided to those responsible for overall medical and rehabilitation management, as these problems will complicate other aspects of rehabilitation management.

4.11 Low vision management of the elderly

Low vision management of the elderly has to be seen within the context of their overall health status. Those who have age-related ophthalmic pathology in the absence of other health problems often do very well with conventional illuminated stand magnifi ers and portable hand magnifi ers, provided they have come to terms with vision loss and the fact that new spectacles or surgery will not reverse the condition. As motivation and confi dence in han-dling improves, spectacle magnifi ers and telescopic aids can be added to the armoury. Those who were avid readers may fi nd a CCTV or Easyreader system invaluable. Those with complex health problems, and in particular age-related degeneration of the higher functions, will fi nd low vision aid usage diffi cult. Elderly confused patients with Alzheimer’s disease cannot use low vision aids, and their families need to be advised on practical, high contrast, colour and size issues. Those with handling problems such as arthritis of the hands or spine need ergonomically suitable low vision aids. However, those with Parkinson’s disease may benefi t from a spec-tacle mounted device and a reading stand.

It is important to remember that almost all elderly people, before the onset of visual impairment, will have been used to wearing distance and/or reading glasses or bifocals. The refractive error does not disappear with the onset of visual impairment, although it may become insignifi cant. Advice on the need for, and use of, spectacles needs to be given carefully.

4.12 Summary

The elderly visually impaired are the group that optometric prac-titioners deal with most. In this group, the visual impairment is often asymmetrical and for some time unilateral. Most patients cope well with this situation, although occasionally some patients fi nd it diffi cult to accept. Those who develop bilateral problems vary greatly in their ability to cope. Some manage very well and

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simply adjust their lifestyle and use visual aids with great motiva-tion whilst accepting their limitations. A small minority are never able to come to terms with their problem and often retreat into their homes and lead a lonely isolated existence. Important factors in success in using visual aids include family and social support and the patient’s general health and motivation.

References

1. Weale RA. The ageing eye. London: Lewis; 1963. 2. Aclimandos WA, Galloway NR. Blindness in the city of

Nottingham (1980–1985). Eye 1988; 2:431–434. 3. Thompson JR, Du L, Rosenthal AR. Recent trends in registration of

blindness and partial sight in Leicestershire. British Journal of Ophthalmology 1989; 73:95–99.

4. Goldberg J, Flowerdew G, Smith E, Brody JA, Tso MO. Factors associated with age-related macular degeneration. An analysis of data from the fi rst National Health and Nutrition Examination Survey. American Journal of Epidemiology 1988; 128:700–710.

5. DeBlack SS. Cigarette smoking as a risk factor for cataract and age-related macular degeneration: a review of the literature. Optometry 2003; 74:99–110.

6. Klein ML, Francis PJ. Genetics of age-related macular degeneration. Ophthalmology Clinics of North America 2003; 16:567–574.

7. Kahn HA, Leibowitz HM, Ganley JP et al. The Framingham Eye Study. II. Association of ophthalmic pathology with single variables previously measured in the Framingham Heart Study. American Journal of Epidemiology 1977; 106:33–41.

8. Friedman DS, O’Colmain BJ, Munoz B et al. Eye Diseases Prevalence Research Group. Prevalence of age-related macular degeneration in the United States. Archives of Ophthalmology 2004; 122:564–572.

9. Coffey AJH, Brownstein S. The prevalence of macular drusen in post-mortem eyes. American Journal of Ophthalmology 1986; 102:164–171.

10. West SK, Rosenthal FS, Bressler NM et al. Exposure to sunlight and other risk factors for age-related macular degeneration. Archives of Ophthalmology 1989; 107:875–879.

11. Green WR. Clinicopathologic studies of senile macular degeneration. In: Nicholson DH (ed.) Ocular pathology update. New York: Masson; 1980:115–144.

12. Jacob A, Prasad S, Boggild M, Chandrate S. Charles Bonnet syndrome; elderly people and visual hallucinations. British Medical Journal 2004; 328:1552–1554.

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13. Yannuzzi LA, Slakter JS, Sorenson JA, Guyer DR, Orlock DA. Digital indocyanine green videoangiography and choroidal neovascularization. Retina 1992; 12:191–223.

14. Piguet B, Wells JA, Palmvang IB, Wormald R, Chisholm IH, Bird AC. Age-related Bruch’s membrane change: a clinical study of the relative role of heredity and environment. British Journal of Ophthalmology 1993; 77:400–403.

15. Meyers SM. A twin study on age-related macular degeneration. Transactions of the American Ophthalmology Society 1994; 92:775–843.

16. Klein ML, Mauldin WM, Stoumbos VD. Heredity and age-related macular degeneration. Observations in monozygotic twins. Archives of Ophthalmology 1994; 112:932–937.

17. Silvestri G, Johnston PB, Hughes AE. Is genetic prediposition an important risk factor in age-related macular degeneration? Eye 1994; 8:564–568.

18. Bok D. Evidence for an infl ammatory process in age-related macular degeneration gains new support. Proceedings of the National Academy of Sciences of the United States of America. 2005;102(20):7053–7054. Epub 2005 May 10.

19. Macular Photocoagulation Study Group. Five-year follow-up of fellow eyes of patients with age-related macular degeneration and unilateral extrafoveal choroidal neovascularization. Archives of Ophthalmology 1993; 111:1189–1199.

20. Chakravarthy U. Radiotherapy for choroidal neovascularisation of age-related macular degeneration: a fresh perspective. Eye 2000; 14:151–154.

21. Harding S. Photodynamic therapy in the treatment of subfoveal choroidal neovascularisation. Eye 2001; 15:407–412.

22. Verteporfi n Roundtable Participants. Guidelines for using verteporfi n (Visudyne) in photodynamic therapy for choroidal neovascularization due to age-related macular degeneration and other causes: update. Retina 2005; 25:119–134.

23. Eyetech Study Group. Anti-vascular endothelial growth factor therapy for subfoveal choroidal neovascularization secondary to age-related macular degeneration: phase II study results. Ophthalmology 2003; 110:979–986.

24. Hammond BR Jr, Johnson MA. The Age-Related Eye Disease Study (AREDS). Nutrition Reviews 2002; 60:283–288.

25. Klein R, Klein BE, Moss SE, Cruickshanks KJ. The Wisconsin Epidemiologic Study of Diabetic Retinopathy: XVII. The 14-year incidence and progression of diabetic retinopathy and associated risk factors in type 1 diabetes. Ophthalmology 1998; 105:1801–1815.

26. Leibowitz HM, Krueger DE, Maunder LR et al. The Framingham Eye Study monograph: an ophthalmological and epidemiological

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study of cataract, glaucoma, diabetic retinopathy, macular degeneration, and visual acuity in a general population of 2631 adults, 1973–1975. Surveys in Ophthalmology 1980; 24(Suppl):335–610.

27. Sperduto RD, Seigel D. Senile lens and senile macular changes in a population-based sample. American Journal of Ophthalmology 1980; 90:86–91.

28. Elliott DB, Bullimore MA, Patla AE, Whitaker D. Effect of a cataract simulation on clinical and real world vision. British Journal of Ophthalmology 1996; 80:799–804.

29. Desai P, Minassian DC, Reidy A. National cataract surgery survey 1997–8: a report of the results of the clinical outcomes. British Journal of Ophthalmology 1999; 83:1336–1340.

30. Raymond V. Molecular genetics of the glaucomas: mapping of the fi rst fi ve ‘GLC’ loci. American Journal of Human Genetics 1997; 60:272–277.

31. Stone EM, Fingert JH, Alward WLM et al. Identifi cation of a gene that causes primary open angle glaucoma. Science 1997; 275:668–670.

32. Vadot E, Grateau C. The frequency of acute glaucoma crises. Implications for the detection of the risk of angle-closure. Bulletin des Sociétés d’Ophtalmologie de France 1989; 89:675–677.

33. Eye Disease Case–Control Study Group. Risk factors for central retinal vein occlusion. Archives of Ophthalmology 1996; 114:545–554.

34. Central Vein Occlusion Study Group. Evaluation of grid pattern photocoagulation for macular edema in central vein occlusion. Ophthalmology 1995; 102:1425–1433.

35. Hamilton CR Jr, Shelley WM, Tumulty PA. Giant cell arteritis: including temporal arteritis and polymyalgia rheumatica. Medicine 1971; 50:1–27.

36. Nordborg E, Nordborg C. Giant cell arteritis: strategies in diagnosis and treatment. Current Opinion in Rheumatology 2004; 16:25–30.

37. Fisher CM. Occlusion of the carotid arteries. Archives of Neurology and Psychiatry 1954; 72;187.

38. Cullen JF. Ischaemic optic neuropathy. Transactions of the Ophthalmological Societies of the UK 1967; 87:759–774.

39. Lotery ALW, Jackson AJ, Silvestri G et al. Correctable visual impairment in stroke rehabilitation patients. Age and Ageing 2000; 29:221–222.

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CHAPTER

Only part of the management of the visually impaired patient is technical in nature. A good knowledge of the availability of current hardware is essential, as is a sound clinical routine. At least as important is an understanding of the needs of the patient, their attitudes to visual impairment and an insight into ‘hidden agendas’ that may not be immediately apparent. The attitudes of the prac-titioner, and their motivations, are often ignored. There are other important parties involved – the patient is after all part of a family and a wider community.

The early literature on low vision concentrated on the hardware, and made the assumption that all patients had similar require-ments. It followed that, once the visual acuity was known, the calculation of the magnifi cation required was merely a matter of arithmetic, and the appropriate aid could be prescribed. Many patients adopted aids prescribed by such methods and used them most effectively. Others, with strong motivation, improvised for themselves, buying magnifi ers intended for hobbies or other uses

SECTION TWO

Low vision assessmentSection Editor: A. Jonathan Jackson

The psychology of low visionJanet Silver

555

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from retail outlets, or adapting spectacles or other optical instru-ments, and their own behaviour, as required. Over time it became apparent that a more clinical approach could provide the benefi ts of low vision care for a larger proportion of the population. The need for the low vision practitioner to have a deeper understand-ing of the issues involved in the rehabilitation process and the psychology of visual impairment have been addressed by Crossland & Culham.1

Much depends on the practitioner establishing a clear under-standing of the patient’s needs, and a good rapport with both patient and carer. That statement seems so self-evident as to be almost superfl uous, but in fact encompasses a considerable range of disciplines and the need for much examination of the dynamics of the behaviours of all involved in the matter – primarily the patient, but also carers, the community and the practitioner. Those who have successfully adapted to visual loss and the rehabilitative process consistently list the attitudes and behaviour of those responsible for the delivery of care to be crucial to the process.2

5.1 The image of visual impairment

The prevalence of visual impairment is described in Chapter 1. It has been shown that total blindness is a relative rarity and that the majority of visually impaired people have low vision. Low vision is, however, very poorly recognised, and even more rarely understood, by the community. Visual impairment is often per-ceived by the fully sighted as an either/or condition; one sees or one does not see. It has, however, been described more accurately by those with greater insight and understanding as ‘seeing through a series of veils or through smeared or broken window panes’.3 Typically, a person with low vision is likely to have one of the degenerative disorders, be female, elderly, have other disabilities, and quite likely to be alone at home for much of the time. Young, totally blind people are far more conspicuous, use a white stick or may be accompanied by an engaging guide dog. Less likely than elderly people to have other disabil ities, they are more likely to be employed, participate in shopping and have an active social life. It is therefore hardly surprising that the public image of a visually impaired person is of a totally blind and otherwise healthy young person, usually male. He is also expected to be compensated by particularly acute hearing and touch, be musical, very sensitive to

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emotional atmospheres, in possession of a sixth sense about danger, and have almost saintly qualities of patience and tolerance.

Blindness has often been seen as a curse and a punishment: ‘Damn your eyes!’ or ‘May I be struck blind if . . .’ Oedipus put out his own eyes as the ultimate manifestation of self-disgust. Writing in her autobiography One of the Lucky Ones about her early life in pre-revolutionary China, Lucy Ching claims that prostitution was suggested as suitable employment for a blind girl.4 The suggestion is that she was worth nothing better.

There are, of course, many myths about visual loss. Patients often talk of ‘saving their vision’ – as if it were a limited resource that could be exhausted. Another widespread belief is that use can in some way exacerbate the disease process. Love is said to be blind, the implication being that sound judgement is lost along with vision. Justice, too, has been referred to as blind.

All of this has had its effect on the attitudes of patients and the people with whom they must interact. Patients may feel stigma-tised by their impairment, and defi ned by it rather than by other characteristics: ‘the blind lady’ rather than ‘the red-haired lady at number 42’.5

5.2 The response to loss of vision

Attitudes to bereavement have been addressed in depth by Ameri-can psychoanalyst Elizabeth Kubler-Ross.6 It is generally accepted that the loss of a limb or a faculty, such as vision, is considered as a form of bereavement, with a similar response sequence. The process has been described as having fi ve stages: denial, grief, anger, depression and eventually acceptance. Alternative terminology has been used but the process of moving from a series of negative responses to more positive ones is almost universally accepted.

5.2.1 Denial

Denial shows itself in a number of ways. Typically, a patient with macular disease presents requesting ‘better glasses’, often after having been advised that the disorder is irreversible and untreat-able. While it is reasonable to assume that a person who has never had a refractive error corrected may not appreciate the difference between a relative scotoma and a poorly focused image, the same cannot be true for most patients with low vision, of whom the vast majority will have had to cope, at the very least, with presbyopia.

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Patients very reasonably seek a second opinion – less reasonably a third or fourth. Limited fi nancial resources are spent on spuri-ous treatments and medications. The best known examples are the nearly 100 so-called ‘cures’ offered in the last century for retinitis pigmentosa (AC Bird, personal communication). It is easy to understand that, in a disorder characterised by remissions, an uncertain prognosis and variable timescale, a remission may be attributed to an external event such as a new ‘treatment’. From the point of view of the low vision practitioner, the patient is unlikely to accept help while remaining convinced that a cure can be found. The practitioner’s explanations are viewed with scepticism, and often rejected. Those anticipating a miraculous cure may utilise simple hardware as an interim help whilst rejecting complex custom-made devices as unnecessary.

5.2.2 Grief

It is not easy to distinguish grief from depression. The patient is agitated, may weep a lot, apparently have a short attention span, talk in general terms about what they used to do, and revert con-stantly to what has been lost: ‘I used to do such a lot, now I can’t do anything.’

5.2.3 Anger

Anger is often easier to manage, though less easy to recognise. There appears to be a great need to blame someone for the situation; fre-quently this is a doctor, especially when underlying macular disease impairs outcome following cataract extraction. A spouse or parent or God may be blamed. More often, the disorder may be attributed to some event or behaviour, such as time spent on visually demand-ing tasks, ‘artifi cial’ light or, more recently computers. More reason-ably, diet or living in the tropics may be cited as causative factors. While this blaming may become an obsession, especially if it is believed that there is the possibility of compensation, at least the energy can often be channelled and used positively. Occasionally the anger is self-directed, and can literally be damaging.

5.2.4 Depression

Reactive depression often shows as passivity and dependency. The patient feels that they are totally helpless, worthless and power-less. They may well complain of disrupted sleep patterns.7 Where the grieving patient is agitated, the depressed one is calmer; they

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have given up, and either leave most of the talking to their escort or voice negative attitudes: ‘I am sure that you will not be able to help me’. The depressed patient stops taking a pride in their appearance. A woman once remarked: ‘Since I lost my sight I have disappeared. I am not there any more when I look in the mirror’. This response is often exacerbated if the practitioner addresses the carer, rather than the subject: ‘Does she take sugar?’

Recent studies highlight a strong association between visual loss in age-related macular degeneration (AMD) and depression.8,9 Rovner & Casten found a base rate prevalence of syndromal depression of 23% in newly diagnosed AMD patients; those most at risk having a pre-existing tendency towards neuroticism. This compared with ‘primary care’ and ‘community based’ rates amongst normally sighted elderly patients of 12% and 3% respec-tively.8 Williams et al highlight the extent of emotional distress associated with recent onset AMD and equate the associated decline in quality of life with that experienced by those diagnosed with obstructive pulmonary disease and cardiovascular disease.9 Results of a study on 6100 elderly women from Chicago have found a strong association between visual impairment and cognitive (odds ration 1.78) and functional (odds ratio 1.79) decline.10 When associated with dual sensory loss (hearing and sight loss) the odds ratios increased to 2.19 and 1.87 respectively.10 One particularly distressing recent fi nding concerns the link between visual impair-ment and suicide in the elderly. Waern et al, studying the link between disability and suicide in the elderly, found visual impair-ment carried an increased odds ratio of 11.4.11

5.2.5 Acceptance

Acceptance eventually comes to most patients. When told ‘This disorder never causes total blindness’, the patient with macular disease and a recent history of progressive deterioration prefers to believe the evidence of her own eyes than the assurances of the professionals. To hear the very same prognosis from a number of independent people is always helpful. The patient eventually fi nds that the vision is indeed stable, begins to discover that they have abilities as well as disabilities, and starts seeking ways to enhance them. It is at this point that the provision of low vision aids is most likely to be accepted. However, it can be contended that the accep-tance process may be precipitated or accelerated by low vision assessment and rehabilitation intervention.

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Practical advice

To handle any low vision consultation successfully, the practitioner must understand that the loss of vision involves a fi ve-stage bereavement process:

DENIAL, GRIEF, ANGER, DEPRESSION, ACCEPTANCE

People go through these stages at different rates, and to a different degree. It is, however, against this background that the practitioner commences the assessment. In this process, the effect of the dif-ferent disorders must be considered; certain diseases have an insidious natural history. Chronic simple glaucoma and retinitis pigmentosa cause a gradual reduction of fi eld, of which the patient may be totally unaware. Tiny adjustments are made over a long period, and the patient may present when the disorder is very advanced. This group of patients will have a modifi ed response. In contrast, disciform macular degeneration or central retinal vein thrombosis causes a dramatic loss, and patients fi nd themselves precipitated into a totally new situation where they have no infor-mation or experience on which to call. They feel unsafe and pow-erless. These are the patients in whom the bereavement process is most apparent; nevertheless, the more catastrophic the loss, once stable, the greater the potential that rehabilitative intervention will reap benefi ts and low vision aid usage will be considered.

5.3 The patient–practitioner relationship

In essence, the patient and practitioner enter into a contract:

Practitioner: I cannot restore the vision you have lost, but will do my best to help you utilise the vision you have retained and prescribe the best possible low vision aids.

Patient: I accept your offer of help, understand the limitations of my situation and the technology, and will do my best to cooperate.

Note that there are only two people involved. The contract cannot be made with a third party, although others, in particular carers and those with training in visual rehabilitation, may have a crucial role in initiating the process and providing support.12

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5.4 The case history

It is well worth investing a little time developing and learning an appropriate series of questions. These must be open enough to encourage a full disclosure of the information that you need, but specifi c enough to avoid wasting time on irrelevancies. For example, asking a patient ‘Please tell me about your problems’ will, if you are lucky, produce a complete ophthalmic history; if you are unlucky, you will hear the full medical history of the patient and her spouse, and an account of the shortcomings of family, friends and the government of the day! Far better is: ‘If we are to achieve the best possible outcome, we must establish exactly which tasks you need to manage’. The responsibility is shared by patient and practitioner, the tone is positive, and the concept of tasks is raised rather than problems.

Before task analysis, and assuming that diagnostic data are available, certain other aspects of the patient’s situation must be explored. It is helpful to know whether they live alone, with a partner, with other family members, or in an institution. Are they employed, seeking employment, or in education? Do they have other disabilities and how long have they been visually impaired? What help has been sought so far, and on whose initiative? Apart from these data, information will have been gained on the patient’s attitudes and the stage of the bereavement process that has been reached. People who are ‘grieving’ or ‘angry’ will need a little time to express their feelings. Tempting as it is to avoid the apparent irrelevance, to do so will confi rm to the patient that their situation does not warrant sympathy. Empathy, which indicates an insight into their feelings rather than an acknowledgement of sympathy, is more important. It is essential that the objectives remain clear and the patient is not allowed to take over the interview. After a short account, it is possible to interrupt with ‘I do understand how you feel about it, but we can do something to help’, and move on.

Practical advice

The successful low vision practitioner will possess both empathic understanding and clinical expertise.

Your questions and statements should always be worded so that you and the patient are comfortable with the vocabulary. It may

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be necessary to change gear between patients; your usual vocabu-lary will be incomprehensible to some and possibly seen as patro-nising by others. In low vision work, this sort of consideration of the patient’s needs is fundamental.

5.5 Task analysis

Some patients will announce that ‘I need to do everything’, and it is very diffi cult to get them to be more specifi c. It is necessary to explain that every device has slightly different characteristics, and none of them actually treats the underlying eye disease. Nonethe-less, despite claiming to understand, what the patient hopes for is a device that will restore normal vision.

The commonest task is reading, but here huge differences exist between patients giving the same response. Some will volunteer a desire to ‘read my correspondence and the newspaper’; however, for one patient that might mean the electricity bill and the headlines, whereas for another it is every word of a broadsheet, text on a com-puter screen and correspondence from a vast international network of friends’ writing on airmail paper. Supplementary questions that quantify and defi ne are needed. Which newspaper or magazines did you read before your sight got bad? Did you do the crossword? How do you reply to personal letters? Does someone else write for you? Do you use a felt-tip pen with heavily lined paper, a type-writer, or a computer? How many books did you read in a year? With a list constructed, the tasks should be prioritised; prescribing should normally address the fi rst priority in the fi rst instance.

Practical advice

Once the concept of the problem task has been understood, a list of priorities can be elicited and acted upon.

Occasionally a patient will have a fairly modest list: ‘Reading the occasional letter and the instructions on my medication is all that I really need’. As the assessment progresses and the desired acuity is achieved, other far more demanding tasks may be added. It is likely that the patient had no real confi dence in a positive outcome, and therefore did not take the risk of being disappointed. While it is entirely appropriate to suggest areas to the patient, care has

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to be taken not to create problems that do not exist: ‘How do you manage your correspondence?’ is completely legitimate; ‘Can you read the Bible?’ may not be.

A few patients will deny the existence of any problems: ‘I really don’t know why I’ve been sent to you – I manage very well, thank you’, and frequently they do! Possibly this is another aspect of denial; alternatively, the patient may have decided that the best strategy for dealing with the situation is simply to wish to do only the things that are possible. There is another more sinister possi-bility, often voiced as: ‘I will never be a burden on my children/carers’. The patient prides themselves on being uncomplaining, but may fi nd shopping and cooking so diffi cult that they become undernourished. It may be that they are fearful of testing the affec-tion of the people on whom they are dependent and running the risk that they will not bother, or merely that they consider their own needs to be less important. This sort of neglect often occurs when there are fi nancial pressures too, and family and friends with busy lives of their own happily collude.

5.6 Motivation

Motivation is closely associated with one’s ability to adapt and adjust to a new situation. This, in turn, is infl uenced by personality and one’s ability to deal with emotional stress.13

The best indicator of motivation is gained from questioning the patient about what they have done to alleviate the handicap. It is always rewarding to fi nd a patient who has discovered a magnifi er that gives access to large print and is looking for something better, or who is reading using the aphakic correction of a long dead rela-tive as a spectacle magnifi er. Conversely, the patient with a long-standing disability who does not have their glasses with them, or who fi nds the magnifi ers offered by helpers ‘completely useless’, is less likely to do well. Maintaining the status of being ‘blind’ may ensure the reward of extra attention from carers, and the investment is in remaining dependent.

Practical advice

Experienced practitioners agree that motivation is a crucial factor. Not every patient is motivated to make maximum use of their vision, and follow-up in the clinic or home is required to build on this.

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Some patients may have a hidden agenda, which is, in effect, an ulterior motive that contradicts the stated requirement. Some patients may use the onset of visual impairment to bring forward retirement on health grounds; conversely, the most highly moti-vated people are those who wish to continue in employment. They may, however, suffer a huge drop in confi dence of their own abili-ties, and need much reassurance. In fact, the more senior the post, the more important the decision-making abilities and the less important the visual acuity. The fi ling clerk has far greater problems coping with their day-to-day tasks than the managing director who has a secretary and PA at their disposal. It may be that some job restructuring is needed, but organisations are often very keen to keep experienced and competent staff. Commonly employees conceal the impairment – or believe that they do. More than one patient has found his admission of low vision accepted very casually by colleagues who were well aware of the situation, but respected the rights of the individual to privacy; usually the revelation is a relief to all concerned. It is important for the patient to appreciate that only their vision is reduced: the rest of their abilities are unimpaired.

5.7 Rejection

From the fi rst moments of the interview, the practitioner must hold their professional position as the person who provides informa-tion, advice, strategies and devices. The inexperienced practitioner may become angry with the patient who rejects the device that apparently achieves the targets. It is the practitioner’s responsibil-ity to offer the best advice; it is the patient’s right to reject it. The best response allows the patient the option of changing their mind without discomfort – it is advice and devices that are being rejected, not the practitioner. The patient may fi nd the use of low vision aids too demanding and prefer to use other modalities. Alternatively, the patient may still be in ‘denial’. In the latter case, the perma-nence implied by the adoption of complex or expensive devices implies a commitment that the patient is not yet willing or able to make. A useful strategy is to offer the best inexpensive magnifi er as ‘optical fi rst aid’, and encourage a fl exible follow-up regimen.

Some patients reject low vision aids because of their unusual appearance, for which many patients are completely unprepared. The practitioner is frequently told ‘What I want is ordinary glasses’,

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5.8 Family, friends and carers

Visually impaired children and their parents present very different problems. Children with congenital loss literally do not know what they are missing and, fi nding a task diffi cult, may simply opt out academically. They are very susceptible to peer pressure to conform to a current norm, and may reject low vision aids because they make them look and function differently. One adolescent patient remarked memorably: ‘I prefer people to know that I am partially sighted than to assume I am partially brained’. The parents, as well as coping with the extra burden of hospital visits and special mate-rials, carry a heavy burden of guilt in many cases, especially when the disorder is genetically determined or due to prenatal infl uences such as rubella. Eventually most seem to fi nd a balance between reasonable care and overprotectiveness, freedom to develop and unconcern. Counselling, including genetic counselling, helps.

Similar dilemmas can be observed in the companions and carers of other people with low vision. It is helpful for all concerned if a companion is present at the assessment, especially during the instruction period. An explanation of the nature of the impairment improves the ability of the companion to understand when help is needed. It can also provide valuable reinforcement of instruction and reiterate the demands imposed by a new appliance.

Another useful carer role is to maintain motivation. Many new users of low vision aids fi nd the learning process very demanding.

Practical advice

Ultimately the practitioner must overcome the temptation to equate rejection of advice and appliances with personal rejection. In so doing the door is left open to future help which can be provided through follow-up and review.

to which it is very tempting to reply, ‘Yes, but for those you need ordinary eyes!’ Such patients, unable to accept the image of them-selves with a device they perceive as stigmatising, prefer to keep the problem rather than the low vision aid. Sometimes, reminding the patient that they can control the situation, and that the device need be used only when they wish, for example when at home and alone, will result in a change of mind. The possession of the device effectively empowers the person.

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Eventually the use of the device becomes second nature, but in the early days more effort is expended on the device than the informa-tion being sought. An exact metaphor is a child learning to use a pen – the act requires great concentration, and the product is not easy to read. The experienced adult expends no energy on the process and interest is only in the data. Recently a 90-year-old woman related to the writer became a low vision patient needing a CCTV. Highly intelligent, she had no diffi culty understanding the process, but after a lifetime immersed in books was using the machine only for essential information. Regular encouragement from her family has her reading for pleasure again.

5.9 Handling failure

Inevitably, not every patient can be given the help they need, and the practitioner must come to terms with this failure. An under-standing of the factors that have been shown to have an impact on the success of low vision rehabilitation can be very helpful. Factors include ageing,14 duration of sight loss15 and the presence of other disability including hearing loss.10 There is an understandable tendency to give the patient something rather than send them away empty handed; this should be resisted. Of course, if the patient’s fi rst priority is to read price information in supermarkets, and the second to read their daughter’s letters written in 18-point strong black on white matt paper, then a magnifi er that allows N12 or N14 will be welcome if its limitations are explained. However, if the fi rst is newsprint, and the second is small instructions on prepared food packages, then N14 will be of little benefi t. Worse, the patient has an added burden, believing that if they make a greater effort they will succeed, confi rming any depressive posi-tion. The patient who cannot be offered a device should be told the truth, including the fact that both medicine and technology are making huge strides, and an appropriate device may become available. In the meantime, the patient should be directed to other sources of help.

5.10 Summary

Optimal low vision care can be delivered only if the practioner, experienced in clinical assessement routine and knowledgeable about low vision hardware and service availability, can empathi-cally help the patient to come to terms with the consequences of

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irreversible visual loss. The patient, who may well be only part way through the grieving process, needs to be amenable to help and must be encouraged to understand the extent and nature of help available. Motivation is required on the part of both so-called ‘signatories to the contract’, and both parties need to be able to build on the positive outcomes and get over those aspects of service provision that may be seen as failure.

References

1. Crossland MD, Culham LE. Psychological aspects of visual impairment. Optometry in Practice 2000; 1:21–26.

2. Kleinschmidt JJ. Older adults’ perspectives on their successful adjustment to vision loss. Journal of Visual Impairment and Blindness 1999; 93:69–81.

3. Kuusisto S. Planet of the blind. London: Faber & Faber; 1998. 4. Ching L. One of the lucky ones. London: Souvenir; 1980. 5. Goffman E. Stigma. New York: Touchstone; 1986. 6. Kubler-Ross E. On death and dying. New York: Touchstone; 1969. 7. Souhami RL, Moxham J. Textbook of medicine. London: Churchill

Livingstone; 1998. 8. Rovner BW, Casten RJ. Neuroticism predicts depression and

disability in age-related macular degeneration. Journal of the American Geriatric Society 2001; 49:1097–1100.

9. Williams RA, Brody BL, Thomas RG, Kaplan RM, Brown SI. The psychosocial impact of macular degeneration. Archives of Ophthalmology 1998; 116:514–520.

10. Lin MY, Gutierrez PR, Stone KL, et al. Vision impairment and combined vision and hearing impairment predict cognitive and functional decline in older women. Journal of the American Geriatric Society 2004; 52:1996–2002.

11. Waern M, Rubenowitz E, Runeson B, Skoog I, Wilhelmson K, Allebeck P. Burden of illness and suicide in elderly people: case-control study. British Medical Journal 2002; 324:1355–1358.

12. Stewart I, Joines V. TA today: a new introduction to transactional analysis. Nottingham: Lifespace Publishing; 1987.

13. Adams LL, Pearman JT. Emotional response and management of visually handicapped patients. Psychiatry in Medicine 1970; 1:233–240.

14. Wild JM, Wolffe M. Residual vision in the low vision patient. American Journal of Optometry and Physiological Optics 1982; 59:686–691.

15. Negrin S. Psychosocial aspects of ageing and visual impairment. In: Jose RT (ed.) Understanding low vision. New York: American Foundation for the Blind; 1983:55–59.

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The principles of refraction remain unchanged whether the patient is visually impaired or normally sighted. The refractive routine logically follows the recording of a comprehensive case history (medical, ophthalmic, visual, social, educational and employment) and task analysis, whereby patients are asked to outline the nature and extent of problems experienced. Attention must be paid to both the objective and subjective elements of refraction, as evi-dence suggests that between 8% and 10% of new patients referred for low vision consultations simply require an updated spectacle correction.1

6.1 Case history

Fundamental to the process of collecting a comprehensive case history is the need to draw out responses that will inform the process by which the patient is provided with helpful and appro-priate low vision aids and advice on visual rehabilitation. Patients must be helped to feel comfortable and at ease in the presence of the practitioner, and that the practitioner has a genuine interest in helping them deal with the problems resulting from visual impair-ment, and the clinical expertise to match. The psychological aspects associated with sight loss and with the interaction between patient and practitioner have been explored by Dodds et al2 and are also covered in Chapter 5.

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Questions on medical history must concentrate on relevant issues and be directed at disorders that are likely to produce con-founding disability (rheumatoid arthritis, Parkinson’s disease and multiple sclerosis) or preoccupy the patient’s thinking and thus impact on motivation (uncontrolled diabetes, terminal illness, psychotic illness). Interest in ophthalmic history should likewise focus on aspects of ocular health that are associated with visual impairment and the availability, or lack of availability, of medical and rehabilitative treatment (cataract, age-related macular degen-eration). In similar fashion, discussion of educational, employment and social issues should concentrate on areas affected by visual impairment and on the likelihood that help can be provided either directly through the clinic or via tertiary referral. Questioning on visual function will relate closely to the assessment of vision and is thus dealt with in Chapter 7, whereas discussion on task analysis and rehabilitation issues is to be found in Section 4.

Practical advice

Ensure that questions asked when recording the case history are those likely to elicit responses that will infl uence assessment procedures, prescribing and rehabilitation advice.

6.2 Current optical corrections

All existing spectacles should be assessed and the respective pre-scriptions recorded. Patients should be asked to comment on the degree of usefulness, or lack of it, that they attribute to each pair of glasses. Apparently idiosyncratic responses should be recorded and subsequently addressed. The patient who claims that glasses that are worn constantly are ‘absolutely useless’ may be encourag-ing the practitioner to prescribe a minimal change in the hope that new glasses will be synonymous with improved vision. Alterna-tively, the patient may simply feel undressed without glasses that have been part of their attire for as long as they care to remember. Confi rmation should be sought as to the origin of the spectacles, as a signifi cant proportion of elderly visually impaired persons resort to using other people’s glasses in the hope that they may be of more use than their own. Elderly patients often become

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confused as to which glasses they should be using for different visual tasks.

All existing low vision aids should be categorised and, again, patients should be asked to outline their uses. As many as 50% of patients referred for a low vision consultation already have one or more magnifi ers.3 Patients should be encouraged to bring existing aids to subsequent clinical appointments as often they are reticent to demonstrate home-made or personally acquired devices to a person whom they perceive as an ‘expert’ in the fi eld.

Monocular distance acuities should be recorded, at appropriate working distances, through the most appropriate glasses, using charts from the selection outlined in Chapter 7. Only in cases where the prescription is minimal, or where the patient claims that existing glasses are useless, is there any real benefi t in assessing unaided acuities. Near acuities should be recorded both through the reading glasses and through existing aids, as used in the manner demonstrated by the patient. Contact lens wearers should have their lenses assessed and be encouraged to attend their contact lens practitioner for regular aftercare. Regular wearers will undoubtedly wish to use low vision aids in conjunction with exist-ing contact lenses. An accurate over-refraction should confi rm that they are appropriately powered. A baseline refraction should nonetheless be undertaken during the course of a subsequent visit.

6.3 Retinoscopy

Obtaining an accurate retinoscopy result is essential if the fatigue and distress caused to the patient by a protracted and diffi cult sub-jective routine is to be minimised. Accuracy will, of course, depend on the clarity of the media, the nature of any uncontrolled eye move-ments and patient cooperation. In diffi cult cases the procedure will be improved considerably by ensuring that the retinoscope is serviceable and the batteries are fully charged. A rechargeable instrument with a halogen bulb will prove invaluable.

In those cases where medial opacities are signifi cant, reducing or eliminating background illumination can be benefi cial and reveal a refl ex that was previously indistinguishable. The tech-nique of ‘radical retinoscopy’, which involves the use of reduced working distances, to improve image brightness, may also prove benefi cial.4 Similar effects can be achieved in patients with central

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medial opacities, by moving off axis. In both circumstances care must be taken to compensate for the apparent prescription changes induced. Any off-axis cylindrical components detected must be confi rmed subjectively. Understandably, full-aperture trial lenses prove advantageous in these circumstances. Cycloplegic refraction may assist in optimising a retinoscopy refl ex in an eye with medial opacities. This should, of course, be undertaken as a matter of course when refracting phakic children attending the clinic as new patients. Care should be taken to occlude the dominant eye when refracting a strabismic fellow eye.

Throughout the course of the retinoscopy examination it is imperative that the patient be provided with an appropriate fi xa-tion target and that those with nystagmus be allowed to utilise head tilt or turn to minimise movement. ‘Near retinoscopy’, using illuminated targets attached to the retinoscope, can prove an extremely useful technique when estimating the accommodative potential in unresponsive children and those with learning disabilities (Fig. 6.1).5,6

Figure 6.1 Dynamic retinoscopy using a custom-made, internally illuminated, target. (Reproduced from Jackson & Saunders 19996 with kind permission of Blackwell Publishing.)

Practical advice

An elusive retinoscopy refl ex may be tamed in an eye with medial opacities by performing ‘radical retinoscopy’ at a reduced working distance, in virtual total darkness.

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6.4 Keratometry/corneal topography

Although rarely used during the course of the routine low vision assessment, keratometry can help confi rm the presence of high degrees of astigmatism alluded to on retinoscopy. Keratometry can also confi rm the presence of irregular astigmatism, a fi nding that may be particularly benefi cial when refracting visually impaired patients with a severe learning disability. Some 20% of patients with Down’s syndrome, for example, are likely to exhibit keratoconus (Fig. 6.2 [Plate 9]).7

Figure 6.2 (Plate 9) Corneal topographical maps illustrating the difference between regular with-the-rule astigmatism (upper panel) and keratoconus (lower panel). The steep, inferiorally positioned, cone in the lower panel gives rise to a distorted scissor-like retinoscopy refl ex, irregular astigmatism and a progressively increasing myopic refractive correction.

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6.5 Subjective routine

Before commencing the subjective refraction, ensure that the trial frame is both comfortable and appropriately fi tted in such a way as to resemble the fi nal spectacles. Vertex distance, pantascopic tilt, and both horizontal and vertical centration should all be optimal. As a general rule, the spherical lenses should be posi-tioned in the back cell of the trial frame with cylindrical ones in front. As stated previously, full-aperture trial lenses are desirable, in this case because they allow the examiner to assess eye move-ments and fi xation as the patient undertakes both distant and near tasks. A refractor head (phoropter) is entirely inappropriate in this respect. In certain circumstances it may be appropriate to refract over existing glasses in order to demonstrate more clearly whether any refractive change recorded is signifi cant. In these cases a Halberg trial clip should be used.

6.5.1 Distance vision

Once an appropriate chart has been selected from the wide range of those available to the practitioner (see Ch. 7), attention should be paid to the optimal working distance. The emphasis should be on eliciting a positive and encouraging response from the patient as it is disconcerting for the patient to be presented with a letter chart and realise that they can barely see the largest letter. Those with visual acuities of less than 1.0 LogMAR (6/60 Snellen) should be presented with charts at distances of 1–3 metres, whereas those with acuities of between 0.6 and 1.0 LogMAR (6/24 and 6/60 Snellen) should use working distances of 3–4 metres. Six-metre charts should be used only for those whose acuities are better than 0.6 LogMAR (6/24 Snellen).

Throughout the subjective examination the practitioner must use consistent and clear terminology. Patients fi nd many of the tests diffi cult enough without having to respond to ambiguous questions. When working from a reliable retinoscopy result, initial modifi cation to the spherical component should be made in rela-tively gross steps (±2.00/±5.00). Attempts should be made to encourage patients to make forced-choice decisions. In those cases where the ocular media are not clear and a reliable retinoscopy result is not forthcoming, larger steps may be utilised in the early stages (±10.00/±20.00). High degrees of uncorrected refractive

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error may simply never have been detected by previous examin-ers. As patient confi dence in the decision-making process grows and responses improve, smaller steps can be used (±1.00/±0.50). There is rarely any point in using ±0.25 steps when assessing a visually impaired patient.

Assessment of the cylindrical component of the refraction is best done using a ±1.00 DC Jackson Cross Cylinder with appro-priately chosen targets. For this purpose a hand-held Landolt C Acuity Test Chart Panel can prove invaluable. Circular targets are not always present, especially on the more recently produced loga-rithmic charts, Us or Ds may, however, suffi ce. Initially, modifi ca-tions to the cylinder axis should be made in 20° steps, whereas power modifi cations should be made in ±1.00 steps. In certain circumstances it may be appropriate to allow the patient to assume control of the rotating cylinder, although elderly patients and those with restricted upper limb movements or poor manual dexterity may fi nd this diffi cult.

In theory, subjective testing should be less time consuming than when performed on normally sighted patients, as fi ne tuning may not be possible. In practice, the low vision practitioner must invest more time and energy in the patient, as throughout the course of the examination it is important to show empathy with the patient. Only when patients believe that the examiner really cares about both them and the outcome of the examination will optimal results be achieved.

As a general rule an updated prescription should not be issued until it can be clearly demonstrated that an improvement of two lines or more on a LogMAR acuity chart can be achieved through the new correction.4 Those with acuities of less than 1.0 LogMAR (6/60 Snellen) are unlikely to appreciate a spherical change of less than 1 dioptre or a cylindrical change of less than 2 dioptres. Those with signifi cant medial opacities may in addition fi nd it more diffi cult to discriminate defocus than pati-ents with macular pathology. This phenomenon has been attri-buted to the respective gradients of the frequency of seeing curves. Final distance acuities should be recorded in a manner consistent with the instructions given with individual charts (see Ch. 7).

The practitioner may wish to conclude the distance refraction with a pinhole acuity check, but it must be borne in mind that those with central scotomas often fi nd this test diffi cult. Perfor-mance may be improved by using multiple pinholes. The stenopic

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slit may, on rare occasions, assist the practitioner in the search of the cylindrical axis in keratoconus.

Practical advice

Changes in prescription of less than ±1 DS or less than ±2 DC are unlikely to signifi cantly benefi t the patient with low vision.

Changing serviceable spectacles on the basis of a prescription change alone should generally be contemplated only if an improvement of at least two lines on a LogMAR chart can be demonstrated.

6.5.2 Near acuity

Near acuities, as determined by word reading charts (see Ch. 7), should be recorded through both existing reading glasses and a standard +4.00 reading addition over the optimised distance prescription.

The +4.00 addition is chosen arbitrarily, as it provides unit mag-nifi cation when the object is placed at the least distance of distinct vision (25 cm). This working distance may also represent a psy-chological barrier to the optometrist unfamiliar with low vision. Practically, most visually impaired patients, including the elderly, can be encouraged to use a working distance of 25 cm for reading if benefi t can be demonstrated to them. Younger patients may understandably choose to utilise accommodation in preference to a near addition, although near acuities should still be recorded at a 25-cm working distance, as well as the patient’s accustomed working distance.

Adequate auxiliary lighting should be available in the form of an anglepoise lamp. Patients must be encouraged to adjust both the lamp to work surface working distances and the angle of inci-dence of the light. The Chartered Institution of Building Service Engineers’ code recommendations are that casual readers should utilise a surface illuminance of 150 lux, whereas more dedicated readers, and those involved in sewing, should use up to 300 lux. Recommendations for elderly patients are that illuminance levels should be increased by 50–100%.8 During the course of the near-acuity assessment, note should be taken of both reading speed and accuracy, both with and without occlusion and using optimal and suboptimal illumination. Formal methods for assessing reading

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speed and for comparing oral and textual comprehension recall skills are available, but are generally used only as research tools.9

A number of methods are available by which the near add required to achieve a given acuity can be calculated.10 The actual acuities achieved are, however, often slightly poorer than pre-dicted. Most methods are based on the magnifi cation ratio (MR = Near acuity recorded through a given add/Near acuity required). The predicted addition required to achieve the desired near acuity thus becomes the product of the magnifi cation ratio and the reference add used to determine the present near acuity. The magnifi cation ratio is, in reality, the ratio of the size of the letters read through the standard add to the size of the letters that the patient wishes to read.

Practical example

A 74-year-old patient using optimal reading glasses incorporating a +4.00 addition achieves N10 print in appropriate lighting at a working distance of 25 cm. His desire is to read N5 newsprint.

Magnifi cation ratio = 10/5 = (×2)

Predicted add = 2 × 4 = 8 dioptres

The process of working through increased near additions in +4.00 steps and thus gradually building up the strength of the ‘spectacle magnifi er’ in the trial frame can be extremely helpful as it gradu-ally acclimatises the patient with low vision to the concept of the reduced working distance and associated diffi culties.

Similar calculations can be performed using the Sloan M Series, Keeler A Series and Bailey Lovie Acuity Charts. As was the case for distance acuities, near acuities should be recorded both mon-ocularly and binocularly. It must, however, be noted that the pre-dicted add required to achieve text of any given size is ‘predicted’, and thus practical confi rmation is required.

6.5.3 Binocularity

Although the vast majority of visually impaired patients do not have normal binocularity, many are convinced that it is to their

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benefi t to function under binocular conditions. This is usually not a problem when considering distance requirements. In those cases where binocularity can be demonstrated and where the acuities recorded in the fellow eye are similar, base-in prism can sometimes be applied to facilitate comfortable fusion at near. The rule of thumb derived from Lebensohn’s rule11 is to incorpo-rate base in-prism to both the right and left lenses, equivalent to the strength of the near addition. The individual using spec-tacle magnifi ers with a +10.00 addition would therefore require 10 prism dioptres base-in right and left. Manufacturing limitations ensure that the maximum add through which binocularity can be achieved is +12.00. Individuals incapable of binocularity must be made aware of the benefi ts of monocular occlusion and reassured that occlusion will not lead to the deterioration of vision in either the occluded eye as a result of underuse, or the preferred eye through overuse. Binocular vision tests, including the use of fogging lenses and duochrome, are generally unhelpful in low vision practice.

6.6 Prescribing options

6.6.1 Spectacles

In deciding whether to convert the refractive fi ndings into a pre-scription, consideration must be given not only to the actual improvement likely to be achieved through a change in prescrip-tion but also to the lens form and design of the appliance. Bifocals incorporating a +4.00 addition may prove diffi cult for the elderly patient, whereas the aphakic child may adapt easily to these for general purpose work. Working distances and the characteris-tics of the desired task must also be considered as, for example, a +4.00 addition may be entirely inappropriate for bench work even though it improves the acuity substantially over the original +2.00 addition.

The problem of illuminating a work surface at 25 cm must also be considered, as elderly patients may fi nd it diffi cult to evade the shadows cast in the home environment. The instability of the underlying refraction in, for example, patients with corneal grafts and those with diabetic retinopathy may cause the practitioner to defer prescribing until such time as confi rmation of the result can be achieved.

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6.6.2 Contact lenses

Many patients enquire about contact lenses as if these were magical appliances that, if prescribed, will alleviate the problems imposed by visual impairment. In reality, contact lenses are often benefi cial in low vision only when fi tted to visually impaired keratoconics or those with irregular corneae. High myopes may also benefi t from the increased retinal image size achieved in comparison with spectacles. In aphakics, contact lenses may assist with fi eld expan-sion, although this is at a cost as they lose the magnifi cation (20%) induced by a highly positive lens mounted in the spectacle frame. Contact lenses have, in addition, been used as the ocular in contact lens telescopes, although reported success has been limited.

Patients with a highly myopic refractive error lose their inbuilt ‘uncorrected’ near proximal magnifi cation when fi tted with dis-tance contact lenses. Visually impaired children who have a high degree of refractive error may, however, gain great personal con-fi dence from being able to dispense with thick unsightly glasses.

6.6.3 Refractive surgery

Practitioners must be prepared to advise on the indications and contraindications of corneal refractive surgery, as visually impaired patients with a signifi cant refractive error may pursue these new procedures in the vain hope that they will not only eliminate the need for spectacles but also cure visual impairment. Practitioners should also be prepared to enter into discussion with surgical col-leagues on the optimal choice of intraocular lens power for those listed for cataract surgery. The high myope, for example, may well be most appropriately left undercorrected in order to ensure that unaided near acuities remain usable. Knowledge of the availabil-ity of intraocular implantable telescopes and the postsurgical rehabilitative process associated with their use should also be sourced (Fig. 6.3).12

Practical advice

Visually impaired patients have the same right to fashionable and serviceable eye wear as the normally sighted. Provided the patient understands that a new correction may not improve acuity, do not deny the patient the opportunity to obtain a new correction if they so desire.

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6.7 Summary

Obtaining accurate refraction results is fundamental to the success of any low vision consultation. Existing techniques must, however, be modifi ed to achieve an optimal result. Most importantly, pa-tients must feel that the practitioner has a full understanding of their needs and a genuine desire to help. Attention should be paid to recording distance and near acuities using appropriate charts, working distances and illumination.

References

1. Jackson AJ, Silver JH, Archer DB. An evaluation of follow up systems in two Low Vision Clinics in the United Kingdom. In: Woo GC, ed. Low vision: principles and applications. Berlin: Springer; 1986:396–417.

2. Dodds AG, Bailey P, Pearson A, Yates L. Psychological factors in acquired visual impairment: the development of a scale of adjustment. Journal of Visual Impairment and Blindness 1981; 75:306–310.

3. Wolffsohn JS, Cochrane AL. The changing face of the visually impaired. The Kooyong Low Vision Clinic’s past, present and future. Optometry and Vision Science 1999; 76:747–754.

4. Bailey IL. Refracting low vision patients. Optometric Monthly 1978; May:519–523.

Figure 6.3 Implantable miniature telescope. The Vision Care Implantable Telescope consists of a silica glass, 4.4 mm long, optical cylinder mounted in a black PMMA Haptic with support loops (weight 45 mg). The miniature telescope, together with the cornea, essentially constitute a Gallilean telescope system, providing magnifi cation of approximately ×3 over a 6° central visual fi eld.

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5. Woodhouse JM, Meades JS, Leat SJ, Saunders KJ. Reduced accommodation in children with Down’s syndrome. Investigative Ophthalmology and Visual Science 1993; 34:2382–2387.

6. Jackson AJ, Saunders KJ. The optometric assessment of the visually impaired infant and young child. Ophthalmic and Physiological Optics 1999; 19:S49–S62.

7. Haugen OH. Keratoconus in the mentally retarded. Acta Ophthalmologica 1992; 70:111–114.

8. Chartered Institution of Building Service Engineers. Code for interior lighting (5th edn). London: Chartered Institution of Building Service Engineers, Lighting Division; 1984.

9. Lovie-Kitchin JE, Bowers A, Woods RL. Oral and silent reading performance with macular degeneration. Ophthalmic and Physiological Optics 2000; 20:360–370.

10. Wolffsohn JS, Eperjesi F. Predicting prescribed magnifi cation. Ophthalmic and Physiological Optics 2004; 24:334–338.

11. Lebensohn JE. Practical problems relating to presbyopia. American Journal of Ophthalmology 1949; 32:22.

12. Alio JL, Mulet EM, Jose M, Ruiz-Moreno JM, Sanchez MJ, Galal A. Intraocular telescopic lens evaluation in patients with age-related macular degeneration. Journal of Cataract and Refractive Surgery 2004; 30:1177–1189.

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The way we perceive the environment in which we live is deter-mined by the nature of the complex stimuli and the manner in which these stimuli are subsequently processed by our sensory system. Our interpretation of visual images is infl uenced by our ability both to resolve high contrast detail and to discriminate low contrast features, colour differences, brightness and depth, and to utilise information from the full extent of our panoramic fi eld of vision. Any attempt to quantify visual functions must thus be capable of assessing the impact that defi cits in any of these pro-cessing mechanisms may have on the quality of our visual images. With this in mind, this chapter considers the assessment, not only of distance acuity, but of near acuity, contrast sensitivity, colour vision, visual fi elds and glare sensitivity.

7.1 Visual acuity (high contrast/distance)

7.1.1 Distance acuity charts

Visual acuity is the assessment of the fi nest spatial detail that the visual system can resolve. Over the past 140 years, a range of charts, the majority of which use optotype test targets, has been developed for the assessment of visual acuity (Fig. 7.1). These charts have different characteristics and adhere to different design strategies (Table 7.1).1

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Snellen acuity charts

Historically, visual acuity has been assessed using the Snellen chart,2 which has been extremely successful in screening for common causes of visual impairment and the detection of uncor-rected refractive error. The Snellen chart does, however, have inherent weaknesses in that it uses an irregular geometric pro-gression from top to bottom, thus reducing its sensitivity in the upper (6/60 [1.0 LogMAR] to 6/24 [0.6 LogMAR]) range. Within the context of the low vision clinic, this is the region most neces-sary when assessing visually impaired patients. A secondary weakness is that the chart fails to deal with the phenomenon of ‘crowding’ or ‘contour interaction’, which results in single-letter identifi cation tasks being much easier to undertake than those involving multiple-letter presentations. Furthermore, the legibility ratings given to the wide range of letters used on the traditional Snellen chart differ greatly. This is a particular problem at the upper end of the chart [1.0 LogMAR (6/60) to 0.6 LogMAR (6/24)], where very few letters are presented.

The impact of design features, including font styles and letter selection, has been reviewed extensively by Bennett,3 whose work informed the fi rst British Standards publication on test types in

Figure 7.1 Selection of high-contrast visual acuity charts: a, Bailey–Lovie LogMAR; b, Early Treatment of Diabetic Retinopathy Study (ETDRS); c, modifi ed Snellen; d, Keeler A series; e, Sonksen Silver; f, Sheridan–Gardner.

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1968.5 Finally, the conventional method of recording acuity mea-sures from the Snellen chart (6/6 part, 6/7.5+, etc.), when individ-ual letters on any given line are missed, is insensitive and somewhat arbitrary. It is for these reasons that considerable work has been devoted, over the past 30 years, to developing visual acuity charts that are more appropriate, particularly in the fi eld of low vision.

Table 7.1 Visual Acuity Chart Design Characteristics

Snellen chart Bailey–Lovie chart

Origins 1862 Herman Snellen2 1976 Ian Bailey & Jan Lovie4

Relevant BS 4274-1 (1968)5 BS 4274-1 (2003)6

standards BS 4274-1 (2003)6

Optotype Letter dimension: 5 × 4 Letter dimension: 5 × 4 characteristics grid grid Legibility rating: 0.92–1.10 Legibility rating: 0.90–1.1 Letter style: sans serif Letter style: sans serif Letters used: 10 Letters used: 12 Letters per row: 1 (6/60) Letters per row: 5 to 8 (6/5)

Scoring Snellen fraction i.e. 6/12 LogMAR value i.e. 0.30 methods (or Snellen decimal 6/12 Letter scoring: 0.02 units = 0.5) per letter (i.e. 0.26 = Letter scoring: +/− 6/12+2) (i.e. 6/12+2)

Progression Lines per chart Lines per chart: 14 Original: 7 Geometric progression Current: 8–10 Uses standardised letter Arithmetic progression and row spacing: multiplication factor × 1.2589

Recorded test 6 metres – variations 6 metres (20 ft USA) – distance expressed in Snellen recalibrate scale for denominator alternative distance

Alternative Range of historical and Keeler A series,7 ETDRS,8

designs current charts using Sloan9

various font styles

Currently available charts fall broadly into two categories: those based on the original Snellen2 premise and those designed according to the principles advocated by Bailey & Lovie.4

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Keeler A series charts

This chart was designed by Charles Keeler with the specifi c inten-tion of creating a chart that would be particularly useful in the assessment of visual impairment.7 The A series charts, based on a logarithmic (constant ratio) scaling system, were essentially the precursors to all currently available LogMAR charts. They had 20 different series of letters, ranging from A1 (6/6 [LogMAR 0.0] equivalent) to A20 (1/60 [LogMAR 1.9] equivalent). Each line dif-fered from its nearest neighbour, in size, by a factor of ×1.25. The charts were supplied with easy-to-use conversion tables that enabled low vision practitioners to determine the magnifi cation levels required to assist patients achieve a desired level of acuity. Near equivalents, also calibrated in A series format, could be used in a similar manner, as they were calibrated according to the diop-tric power of the near addition required to achieve an improve-ment in near acuity at a reference working distance of 25 cm.

Sloan distance acuity charts

An American equivalent to the Keeler chart, the Sloan distance acuity chart was also designed with the needs of the visually impaired in mind.9 This chart, which uses the ‘M’ or metric series notation, has never achieved worldwide usage. The system is best known for its use in the assessment of near acuity. Letters of size 1M, which are about the same size as lower-case newsprint, subtend an angle of 5 minutes of arc when located 1 m from the eye. The system is linear so that 3M letters are exactly three times larger than the 1M letters. Test distances and letter sizes can be recorded in Snellen format with a 3M letter read at 20 cm recorded as 0.2/3M.

Bailey–Lovie charts

Fundamental to the success of the Bailey–Lovie chart in low vision practice is its logarithmic scale and the inclusion of equal numbers of similarly legible letters on each line of the chart.4 The gaps between letters, and indeed between lines, are determined by the size of the letters used on each line. On the scale chosen, any change of three lines represents a doubling, or alternatively halving, of letter size. Visual acuity is scored as 0.1 LogMAR for each row and 0.02 LogMAR for each letter named correctly.

The main advantage of the chart is that it, and its near vision equivalent, greatly simplify the process of calculating the esti-

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mated magnifi cation required by a patient interested in reading text of a specifi ed size. As LogMAR defi nes a visual angle, not the size of the letters, the score must be adjusted for the distance of the chart. LogMAR scores decrease with improved acuity (the opposite to decimal acuity). The most recent (2003) British Stan-dard on visual acuity test types6 incorporates LogMAR notation and a modifi ed range of optotypes (Fig. 7.2).

Figure 7.2 The Bailey–Lovie LogMAR chart, designed for use at 6 metres. Figures in the left margin of the chart and lower left insert indicate letter size in Snellen metric and Snellen feet. Figures in the right margin and lower right insert indicate letter size in LogMAR and VAR ratings. The lower scale lines indicate how LogMAR and VAR scores should be adjusted when testing is carried out at different distances.

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Waterloo charts

Similar in design and concept to the Bailey–Lovie charts, the letters on these Canadian charts are oriented such that letters of equal size are placed in columns rather than rows.10 Patients are advised to read across the top line (row) until they reach a point where mistakes are made, whereupon vertical checks are made to determine the exact acuity. An additional feature of the Waterloo chart is the inclusion of interactive surround bars, which ensure that letters at the start and fi nish of each line are as diffi cult to read as those within the lines.

Ferris LogMAR charts

The most widely used of the LogMAR charts is the Early Treat-ment of Diabetic Retinopathy Study (ETDRS) chart, an American chart designed by Ferris, Kassoff, Bresnick and Bailey,8 which uses Sloan optotypes. The designers recommend that one chart is used during the course of refraction and that the other two charts are used (one each) when determining the optimal acuities of the right and left eye. Results are recorded in conventional format, although the chart is designed for use at 4 m. Essentially, ETDRS

Practical advice

These examples indicate how LogMAR acuity values are specifi ed when using the standard 6 m Bailey–Lovie chart at three different working distances:

Performance LogMAR acuity

6-m test distance Patient reads top three 0.6 − 0.04 = 0.56 lines plus two letters out of fi ve on line 4

Chart moved to Patient now reads top six 0.3 − 0.04 = 0.263 m lines plus two letters out + working distance of fi ve on line 7 conversion factor of 0.3 = 0.56

Chart moved to Patient now reads top 0.0 − 0.04 = −0.041.5 m nine lines plus two letters + conversion factor of out of fi ve on line 10 0.6 = 0.56

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charts and Bailey–Lovie charts are of the same design, but differ in the actual letters used.

Symbol charts

As the prevalence of visual impairment is greatest in population subgroups with severe learning disabilities, it is important for the specialist low vision practitioner to have knowledge of, and access to, a selection of symbol and optotype matching charts. Although many of these charts have been developed for paediatric use, they are equally useful when assessing the visual status of those with learning disability. The system designed by Lea Hyvarinen, a Finnish ophthalmologist, includes LogMAR-based alpha numeric and picture symbol charts, matching symbols, single symbol books and crowded symbol books.11 Symbol matching is under-taken in much the same way as when using Sheridan–Gardner letter matching cards and Kay picture cards (Fig. 7.3).

Computer-generated charts

The potential to assess visual acuity using electronic technology is both exciting and carries some important advantages. Not only

Figure 7.3 Selection of symbol and single-letter charts used in the assessment of visual acuity in children and adults with learning disabilities: Kay pictures, illiterate E, Sheridan–Gardner single-letter cards, Sonksen Silver crowded letter cards and Fuchs symbols.

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can optotype sequences be varied and randomised, thus eliminat-ing the possibility of target memorisation, but the accuracy of measurements can be enhanced by presenting greater numbers of targets of any given size. Target luminance, contrast, spacing, exposure time and so forth can all be adjusted. Until recently, test chart design was limited by pixellation: to achieve reasonable shape fi delity, letters need to be at least 10 pixels in height. If a line of 6/3 (−0.3 LogMAR) letters were 100 pixels long, then a line of 6/60 (1.0 LogMAR) letters would need to be 2200 pixels long. Verti-cal restraints are less signifi cant as scrolling is a viable presenta-tion strategy. Affordable display technology is now approaching an appropriate level of sophistication, and a useful development is the Test Chart 2000 system (Fig. 7.4 [Plate 10]).13

7.1.2 Distance acuity specifi cations

Visual acuity measurements can be expressed in a number of ways, the most universally accepted of which is the Snellen frac-tion notation in which the numerator ‘d’ is the test distance and the denominator ‘D’ is the distance at which just resolvable letters

Figure 7.4 (Plate 10) The Thomson Test Chart 2000 computer-generated visual acuity assessment system. (Courtesy of Professor D Thomson; reproduced with permission from Macnaughton 2005.12)

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must be placed so as to subtend an angle of 5 minutes of arc at the eye (d/D or 6/60). In the USA, measurements are expressed in feet as opposed to metres (6/60 = 20/200 [LogMAR 1.0]). The main benefi t of expressing acuities in this manner is that there can be no confusion over the testing distance at which acuities are recorded.

The decimal notation, as used throughout most of Europe, is obtained simply by dividing the numerator by the denominator (6/12 = 0.5 [LogMAR 0.3]). Specifi cation of acuity in this way is, however, regrettable as results can easily be confused with LogMAR results, which are unrelated. Alternative methods of specifying acuity are according to the minimal angle of resolution (MAR), which is obtained by inverting the Snellen fraction and expressing the result in minutes of arc (6/24 → 24/6 → 4 min of arc). LogMAR is simply the logarithim to the base of 10 of the ‘MAR’ (6/6 = MAR 1 = LogMAR 0). Alternative methods of expressing LogMAR acuity measures are as visual acuity ratings14 or visual effi ciency ratio values.15

The benefi ts of using LogMAR scales and acuity charts have already been identifi ed. A comparison of the various acuity mea-surements is given in Table 7.2. In cases where visual acuities are extremely poor, it has become common practice within the UK to use the term counting fi ngers (CF) as an indicator of poor vision. This should be discouraged as fi nger width, distance from the patient, fi nger separation and target–surround contrast vary greatly. Those with acuities of less than 0.5/60 [LogMAR 2.0] can be classifi ed as having hand movements (HM) vision, if indeed movement can be detected. Where movement cannot be detected, vision should be classifi ed as either perception of light (PL) with or without directional sensitivity, or as no perception of light (NPL). Less than 5% of the visually impaired population will fall into the latter category.

Practical advice

If working in a clinical environment where a combination of acuity charts is routinely used by a combination of practitioners, errors in comparing data can be avoided if, alongside every acuity measurement, note is made of test distance and chart type.

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Low vision assessm

ent

13

8

Table 7.2 Comparison of a Variety of Visual Acuity Designations

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M

7A

ssessment of visual function

77139

Table 7.2 Comparison of a Variety of Visual Acuity Designations —cont’d

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M


140

7.2 Visual acuity (low contrast)

Contrast sensitivity, despite the fact that its relevance in detecting ocular disease has been apparent since the 1960s,18 has until re-latively recently been perceived by many in routine optometric practice as too diffi cult to assess within a conventional clinical environment. This perception is unacceptable, as the vast majority of our visual interaction with the world involves resolving low contrast detail. Table 7.3 illustrates the variation in contrast, inher-ent in a range of everyday tasks undertaken by adults and children.

7.2.1 Low contrast acuity charts

The contrast detection threshold, as determined using sine wave gratings, is of course the reciprocal of the contrast sensitivity func-tion (CSF). When considering the CSF and how it is affected by the disease process, it is important to remember that conventional high contrast optotype acuity is represented along the x-axis

Table 7.3 Contrast Threshold Required to Achieve Fluent Text Reading and ‘Spot’ or ‘Survival’ Reading When Undertaking a Range of Visual Tasks Involving Subject Matter with Different Contrast Ratings

Visual task Task Contrast threshold (%)

contrast

Fluent reading Survival reading

DSE display 100 <10 <33

Quality magazine 80 <8 <27

Newsprint 70 <7 <23

Old paperback 50 <5 <16book

Blackboard 30 <3 <10

For the individual who needs to read (high contrast) video output material fl uently, the contrast reserve ratio needs to be 10 : 1, i.e. the contrast threshold should be 10% of the actual video display contrast. To spot-read text on the same screen, a task that is less demanding, the contrast reserve needs to be only 3 : 1, i.e. the contrast threshold needs to be only 30% of the actual video display contrast. (Data from Rumney16 and Whittaker & Lovie-Kitchin.17) (DSE, Display Screen Equipment.)

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(spatial frequency) where 6/6 [LogMAR 0.0] equates to 30 cycles per degree, and 6/12 [LogMAR 0.3] to 15 cycles per degree. Con-trast, which is expressed as a percentage, is represented on the y-axis. The human visual system is most sensitive in the 3–5 cycles per degree region (Fig. 7.5). In recent years, a number of clinical and research tests have, however, become available (Arden grating test, Regan low contrast letter chart, Vistech VCTS chart, Cam-bridge gratings, Pelli–Robson letter chart and Melbourne edge test), all of which claim to quantify the visual system’s ability to discriminate contrast. Computerised technology, as referred to above (see Computer-generated charts), can also be used to present various combinations of low contrast optotypes in sequences

Pelli-Robson

Low-contrast VA

High-contrast VA

Spatial frequency

Con

tras

t sen

sitiv

ity

Figure 7.5 The normal human contrast sensitivity curve (contrast sensitivity/spatial frequency) upon which a grid of Es of various sizes and contrast levels has been superimposed. The three highlighted blocks illustrate the sizes and contrast values of letters used on the 10% Bailey–Lovie, Snellen/high contrast Bailey–Lovie, and Pelli–Robson charts. (Reproduced with permission from Harvey & Franklin 2005.19)

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identical to those used in the presentation of high contrast targets.13 Many of these tests are, however, inappropriate within the context of the low vision clinic. The Regan and Pelli–Robson charts, together with Bailey–Lovie low contrast charts, are, in the authors’ opinion, most useful within the low vision context (Fig. 7.6).

Regan low contrast letter charts

A series of three charts designed according to LogMAR principles are available. Each line on the chart is made up of eight equidistant letters. Interline distances are, however, not standardised. The three charts are quoted as having contrast ratings of 96%, 7% and 4%, and are designed for use at 3 metres. It is particularly impor-tant to ensure that low contrast charts are uniformly illuminated to a level of approximately 100 cd/m2. A nonogram scoring system is available.20

Pelli–Robson low contrast letter charts

These charts consist of letters of equal size but of varying con-trast. Letters of similar contrast are grouped in threes, with two groups per line over a total of seven lines. Contrast decreases from 89% in the top left to 0.5% in the bottom right, in 0.15 Log units.

Figure 7.6 Selection of charts used to assess contrast sensitivity and low contrast acuity within the conventional clinical setting: a, Ginsberg vision contrast test system; b, Bailey–Lovie 10% contrast chart; c, Pelli–Robson chart; d, Cambridge low contrast gratings.

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The score attributed to the patient is the logarithm of the contrast sensitivity of the last group of three letters, of which at least two were read correctly. The chart, when used at 1 metre, is designed to assess contrast sensitivity at the peak of the contrast sensitivity function curve, and is probably best placed to correlate with daily living activities in which reduced contrast sensitivity is likely to cause disability (mobility, face recognition, reading).21

Bailey–Lovie low contrast charts

Bailey–Lovie charts are commonly available on white plastic panels that have a high contrast chart (black letters) on one side and a low contrast chart with grey letters on the other. The design of the high and low contrast charts is the same. The contrast of the low contrast chart is 10% Michelson (18% Weber). The difference between the high and low contrast visual acuities recorded on the two charts provides a measure of the slope of the contrast sensitiv-ity function (CSF) as it approaches the individual’s high spatial frequency cut-off. Even for patients who have signifi cantly reduced contrast sensitivity, this high frequency section of the CSF is ap-proximately linear.22

Symbol charts

The Lea Test system, referred to in the section on Symbol charts above, includes a set of low contrast charts with symbols of 10%, 5%, 2.5% and 1.25%. The symbols are exactly the same as those used on the high contrast charts, with the result that the same set of matching cards and symbols can be used when testing young children and those with a learning disability.11 More recently, pae-diatric contrast sensitivity screening cards have been developed. Those developed by both Hyvernan (the Hiding Heidi set) and Bailey (Mr Happy Faces) use smiling faces to construct tests that can measure low contrast acuity down to contrast levels of 1.25% and 0.25% respectively (Fig. 7.7).

Practical advice

When assessing optimal contrast sensitivity using optotype-based letter charts, participants must be given additional time to recognise the letters as temporal summation is required to achieve results approaching threshold.

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Edge detection tests

Rectangular luminance profi les (edges) are thought to relate well to real-world objects as they consist of a range of spatial frequencies detected by the most sensitive spatial channels, the peak of the contrast sensitivity curve. The Melbourne edge test (MET) is a com-pact chart consisting of three main parts: a hand-held portable lightbox, a printed transparent acetate, and a response key card. Each circle is divided by a luminance edge so that a contrast dif-ferential is established between the two halves. The observer must identify the orientation of the edge (0°, 45°, 90° or 135° alternative forced choice) with successive circles decreasing in contrast.24

Sinusoidal grating tests

These tests, when produced as printed cards, are generally used for screening purposes. Only by using expensive computer-generated gratings can a comprehensive plot illustrating the full relationship between spatial frequency and contrast sensitivity be obtained. This is important when determining the specifi c impact of cataract, amblyopia and other forms of ocular pathology on visual function.

Figure 7.7 Happy Faces paediatric contrast sensitivity symbol charts. (Reproduced with permission from Harvey & Gilmartin 2004.23)

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The computer-generated test is, however, less useful within the low vision environment, where the practitioner generally wishes to use low contrast testing facilities to determine the relationship between specifi c aspects of disability and reduced visual functions. Hess, who has reported extensively on computer-generated contrast sen-sitivity measures, advises caution when interpreting the results of contrast sensitivity testing on patients with low vision, as results may be erroneously affected by scotoma site and depth.25

One grating-type test that is available as hard copy is the Arden test,26 which uses plates in which the contrast of the grating increases as one moves down the plate. The task for the patient is to identify, as the plate is gradually withdrawn from its envelope, the point at which the gratings fi rst become visible. The Vistech (VCTS) chart uses an alternative approach involving the presenta-tion of fi ve rows of circular targets on which gratings have been superimposed. There are thus targets of fi ve different spatial fre-quencies, each of which is presented at nine contrast levels. The observer in this case has to identify the orientation of gratings on each line.27 Reeves et al28 have expressed concern about the repeat-ability of these tests. The Cambridge gratings use a square wave design of fi xed spatial frequency (four cycles per degree) and dif-fering contrast (between 5% and 0.14%).

7.3 Practical relevance of contrast sensitivity

When working in the low vision clinic, contrast sensitivity testing can be carried out more easily using optotype-based tests, which are familiar to the patient. In many cases, the dramatic difference experienced when switching from a high contrast Bailey–Lovie chart to the 10% equivalent helps the patient gain greater under-standing of the nature of their visual impairment and why certain adaptive strategies should be implemented to maximise vision. Patients with glaucoma and medial haze, for example, often describe their view of the world as ‘faded’, ‘grey’ or ‘washed out’ to a degree that is out of proportion with their level of disability, as detected using high contrast optotypes. These patients are often relieved to be shown a clinical test that equates results to their experience.

7.4 Distance testing strategies

Within the context of the low vision clinic, it is essential that accurate and repeatable measures of visual acuity and, when indicated, low

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contrast acuity or contrast sensitivity are obtained. This information is fundamental not only to the process of determining the range of low vision aids that will be demonstrated to the patient, but also in advising the visually impaired patient on rehabilitation strategies that may be used when tackling a range of far and intermediate dis-tance tasks. Room lighting should be standardised and the test routine outlined as described in Chapter 6. Most importantly, patients must be given time to discriminate optotype detail, and positive feedback from the practitioner usually encourages an optimal result.

7.5 Visual acuity (near/reading)

At the outset it must be stressed that, although the term ‘near acuity’ is often quoted when describing the visual performance of patients tested using conventional Faculty of Ophthalmology-approved near vision charts, the measurement is not the near equivalent of distance acuity, irrespective of whether distance acuity has been recorded using Snellen or LogMAR-type charts. The reasons for this are threefold. First, distance acuity testing generally utilises upper-case single optotypes that, in the case of LogMAR charts, are separated both horizontally and vertically by distances equal in size to the optotypes. Virtually all near charts use either lower-case unrelated words or continuous text pro-duced using a range of letter and word layout spacings. Second, distance acuity testing requires the patient either to name letters or to match letters or symbols, whereas at near patients are required to make sense of the letters and pronounce what they see as a recognised word, a task that requires higher-order cortical pro-cesses. Third, this process is even more complicated as the task of ‘reading’ involves not only pronouncing individual words, but also altering delivery to refl ect meaning and context. The process of comprehending what has been read will, of course, also be infl uenced by reading speed, which is infl uenced by eye move-ment control. It is for this reason that the authors advocate the term ‘reading acuity’, which is an entirely appropriate function to measure, as assistance with reading is, indeed, the stated goal of the majority of patients attending low vision clinics.29

7.5.1 Reading performance

Many recent research studies have investigated the relationship between reading acuity/performance/speed and other quantifi -

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able aspects of visual function (distance visual acuity/contrast sensitivity/scotoma size and density), and subjected the outcome values to fairly complex multivariable analysis.30 The results have, however, simply confi rmed that it is diffi cult to accurately corre-late reading ability with any single measure of visual function and, if one wishes to know how well one can read either with or without the help of a low vision aid, one must at the very least assess reading speed and possibly comprehension.

A clinical interpretation of many of these data can be drawn from work published by authorities in the fi eld, including Whittaker & Lovie-Kitchin17,31 and Rumney.16 These individuals stress the importance of ‘fl uency’; they refer to ‘high fl uency’, which we need to reach in order to read as a leisure pastime, as 160 words per minute. When ‘survival’ reading or ‘spot’ reading, a speed of only approximately 40 words per minute is needed. Whittaker & Lovie-Kitchin have shown that, when we approach our resolution threshold, we practise survival reading. To improve the reading ability and thus increase comfort and satisfaction, print size and/or contrast have to be increased well above those required for survival reading. The increases required have been deemed to be the acuity and contrast reserves (Table 7.4).

Data presented by Whittaker & Lovie-Kitchin31 indicate that, to achieve optimal reading performance, text has to be 6 times larger and 30 times greater in contrast than text presented at threshold size and contrast levels. The patient with low vision hoping to regain reading fl uency, as opposed to optimal performance, must

Table 7.4 Acuity and Contrast Reserves Required for Three Different Reading Tasks

Visual requirement Optimal Highly fl uent Survival

reading reading reading

Reading speed (wpm) 300 160 40

Acuity reserve 6 : 1 3 : 1 1 : 1

Contrast reserve 30 : 1 10 : 1 3 : 1

Field of view (no. of 4–6 4–6 1characters required)

Optimal reading is reading at maximum capacity, highly fl uent reading is reading with ease and comfort whereas survival reading is what is required to tackle just resolvable reading tasks. (wpm, Words per minute.)

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be presented with text that is 3 times larger and 10 times higher in contrast than that detected at threshold. Whereas acuity reserves can be maximised through the provision of optimal low vision aids, contrast reserves, if they are to be maximised, may require specialist lighting or the use of electronic vision enhancement devices.

The impact of target or letter size on reading speed is best illus-trated graphically, where it can be seen that over a very wide range of print sizes the normally sighted pre-presbyopic individual achieves a relatively constant reading speed (Fig. 7.8). Only when print of N4 is being read at a working distance of 40 cm does reading speed begin to drop. Thereafter, performance drops rapidly, word reading becoming impossible at approximately N3 in an eye with a distance acuity equivalent to N2.32

In patients with low vision, the reading speed curve (as on the graph) assessed with a conventional near add moves to the right. Depending on the nature of the pathology, the slope may also be less severe and reading speed, even with large print, may never be optimal. With the introduction of a suitable low vision aid, the curve moves back to the left, but the best possible reading speed may never reach optimal levels because of handling limitations and restricted fi eld size. Furthermore, if used to read large print, the process may be complicated by restriction in the fi elds of view with the result that the right-hand side of the curve begins to rise.

Figure 7.8 Reading speed as infl uenced by print size in an individual with normal vision (A) and a person with age-related macular degeneration (B).

300

100

30

10

0.03 0.1 0.3 1Character size (degrees)

3 10 30

Rea

ding

spe

ed (w

pm)

A = Normal visionB = Low vision

A

B

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7.5.2 Near (reading) acuity charts

Historically, near acuities have been specifi ed in one of three forms: Jaeger, N Point and Snellen equivalent. More recent charts include the Keeler A series and Sloan M series charts, whereas those used in progressive low vision units include the Bailey–Lovie word reading charts, the Pepper reading test charts and the MN read charts (Fig. 7.9). A comparison of acuity values specifi ed in the most common formats is shown in Table 7.5.

Jaeger

Familiar to most older practitioners, the origins of the Jaeger chart were in the printing houses of Vienna. Text is formulated from type of 20 different sizes, the size progressions of which have never been standardised. Many of the charts produced according to the Jaeger system also used highly variable word and letter spacings.33

Snellen equivalent system charts

The scientifi c basis for the Snellen near system is identical to that of the distance acuity system in that each letter has been con-structed such that, when held at a specifi ed distance, it will subtend an angle of 5 minutes of arc at the eye (see Section 7.1 above). Most near vision Snellen charts have been produced as one-seventeenth of the original chart and are designed to be used at 35 cm. The major problem with these charts is that when acuity values are expressed as Snellen equivalents the value holds true only when the chart is used at the specifi ed test distance.

N point system charts

The N point system has been incorporated into the series of charts approved for use in the UK by the Faculty of Ophthalmologists.34

Practical advice

When measuring reading performance, note should be made not only of the threshold visual resolution, but also of the print size at which reading speed starts to slow. Optimisation of task lighting should be performed before prescribing magnifi cation aids so that enlargement can be kept to a minimum.

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A printer’s block is 1/72 of an inch (0.353 mm) for each N point. However, the letters do not extend to the end of the block, so the letters are approximately 1/44 of 1 cm (1/107 of an inch). The height of the lower-case letter ‘h’, as printed in N5 text, is thus 5/107 of an inch. Lower-case letters are smaller again by a factor of approximately 0.68. The typeface used is that designed in 1932 for The Times newspaper (Times roman). Although not easily com-parable with LogMAR-based equivalent near charts, N point charts have the advantage of being familiar to virtually all UK practitioners; a doubling in point size represents a doubling in letter size and, hence, when viewed at an identical distance, a doubling in retinal image size. Point size is also used in computing to specify font dimensions.

Keeler A series charts

Designed to complement the similarly named distance charts (see Section 7.1), letter sizes have been calculated such that letters

Figure 7.9 Selection of near acuity charts including those designed for the assessment of near text reading acuity: a, Maclure reading chart; b, Moorfi elds bar reading chart; c, Peter Rabbit reading chart; d, Sussex near test type chart; e, Bailey–Lovie word reading chart; f, Keeler A series near chart; g, Belfast ARMD reading speed chart; h, Pepper chart.

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151

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152

forming A1 text, when held at a working distance of 25 cm, will subtend 5 minutes of arc at the eye. Successive lines increase in size by a factor of ×1.25 or 0.1 Log units. Designed specifi cally to assist the low vision practitioner with the task of calculating expected magnifi cation requirements, the system was in many ways ahead of its time. The only real disadvantage concerned the layout and spacing of words, which varied considerably from top to bottom.7

Sloan M series charts

Specifi ed in M notation and designed to complement Sloan dis-tance charts (see Section 7.1), the M system was, until recently, used almost universally throughout the USA. The series of fi ve reading cards was designed specifi cally to assist with the calcula-tion of the anticipated reading addition required to achieve any given reading task by patients with low vision. The recommended working distance at which to use these charts is 40 cm.35

Bailey–Lovie word reading charts

Ranging in size from 1.6 to 0.0 LogMAR (N80 to N2, or M10 to M0.25, equivalents), these charts (26 × 20.6 cm) incorporate 17 lines of unrelated words and are designed for use at 25 and 40 cm. There are two words in each of the larger categories, increasing to six as one moves down the chart towards the 0.0 threshold level. The charts are ideal for measuring reading acuity, but are restricted in their ability to assess reading speed. Print sizes are also specifi ed in N point notation.32

Pepper visual skills for reading test (VSRT)

Available in text sizes of N8 to N32 (M1–M4), these charts were designed to test reading speed and fl uency in patients with macular disease. The charts consist of 13 lines of text of identical size. The complexity of the reading task increases as one moves down the page, ranging from well spaced single-letter identifi cation at the top to complex unrelated longer words at the bottom. These charts are designed for use in low vision clinics where patients with reduced reading performance are to be given training exer-cises designed to increase reading speed.36

MN read charts

The Minnesota low vision reading test is available in several forms, all of which are available in both conventional and reverse con-

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trast. The original test was computer based and designed specifi -cally to assess on-screen reading speed using scrolled simple sentences.37 Printed versions, which achieved comparable results when used to assess reading speed, have been produced by Ahn et al.38 The most well known versions have, however, been pro-duced as acuity charts incorporating text ranging in size from 1.3 LogMAR through to −0.2 LogMAR when held at the recom-mended working distance of 40 cm. The reverse contrast facility is particularly useful when testing patients who fi nd refl ected glare from the white page uncomfortable or debilitating.39

PNAC chart

The PNAC (practical near acuity chart) represents an attempt to standardise the number and diffi culty of words on a LogMAR chart and to allow a quick measurement of near visual acuity. It uses related three-, four- and fi ve-letter words on each line. In a comparison with the Bailey–Lovie near chart, which uses unre-lated words, the use of related words was found not to affect the threshold near acuity measured.40 The chart can be read from the top downwards until the person can no longer resolve the words. The print size at which the reading speed slows, as well as the threshold for near vision, should be noted.

7.5.3 Near vision testing strategies

As outlined in Chapter 6, it is imperative to undertake near vision assessment only after having completed an accurate refraction and having determined optimal distance acuities and, where appropri-ate, contrast sensitivity or low contrast acuity measurements. Near (reading) acuities should be recorded through the patient’s exist-ing reading correction and, thereafter, through a +4.00 near addi-tion. In the UK, it is standard low vision practice to increase the strength of the addition in +4.00 steps until the patient can achieve the desired acuity. This can be done using any of the LogMAR-based acuity cards referred to above.

Once reading acuity has been determined monocularly, and under binocular conditions if the objective is to achieve binocular-ity, the process of evaluating reading speed and fl uency using Pepper, MN read cards or in-house equivalents can be commenced. After the assessment and the provision of appropriate low vision aids, non-optical aids and rehabilitation advice, consideration

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should be given to low vision training (see Chs 16–18), which may assist patients to read faster and more fl uently and to utilise their near vision potential, with or without a low vision aid, most effectively.

7.6 Visual fi elds

In a conventional optometric setting (primary care), visual fi elds are generally assessed to detect the presence of early-onset disease (glaucoma). Within a secondary care environment, visual fi elds are more likely to be used to assess progression of the disease. The situation within the low vision clinic is entirely different in that assessment of visual fi elds is undertaken in order to determine the magnitude of loss and, thereafter, to equate functional loss with disability.

The elderly patient who has experienced a stroke and developed a right-sided hemiparesis will thus have visual fi elds assessed to determine the presence and, if detected, the extent of right-sided hemianopic fi eld loss (Fig. 7.10). The presence of fi eld loss and potential neglect will have a profound impact on reading perfor-

Figure 7.10 Humphreys 24/2 monocular fi elds (right and left) illustrating a dense right-sided homonymous hemianopia in a patient with right hemiparesis resulting from a left-sided cerebrovascular accident.

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mance and social awareness. Individuals with retinitis pigmen-tosa will similarly have visual fi elds assessed to correlate loss with the extent of mobility problems experienced by the patient. Those with inferior altitudinal loss may have fi elds quantifi ed in order to help explain mobility restrictions and to illustrate the need for safety strategies. Those with central fi eld loss resulting from macular disease will have characteristic impairments to reading fl uency.

7.6.1 Peripheral visual fi elds

In the authors’ opinion it is unhelpful, and in fact unfair, to assess the visual fi elds of those with profound visual impairment using complex full-fi eld threshold automated perimetry. This process, although providing information that may be useful in the process of rehabilitation, is time consuming and often distressing for the patient (see Fig. 7.10). The resulting fi eld plots, which are charac-terised by ‘blackness’ and ‘loss’, often overestimate the true extent of disability and underestimate the extent of useful vision. Screen-ing programmes, of which there are many, generally run 6–10 dB above threshold and are, on the whole, more useful. Much more useful, however, are data that can be obtained from accurately and carefully performed confrontational visual fi elds assessment or, if available, the results of perimetry performed using a Tangent screen, Goldmann bowl perimeter or Arc perimeter. Crucial to obtaining repeatable and accurate results is the process of ensur-ing stable central fi xation. This can be facilitated through the use of an enlarged ‘cross type’ fi xation target.

7.6.2 Central visual fi elds

Central perimetry, utilising automated perimeters, may be useful in determining the extent of scotoma size and depth in those with macular or parafovial lesions. This can be undertaken using, for example, Humphreys 10/2 type programmes. Alternatively, use of the Amsler chart to determine the subjective quality of the central fi eld and the signifi cance of metamorphopsia may be invaluable. There are, however, concerns regarding the reliability and repeat-ability of the Amsler chart, and patients often fi nd it diffi cult to be specifi c about areas of loss and distortion.41 The development of the scanning laser ophthalmoscope in the early 1990s paved the way for the coupling of central visual fi eld testing and fundus

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observation. Using this new technology, patients with central sco-tomas could be tested longitudinally in the knowledge that fi xa-tion loss could be compensated for, thus enhancing the chances of obtaining accurate and recordable fi elds in patients with macular damage.42 More recently, the development of microperimeters such as the Nidek MP1 have made the technology more affordable and less dependent on technical expertise (Fig. 7.11 [Plate 11]).43

7.6.3 Rehabilitation advice and assistance

Although less can be done to alleviate the problems resulting from fi eld loss than for the problems associated with a reduction in visual acuity, therapeutic options are available. Patients can be instructed in scanning and peripheral viewing techniques and, most importantly, made aware of the need to develop safe viewing strategies (see Ch. 17). Highly motivated patients may, however, benefi t from the prescription of reverse telescopes, Fresnel prisms or clip-on mirrors.

Reverse telescopes, which are generally low powered Galilean telescopes (×2), can be hand held or spectacle mounted. Field expansion is gained at the expense of minifi cation. Fresnel prisms, usually 25Δ to 30Δ in strength, have been used in cases of hemiano-pic fi eld loss. These are mounted on the spectacle frame such that the prism is applied only to the half of the spectacle lens that is in the blind fi eld. As the user glances towards the prism, the viewer is able to see into the non-seeing fi eld. The base of the prism is always placed in the direction of non-seeing fi eld. After adapta-tion, prisms can be fi lled binocularly, although users are often bothered by a combination of aberrations and ‘Jack in the box’ image jump.44 Clip-on mirrors have also been advocated for treat-ing fi eld loss resulting from hemianopia. In these cases, the mirrors, which are usually mounted on the frame of the spectacles, super-impose a reversed image of the picture falling on the non-seeing retina on to the seeing retina. The diffi culty for the user is in dif-ferentiating nasal from temporal images.45

One of the most important aspects of fi eld assessment, associ-ated with low vision, concerns driving. Current UK legislation states that failure constitutes fi eld loss of ‘at least 120° on the hori-zontal measured using a target equivalent to the white Goldmann III4e settings’. In addition, there should be ‘no signifi cant defect in the binocular fi eld which encroaches within 20° of fi xation above or below the horizontal meridian’.46 Many of those with borderline

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B

A

Figure 7.11 (Plate 11) A,B, The Nidek MP1 microperimeter permits the examiner to position targets accurately, and is used to assess retinal sensitivity within, and adjacent to, retinal areas of specifi c interest. (Reproduced with kind permission of Nidek Technologies.)

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fi elds feel perfectly safe when driving, and the prospect of having a licence withdrawn, and the associated loss of independence, may induce distress or even anger. It is essential that practitioners advising on these issues record appropriate advice in the clini-cal records and inform the patient’s general practitioner of the fi ndings.

Bioptic telescopes are spectacle-mounted telescopes that are positioned to allow the user to interchange from viewing through the telescope to viewing through the spectacle lens.47 When the telescope is intended for viewing distant objects, it is usually mounted high in the spectacle lens. Typically the user locates the object of interest while viewing the world directly through the carrier lens. Then, in order to obtain the magnifi ed view through the telescope, the head is tilted forward so that the viewing axis of the telescope is directed towards the object of regard. Bioptic telescopes may be used for viewing objects at near; the telescope is typically mounted low in the spectacle lens and used in a manner similar to that of a bifocal lens. In the USA more than half of the states permit the use of bioptic telescopes for driving, with rules and limitations that vary from one state to another. In Europe, this issue is currently under review.

Practical advice

The purpose of undertaking visual fi eld assessment within the low vision clinic should be to explain the nature of disability described or noted by the patient.

7.7 Colour vision

Optometrists generally equate defective colour vision with geneti-cally determined red/green loss in males (protanopes and deuter-anopes). Colour vision tests such as the Ishihara test are designed specifi cally to differentiate normal from abnormal, and anoma-lous from total. The colours of the targets chosen are such that they lie along dichromatic confusion lines. Colour vision loss asso-ciated with low vision, particularly when it is acquired and chronic, is different; the amount of loss, the extent of the defect and the nature of loss equate primarily with the damage caused to cone photoreceptors and their neural network (Table 7.6). One also has

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to bear in mind that those with low vision may, in addition, have an underlying congenital colour vision defect.

For these reasons, there is little point in using pseudo-isochromatic plate tests to evaluate the nature of colour vision loss in patients with low vision. Research conducted using simulated blur in normal subjects would tend to suggest that conventional test results become unreliable when acuities drop below 6/20 [LogMAR 0.5], and extremely diffi cult when acuities drop below 6/60 [LogMAR 1.0].48 It is generally assumed that colour matching tests, such as the Farnsworth 100 hue and D15 tests, are more appropriate for detecting and differentiating acquired colour vision defi cits. Here, too, size can pose problems, hence the development of the Jumbo D15 and PV16 tests, which can be used by those with acuities as low as 3/60 [LogMAR 1.3] (Fig. 7.12 [Plate 12]).49

As with conventional colour vision testing, all tests should be carried out under standard conditions when illuminated with northern daylight equivalent light sources. Importantly, defects, when detected, should not be classifi ed into the conventional con-genital categories but should instead be categorised according to colour confusion categories (i.e. red/green or blue/yellow). Numer-ous tests for the detection and monitoring of eye disease list the frequently reported confusion pairs associated with various pathologies: cataracts – blue/yellow; cone dystrophy – red/green;

Table 7.6 Classifi cation of Acquired and Hereditary Colour Vision Loss

Hereditary Acquired

Usually male (M : F ratio 10 : 1) Sex equality

Usually red/green Often blue/yellow

Predictable colour confusion Unpredictable colour confusioncharacteristics characteristics

Binocular Monocular and asymmetric

Generally repeatable results Variable test–retest results

Static Often progressive

Often unaware of nature of loss Aware of changing colour perception

Normal visual acuity, contrast Abnormal visual acuity, contrast sensitivity and visual fi elds sensitivity or visual fi elds

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glaucoma – blue/yellow. There are, however, many exceptions to the rule. The often quoted Kollner’s law, that outer retinal larger lesions give rise to blue/yellow type defects whereas inner retinal layer and optic nerve lesions give rise to red/green defects, is also a generalised oversimplifi cation.50

Figure 7.12 (Plate 12) Selection of colour vision tests: a, City colour vision test; b, Ishihara plates; c, Jumbo D15 (PV16) (buttons), which are of particular use when testing patients with a visual acuity of 6/20 [LogMAR 0.5] or less.

Practical advice

In considering the characteristics and impact of defective colour vision in patients with low vision, remember that an acquired defect may be superimposed on a pre-existing congenital colour vision disorder.

As is the case with reduced contrast sensitivity, defective colour vision cannot be cured; however, advice on how to compensate for demonstrable loss can be invaluable, particularly in the educa-tional and employment environments. Research results indicate that patients with low vision exhibit preferences for high contrast colour combinations irrespective of what the actual colours are.50 Colour and luminance contrast should be used to complement each other when advising on rehabilitative issues.

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7.8 Glare sensitivity

Whereas photophobia, in its true sense, occurs as a result of pathol-ogy affecting the trigeminal nerve, glare is the result of excessive brightness within the visual fi eld.51 Glare is defi ned as either ‘dis-comfort’ or ‘disability’ glare, and is associated with asthenopia, headaches and ‘squinting’.

7.8.1 Disability and discomfort glare

Disability glare occurs when individuals, both normally sighted and visually impaired, are subjected to light levels that are higher than those to which they can comfortably adapt. The Chartered Institute of Building Services Engineers (CIBSE) recommenda-tions are that, in order to avoid discomfort glare, the task : surround illumination ratio should not exceed a ratio of 3 : 1.52

Discomfort glare is more prevalent in certain individuals with visual impairment, including those with medial haze (cataract, corneal scarring, etc.) and those with albinism, achromatopsia and aniridia.

Disability glare differs from discomfort glare in that it results in a reduction in retinal resolution. The glare source can result in a diffuse overall increase in retinal illumination, or it can be focal and discrete. When focused, it needs to be close to the line of fi xa-tion for signifi cance to be achieved. The effect can be enhanced in the presence of medial haze and cataract, when it may be referred to as ‘veiling glare’. The disability induced is particularly marked when the targets observed are low contrast in make-up. Disability glare may also occur when the light source involved is seen refl ect-ing off the working surface, in which case it is called ‘refl ective glare’.53

7.8.2 Glare testing

The essence of all glare sensitivity testing is to attempt to quantify the impact that the introduction of a glare source has on vision. In its simplest form, glare sensitivity can be assessed by introduc-ing a glare source, such as a pen torch or light from an anglepoise lamp, into the visual fi eld close to the line of fi xation while the subject under investigation undertakes a visual task.54 Quantifi ca-tion can be achieved if an acuity chart or low contrast letter chart

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is used as the principal target. Correlating the actual reduction in performance with the patient’s subjective comments can prove useful.

The most well known instrument designed specifi cally to assist with the quantifi cation of disability and discomfort glare is the brightness acuity tester (BAT) (Fig. 7.13). With this instrument, the subject views an acuity or low contrast chart through a 12-mm aperture hole in a 60-mm white hemispherical dome, which is held in close proximity to the eye. Acuity measurements can be recorded in the standard way when the rheostat is adjusted to one of three positions (12-, 100- and 400-foot Lamberts). The three settings cor-respond to bright overhead fl uorescent lighting, indirect sunlight on a cloudy day, and direct overhead sunlight.55 Other tests that have also been evaluated as glare disability tests include the Vistech MCI 8000 and the Miller–Nadler glare tester.56

7.8.3 Management of glare

The principal approach to managing glare is to do everything possible to remove the source. If, for example, it is caused by light from a luminare adjacent to, or refl ecting off, the working plane, simply increase the angle of substence between the light source and the eye. Alternatively, one may try to reduce the brightness of the offending source by reducing the bulb strength or using an appropriate diffusing fi lter. If this is impractical or impossible, consideration should be given to fi lter lenses such as the NoIR sun shields, or to peaked caps and typoscope-type devices.

Figure 7.13 The brightness acuity tester (BAT).

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7.9 Summary

In this chapter, we have sought to review methods used to quan-tify the main visual functions, a defi cit of which may impact on levels of visual impairment. Specifi c attention has been paid to measurements of visual acuity and the variety of charts now avail-able to those interested in the measurement of visual resolution. Attention has also been paid to the assessment of near acuity and the importance of assessing reading speed, ability and fl uency. Third, the importance of evaluating performance when undertak-ing low contrast tasks has been determined. Finally, issues sur-rounding the assessment of visual fi elds, colour vision and glare sensitivity in visually impaired patients have been covered.

References

1. Jackson AJ, Bailey IL. Visual acuity. Optometry in Practice 2004; 5:53–70.

2. Snellen H. Test types for determination of the acuities of vision. Offi cial War Offi ce Edition (2nd edn). Utrecht: PW Vander Weijer; 1864.

3. Bennett AG. Ophthalmic test types. British Journal of Physiological Optics 1965; 22:238–271.

4. Bailey IL, Lovie JE. New design principles for visual acuity letter charts. American Journal of Optometry and Physiological Optics 1976; 53:740–745.

5. BSI 4274-1. Visual acuity test types. Part 1: Specifi cation for test charts for clinically determining distance visual acuity. London: British Standards Institution; 1968.

6. BSI 4274-1. Visual acuity types. Part 1 – Test charts for clinical determination of distance visual acuity: specifi cations. London: British Standards Institution; 2003.

7. Keeler CH. Visual aids for the partially sighted. Transactions of the Ophthalmological Societies of the United Kingdom 1956; 76:605–614.

8. Ferris FL, Kassoff A, Bresnick GH, Bailey IL. New visual acuity charts for clinical research. American Journal of Ophthalmology 1982; 94:91–96.

9. Sloan LL. New test charts for the measurement of visual acuity at far and near distances. American Journal of Ophthalmology 1959; 48:807–813.

10. Strong G, Woo GC. A distance visual acuity chart incorporating some new design features. Archives of Ophthalmology 1985; 103:44–46.

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11. Hyvarinen L. Vision evaluation of infants and children. In: Silverstone B, Lang MA, Rosenthal B, Faye EE, eds. The lighthouse handbook on vision impairment and vision rehabilitation, Vol. 2, Ch. 43. New York: Oxford University Press; 2000:799–820.

12. Macnaughton J. Low vision assessment. Edinburgh: Butterworth-Heinemann; 2005.

13. Thompson D. Use and development of computer based test charts in the assessment of vision. In: Doshi S, Harvey W, eds. Investigative techniques and ocular examination, Ch. 2. London: Elsevier; 2003:8–12.

14. Bailey IL. Measurements of visual acuity. Towards standardisation. In: Vision Science Symposium: a tribute to Gordon G Heath. Bloomington: Indiana University; 1988:217–230.

15. Spaeth EB, Fralick FB, Hughes WF, Scheie HG. American Medical Association Council on Industrial Health: special report estimation of loss of visual effi ciency. Archives of Ophthalmology 1955; 54:462–468.

16. Rumney NJ. Using visual thresholds to establish low vision performance. Ophthalmic and Physiological Optics 1995; 15(Suppl 1):S18–S24.

17. Whittaker SG, Lovie-Kitchin JE. The assessment of contrast sensitivity and contrast reserves for reading rehabilitation. In: Kooijman AC, Looijestijn PL, Welling JA, Van Der Widt GJ, eds. Low vision: research and new developments. Amsterdam: IOS Press; 1994:88–92.

18. Campbell FW, Green DG. Optical and retinal factors affecting visual acuity. Journal of Physiology 1965; 181:576–593.

19. Harvey W, Franklin A. Routine eye examination. Edinburgh: Butterworth-Heinemann; 2005.

20. Regan D, Neima D. Low contrast letter charts as a test of visual function. Ophthalmology 1983; 90:1192–1200.

21. Pelli DG, Robson JG, Wilkins AJ. The design of a new letter chart for measuring contrast sensitivity. Clinical Vision Sciences 1988; 2:187–200.

22. Bailey IL. Simplifying contrast sensitivity testing. American Journal of Optometry and Physiological Optics 1982; 59:12.

23. Harvey W, Gilmartin B. Paediatric optometry. Edinburgh: Butterworth-Heinemann; 2004.

24. Eperjesi F, Wolffsohn JS, Bowden J, Napper G, Rubinstein M. Normative contrast sensitivity values for the back-lit Melbourne Edge Test and the effect of visual impairment. Ophthalmic and Physiological Optics 2004; 24:600–606.

25. Hess RF. New and improved contrast sensitivity approaches to low vision. In: Woo GC, ed. Low vision: principles and application. New York: Springer; 1987:1–16.

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26. Arden GB. Testing contrast sensitivity and practice. Clinical Vision Sciences 1988; 2:213–224.

27. Ginsburg AP. A new contrast sensitivity vision test. American Journal of Optometry and Physiological Optics 1984; 61:403–407.

28. Reeves BC, Wood JM, Hill AR. Vistech VCTS 6500 charts – within and between session reliability. Optometry and Vision Science 1971; 68:728–739.

29. Legge G. Glen A Fry Award Lecture (1990): three perspectives on low vision reading. Optometry and Vision Science 1991; 68:763–769.

30. Lovie-Kitchin JE, Bowers AR, Woods RL. Oral and silent reading performance with macular degeneration. Ophthalmic and Physiological Optics 2000; 20:360–370.

31. Whittaker SG, Lovie-Kitchin J. Visual requirements for reading. Optometry and Vision Science 1993; 70:54–65.

32. Bailey IL, Lovie JE. The design and use of a new near vision chart. American Journal of Optometry and Physiological Optics 1980; 57:378–387.

33. Jaeger E. Test types. New York: William Wood; 1868. 34. Law FW. Reading types. British Journal of Ophthalmology 1952;

36:689. 35. Sloan L, Brown DJ. Reading cards for selection of optical aids for

the partially sighted. American Journal of Ophthalmology 1963; 55:1187.

36. Baldasare J, Watson GR, Whittaker SG, Miller-Schaffer H. The development and evaluation of a reading test for low vision individuals with macular loss. Journal of Visual Impairment and Blindness 1986; 80:785–789.

37. Legge GE, Ross JA, Luebker A, LaMay JM. Psychophysics of reading. VIII: The Minnesota Low Vision Reading Test. Optometry and Vision Science 1989; 66:843–853.

38. Ahn SJ, Legge GE, Laebker A. Printed cards for measuring low vision reading speed. Vision Research 1995; 35:1939–1944.

39. Mansfi eld JS, Ahn SJ, Legge GE, Luebker A. A new reading acuity chart for normal and low vision ophthalmic and visual optics/non invasive assessment of the visual system. Technical Digest 1993; 3:232–235.

40. Wolffsohn JS, Cochrane AL. The practical near acuity chart (PNAC) and prediction of visual ability at near. Ophthalmic and Physiological Optics 2000; 20:90–97.

41. Schuchard RA. Validity and interpretation of Amsler grid reports. Archives of Ophthalmology 1993; 111:776–780.

42. Sunness JS, Schuchard RA, Shen N, Rubin GS, Dagnelie G, Haselwood M. Landmark driven fundus perimetry using the scanning laser ophthalmoscope. Investigative Ophthalmology and Visual Science 1995; 36:1863–1874.

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43. Sabates NR. The MP-1 microperimeter. Highlights of Ophthalmology 2005; 33:10–11.

44. Hoppe E, Perlin RR. The effectivity of fresnel prisms for visual fi eld enhancement. Journal of the American Optometric Association 1993; 64:46–56.

45. Goodlaw E. Rehabilitation of the patient with homonymous hemianopia. Journal of Visual Rehabilitation 1993; 7:13–16.

46. DVLA. At-a-glance guide to the current medical standards of fi tness to drive. Swansea: DVLA; 2005. Online. Available: http://www.dvla.gov.uk/at_a_glance/ch6_visual.htm [31 March 2006].

47. Huss C, Corn A. Low vision driving with bioptics: an overview. Journal of Visual Impairment and Blindness 2004; 98:641–653.

48. Miyakawa N, Ichikawa K, Ichikawa H. Studies of methods of testing acquired colour vision defects/the effects of visual acuity. Folia Ophthalmologica Japonica 1984; 35:1597–1603.

49. Collins MJ. Pre age related maculopathy and the desaturated d15 colour vision test. Clinical and Experimental Optometry 1986; 69:223–227.

50. Fischer ML. Clinical implications of colour vision defi ciencies. In: Rosenthal BP, Cole RG, eds. Functional assessment of low vision. St Louis: Mosby; 1996:105–127.

51. Waiss B, Cohen JM. The functional implications of glare and its remediation for persons with low vision. Journal of Visual Impairment and Blindness 1992; 86:28.

52. Chartered Institute of Building Services Engineers. Code for interior lighting (5th edn). London: CIBSE Lighting Division; 1984.

53. Pitts DG. The electromagnetic spectrum. In: Pitts DG, Kleinstein RN, eds. Environmental vision: interactions of the eye, vision, and the environment. Boston: Butterworth-Heinemann; 1993:87–135.

54. Maltzman BA, Horan C, Rengel A. Penlight test for glare disability in cataracts. Ophthalmic Surgery 1988; 19:356–358.

55. Holladay JT, Paryer TC, Trujillo J, Ruiz RS. Brightness acuity test and outdoor visual acuity in cataract patients. Ocular Surgery News 1986; 1:20.

56. Elliott DB, Bullimore MA. Assessing the reliability, discriminative ability and validity of disability glare tests. Investigative Ophthalmology and Visual Science 1993; 34:108–119.

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In Chapter 7 the emphasis was on the assessment of visual function and the impact that damage to the visual system may have on specifi c aspects of visual function. The individual with low vision is, however, unlikely to have much interest in the nature of the biomedical indicators (visual acuity, contrast sensitivity, etc.) that we, as practitioners, use to describe their level of vision. They are interested in whether planned interventions, surgical (in the form of a cataract extraction or photodynamic therapy), optical (in the form of a new spectacle prescription or a low vision aid [LVA]) or rehabilitative (in the form of training or advice), will have an impact on their ability to undertake the tasks of their everyday life. Any evaluation of a healthcare intervention must involve a systematic analysis of outcome, and this must include the patient’s perspec-tive. This process of quality assurance is inherent in clinical audit, which is at the core of current National Health Service reform.1

Whereas the majority of early publications on low vision inter-vention attempted to quantify the success of LVA provision in terms of the improved acuities that could be recorded through the device,2 experienced practitioners routinely incorporated ques-tions on task analysis into their case histories and clinical routines. Not only were the near acuities achievable through a LVA mea-sured, patients were also asked about the duration and regularity of LVA usage, the nature of tasks attempted with LVAs, and han-dling experiences and device limitations.3 The process of analys-ing the nature of the task that the visually impaired person wishes

167

CHAPTER

Assessment of functional visionA. Jonathan Jackson

888

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to undertake, and of evaluating performance with and without the assistance of low vision appliances, is inextricably linked to the successful use of ‘functional vision’. It is improvements in func-tional vision that, in turn, enable the patient to achieve improve-ments in their quality of life.

8.1 Case history and task analysis

Generally speaking, more time and attention have to be given to recording case histories from those with low vision than to record-ing case histories from normally sighted ammetropes. The psycho-logical factors associated with visual impairment are considered in Chapter 5, and some of the issues relevant to refraction are dis-cussed in Chapter 6. The relevance of case histories to the prepara-tion of an integrated rehabilitation plan are, in addition, explored in Chapters 16–19. In this chapter, only those aspects of the case history that relate specifi cally to task analysis are addressed.

What questions should be addressed by the practitioner, or a trained support worker, during the course of a low vision assessment or preclinical interview? The advantage of using preclinical inter-views is that patients will have time to think through the implica-tions of discussion on task analysis before being introduced to a variety of intervention strategies and low vision devices. One of the most well known and formalised task analysis routines is that devel-oped over a 25-year period by staff at the New York Lighthouse.4

The task analysis section of the ‘Lighthouse Low Vision Exami-nation Intake History Form’ includes 43 questions divided into six sections covering travel, distance viewing, daily living activities, near tasks, lighting considerations and job/school-related tasks. Questions are structured in a standard manner: ‘Do you have problems . . .’ and respondents are encouraged to categorise their responses on a four-point scale (not applicable, no problems, mild problems, major problems). They are, in addition, asked to indicate whether each task is, in fact, an objective that the patient would wish to achieve. Questions about travelling concentrate on the problems experienced when travelling alone, locally and in an unfamiliar environment. Questions on distance viewing enquire about diffi culties experienced when climbing stairs, recognising faces and watching television, whereas those on daily living cover issues such as housework, cooking and personal care. Near vision questions, of which there are 11, deal with the classical low vision

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issues of reading print of various sizes, writing, craftwork and colour identifi cation. Questions on lighting cover light and dark adaptation, the use of sunglasses and glare sensitivity. In the employment and education sections, questions focus on diffi cul-ties experienced when undertaking work with instrumentation, computers and technical equipment.

The fi ndings of the task analysis not only inform the practi-tioner about areas where diffi culties are experienced, but enable both practitioner and patient to begin the process of ranking needs objectives. By tackling areas of greatest need fi rst, we are most likely to impact positively on the patient’s quality of life – which is, after all, what we seek to improve.

8.2 Quality of life

The World Health Organization defi nes quality of life as ‘An indi-vidual’s perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns’.5 It also defi nes health as a complete state of ‘physical, mental and social wellbeing’ and not merely as the absence of disease or infi rmity.6 Quality of life is, therefore, infl uenced not only by the nature and magnitude of impairment, but also by the impact this has on a person’s ability to function within a chosen environment. The individual’s attitude to impairment and how they perceive themselves to function within the context of society in general also infl uences their rating of quality of life. Any assessment of quality of life must therefore be broader than task analysis, and include aspects of social, emo-tional and spiritual wellbeing affected by the onset of ill-health and the introduction of treatment.

The development of quality of life (QOL) instruments must be such that measurements quoted are meaningful to the extent that results from different evaluations can be compared. It is this type of information that is of fundamental value to health economists and policy planners. Table 8.1 lists some of the terminology used to describe and explain QOL questionnaires.

QOL instruments are designed according to a standard proce-dure adopted for tests used in psychology and education (Fig. 8.1). This process involves ascertaining the views of patients and healthcare professionals with experience of the topic under con-sideration. Items are grouped into domains, and the results of pilot

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testing, on appropriate samples, are subjected to factor analysis. Modifi ed instruments are then tested for validity (Does it actually measure what it was intended to measure?) in content and con-struct. Thereafter, assessments of ‘discriminal validity’ enable the designers to determine whether the instrument is sensitive enough to divide patient groups into meaningful subgroups. In the case of vision-specifi c instruments, designers often attempt to correlate data recorded within domains to specifi c visual function measure-ments (VA, VF, CS, etc.), although it is generally agreed that subjec-tive QOL instruments provide information in addition to visual function measures and therefore are not expected to be stongly correlated. Instrument designers are also interested in reliability and how this may be affected by systematic bias. Complex statisti-cal analysis is involved in the analysis of test reliability, most instruments having been developed in such a way as to include an index of internal consistency.7

8.3 Generic QOLs

QOLs can be multidimensional instruments, covering many aspects of how poor health may impact on lifestyle, or unidimen-sional, covering only specifi c aspects of lifestyle such as ‘life

Table 8.1 Quality of Life Terminology

QOL instrument A set of questions used to assess daily functioning of health-related quality of life

QOL items Individual questions included in a QOL instrument. Items may be designed to precipitate a dichotomous (yes/no, true/false, agree/disagree) answer or a polytomous (ranking 1–5 or 1–10) answer

QOL domains Subscales within the instrument within which items relate to the same health variable (i.e. general health versus emotional state, or near vision versus distance vision)

QOL bias QOL results may be affected by bias introduced as a result of inappropriate sample selection, in which the study population does not fully represent the population under investigation. Bias may also occur as a result of observer bias, measurement method bias, or as the result of study dropout

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Figure 8.1 Selection of generic vision-specifi c and low vision-specifi c quality of life instruments currently available for use by the low vision practitioner.

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satisfaction’. They may be ‘patient based’, in which patients record their responses to their functional state, or ‘provider based’, in which the clinician makes judgements about the patient’s func-tional state. There are, however, additional instruments designed to record the judgements of family and friends, known as ‘proxy based’ instruments.

One of the most widely used patient-based multidimensional instruments, developed in the USA, is the Sickness Impact Profi le (SIP).8 This is a 12-dimension instrument containing 136 weighted statements relating behaviour to health. The dimensions include ambulation, mobility, body care, social interaction, emotional behav-iour, alertness, communication, work, rest, eating, home manage-ment and recreation. Each dimension is attributed a score level of between 0 (no problem) and 100 (all problems present), and sub-scales can be used to assess both the physical and psychosocial impact of poor health. The instrument, which can be self or inter-viewer administered, takes between 20 and 40 minutes to complete, and an anglicised version is available. In validation studies, the SIP has been found to discriminate between healthy and sick subjects, and it exhibits reasonable agreement with other measures of health. Reliability has been calculated at between 0.94 and 0.97.9

An alternative instrument developed in the UK is the Notting-ham Health Profi le (NHP).10 This instrument, which consists of 38 statements covering six dimensions (energy, pain, emotional reactions, sleep, social isolation and physical mobility), takes only 10 minutes to complete and includes a number of yes/no questions on work, home and social life. Validation studies indicate that cor-relations with other health profi les are fairly high and that repeat-ability correlation coeffi cients are in the order of 0.77–0.88. Concern has been expressed over the scales used in this instrument, as some of them may not be suffi ciently robust to differentiate health change after many interventions.10

The most widely used multipurpose generic health-related QOL instrument is, however, likely to be the 36-question Short Form 36 (SF36) developed by Ware & Sherbourne.11 This was designed for clinical practice with a view to informing policy development. It includes a single multi-item scale assessing eight health concepts (limitations in physical ability; social activity; role limitations caused by physical health; role limitations caused by emotional problems; bodily pain; mental health; vitality; and general health perceptions). It was designed for use on adults by a trained inter-viewer, either in person or by telephone. The instrument has been

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found to be reliable and capable of detecting much lower levels of ill-health than the NHP instrument,12 although it may be less useful when applied to those with profound health problems resulting in hospitalisation.13

Other generic QOL instruments include the Southampton Self Esteem Scale, which measures a person’s sense of purpose, confi -dence and worth,14 the Life Satisfaction Index, which is available in three forms (LSIA 20, LSIA 13 and LSIW 8),15 the Philadelphia Geriatric Centre Morale Scale, which deals with ageing,16 and the Rosser Index of Disability and Distress.17

The problem with generic QOL instruments, when applied to the fi eld of low vision and rehabilitation intervention treatment models, is that they are essentially too coarse to discriminate between treated and untreated groups. Scott et al18 showed this in their evaluation of the impact of low vision service delivery as evaluated by a combination of generic and vision-specifi c QOLs.18

8.4 Vision-specifi c QOL instruments

8.4.1 Vision-specifi c QOL instruments and cataract

One of the fi rst vision-specifi c functional assessment instruments, developed by Bernth-Petersen, was the Visual Function Index (VFI).19 The instrument includes nine items on reading vision, distance vision, television viewing, driving, indoor and outdoor orientation, together with specifi c items on daily living activities including shopping, gardening and personal care. When applied to 123 patients listed for cataract surgery, outcome results were found to correlate fairly well with visual acuity results before and after surgery. Other visual function questionnaires developed with the intention of monitoring changes in vision-specifi c quality of life following cataract surgery are the Lowe’s Visual Function Questionnaire,20 the Activities of Daily Living Scale (ADVS),21 the Assessment of Visual Function Related Quality of Life Question-naire (VFQOL)22 and the Visual Functioning Index (VF14).23

The Lowe questionnaire, which was evaluated by Elliott, con-sists of 14 items grouped into four domains (mobility, near vision, discrimination and quality of vision), and uses a novel disabil-ity index on which patients have to adjust a pointer on a 10-cm ruler to indicate the severity of disability experienced for each item. Results indicated that the near vision domain correlated

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signifi cantly with visual acuity (r = 0.41), whereas mobility, near vision and discrimination all correlated well with contrast sensi-tivity (r = 0.65, r = 0.60 and r = 0.49 respectively).

The ADVS 22-item instrument, developed by Mangione et al,21 utilises fi ve domains (distance vision, near vision, glare disability, nighttime driving and daytime driving) and has a fi ve-point scoring scale, ranging from ‘not diffi cult’ through to ‘stopped doing because of vision’. This instrument has been evaluated extensively, and the overall scores and results for the near vision and night driving subscales have been found to associate strongly with other measures of visual impairment.

The VFQOL instrument, developed by Brenner et al,22 consists of two sections. The fi rst is the Visual Function section, which consists of eight items in three domains (near vision, middle vision and far range vision) and is scored according to a three-point scale. Results correlate well with patients’ self-reported ratings of current overall vision (excellent, good, fair, poor or very poor). The QOL section includes subsections on psychological state, life satisfac-tion and social functioning. In this instrument, life satisfaction is assessed using a Cantril Ladder, on which patients are asked to imagine themselves standing. Those on the top rung of the ten-step ladder consider themselves as having the ‘best possible life’, whereas those on rung one have the worst possible life.24 Correla-tion between the visual function scores recorded over time in patients with age-related macular degeneration showed a positive correlation with QOL domain scores, both diminishing as the disease process worsened. Results from cataract surgery interven-tion cases showed that there was a positive correlation between QOL domain results and visual function scores, as both sets of measures improved after surgery. In conclusion, the magnitude of the average change in QOL domains was proportional to changes in visual function scores.

The VF14 instrument of Steinberg et al23 uses 14 items covering a wide range of activities, including reading medicine labels, ordi-nary newsprint, telephone books, large print and street signs, and face recognition.

8.4.2 Vision-specifi c QOLs and other ophthalmic pathology

Not all vision-specifi c QOL instruments were designed specifi -cally with cataract surgery in mind. The Visual Function after Pan

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Retinal Photocoagulation (VF-PRP) survey, developed by Russell et al,25 is a two-part QOL instrument consisting of 36 items. The fi rst 27 items concentrate on the degree of diffi culty experienced when undertaking daily living activities, including watching tele-vision, driving, moving down steps and general mobility.

The second section of the questionnaire deals with general and emotional health, and with postintervention adjustments. When applied to an ageing population, this instrument showed strong correlations between ageing and diffi culties experienced when reading a wide range of materials from small print to television credits.

Another general vision-specifi c instrument is the Visual Status Inventory (VSI), which was designed for epidemiological studies.26 The initial instrument consisted of 357 items, interviewees being asked to indicate on a fi ve-point scale from ‘never’ through to ‘always’ whether they participated in or undertook a range of visual activities. Domains correlated highly with the instrument score in terms of their ability to identify aspects of visual impair-ment, with sensitivity and specifi city rates for visual acuity, colour vision and binocularity being 90% and 94%, 87% and 99%, and 76% and 78% respectively. Other vision-specifi c QOL instruments developed for use with an ageing population include the Sloan Visual Activities Questionnaire (VAQ)27 and the Visual Perfor-mance Questionnaire (VPQ) of Bergman & Sjostrand.28

8.4.3 NEI-VFQ

Without a doubt the most universally used QOL instrument in the fi eld of ophthalmology and visual science is the National Eye Institute Visual Function Questionnaire (NEI-VFQ).29 This instru-ment was commissioned by the National Eye Institute to be able to assess the impact of a broad spectrum of eye diseases on visual functioning and quality of life. Each of the items within the instru-ment was included as the result of extensive consultation with patient-based focus groups. The focus groups, consisting of patients with a broad range of ocular pathology, concentrated on the symptoms experienced as a result of their condition. The result was a 13-domain instrument (general health, general vision, ocular pain, vision expectations, near vision, distance vision, social prob-lems, mental heath, role problems, dependency, driving, periph-eral vision and colour vision) that exhibited high levels of internal consistency.

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8.5 Low vision QOL instruments

As the prevalence of low vision continues to rise, it becomes more and more important to link reliable outcome measures to low vision rehabilitation programmes in order to secure appropri-ate funding for service delivery and optimise intervention strate-gies. The same rationale that led to the development of QOL instruments specifi cally tailored to cataract surgery,22 panretinal photocoagulation in diabetes25 and the provision of care packages for the elderly28 also applies to low vision where, once again, QOL instruments, if they are to be effective, must be designed specifi -cally with low vision intervention in mind.

8.5.1 Early questionnaires

Many of the early low vision questionnaires that developed out of good clinical practice and the application of ‘needs analysis’ were somewhat arbitrary and never subjected to the scrutiny of valida-tion testing. Nilsson & Nilsson30 utilised a questionnaire approach to evaluate the impact of training and rehabilitation on a popula-tion of patients with low vision due to macular degeneration. McIlwaine et al,31 in one of the fi rst UK-based low vision surveys to look at the cost-effectiveness of service provision, developed a similar approach. The questionnaire approach was also used by Leat et al,32 when evaluating the impact of rehabilitation services established in the highly acclaimed clinical service in Southern Australia. Many ophthalmological QOL questionnaires, although designed with the needs of those with irreversible visual loss in mind (glaucoma,33,34 retinitis pigmentosa,35 cytomegalovirus reti-nitis36 and optic neuritis37), are not valid when applied specifi cally to low vision. Other instruments, such as those developed initially for the cataract surgery service, have been modifi ed for use in a low vision population, but the validity of the modifi cations have not been examined fully.23

8.5.2 Designing a low vision QOL instrument

Any QOL instrument designed specifi cally for use in the low vision arena must include questions that are relevant (relevance) to patients with low vision, and must cover all areas of life affected by low vision (coverage). Questions must not be open (owing to the diffi culty in scoring such items) and the scoring scales must

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be easily understood by those from the population to be assessed. The issues of discrimination, consistency, validity and reliability are exactly the same as those facing all other QOL instrument design teams. Those QOLs that have been through the evaluation process and that, in the opinion of the authors, are appropriate for low vision service evaluation are listed in Table 8.2. A more detailed analysis of these and other vision questionnaires has been pre-sented by de Boer et al.42

8.5.3 The LVQOL

The Low Vision Quality of Life Questionnaire (LVQOL), devel-oped specifi cally for low vision purposes, has four domains (A, Distance Vision, Mobility and Lighting; B, Adjustment; C, Reading and Fine Work; D, Activities of Daily Living) and consists of 25 items. In 24 of the questions, users are asked to respond on a fi ve-point scale (5–1), on which 5 represents no diffi culty and 1 great diffi culty. In the Distance Vision section users are asked, for example, ‘How much of a problem do you have seeing street signs?’, whereas in the Reading and Fine Work section they are asked, ‘With your reading aids/glasses, if used, how much of a problem do you have reading labels (e.g. on medicine bottles)?’ The LVQOL has been shown to be internally consistent, reliable and sensitive to the measure of QOL in those with untreatable

Table 8.2 Qualify of Life Instruments Appropriate for Use in the Evaluation of Low Vision Services

Instrument Reference Characteristics

Activities of Daily Living Mangione et al21 FunctionalScale (ADVS)

Impact of Visual Keeffe et al38 Functional, social andImpairment Profi le (IVIP) psychological

National Eye Institute Mangione et al39 Functional, social,Visual Function psychological andQuestionnaire (NEI-VFQ) physical

Vision Quality of Life Frost et al40 Psychological and socialCore Measure (VCM1)

Low Vision Quality of Life Wolffsohn & Functional, social andQuestionnaire (LVQOL) Cochrane41 psychological

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visual loss. It can be used in the clinical setting without any sig-nifi cant burden on patients or staff (Fig. 8.2).

8.5.4 Administration of QOL instruments

As discussed, QOLs can be administered face to face, by post or telephone. Care needs to be taken when interpreting data collected using different methods of administration. Administration involv-ing human contact (by phone or in person) results in an apparently higher quality of life rating than independent completion (by post). However, each of these methods was consistent over a 3-month period.43 When assessing the impact of service delivery, similar administration methods should be used before and after the inter-vention. Those patients who are most severely visually impaired may struggle to self-administer QOL instruments that need to be read, and they may as a result fail to complete them. However, evidence suggests that they are assisted by friends and relatives, and the completion rate by postal administration is the same as implementation by phone or in person.43 Providing questionnaires for self-completion in a form other than written can be problematic although IT-literate patients may fi nd it appropriate to respond via electronic means. The cost and time saving of postal instrumenta-tion is very attractive, especially in a clinical situation.

Attention also needs to be paid to how results recorded over time may change. Most validated questionnaires have had their reliability tested over relatively short periods,43–45 although care must be taken to ensure that suffi cient time elapses between tests in order that familiarity does not artifi cially increase repeat mea-surements. In assessing the impact of rehabilitation intervention, it is important to evaluate quality of life at baseline (before intervention), immediately after intervention, and at a series of intervals thereafter. Only by so doing can the need for ongoing training be determined. Results from the authors indicate that evaluation is best carried out approximately 2 months after the initial intervention.43

8.6 Summary

The introduction of QOL instruments into the area of low vision is extremely important as, within the ever expanding world of health care, decisions on treatment interventions will be

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Figure 8.2 Low Vision Quality of Life Questionnaire. Users respond on a 5-point scale (5 no diffi culty, 1 great diffi culty). When a task cannot be undertaken because of visual impairment users indicate by circling ‘x’. When a task is of no interest or cannot be undertaken for other reasons the letters ‘n/a’ will be circled. (Redrawn with permission from Wolffsohn & Cochrane 2000.41)

Distance Vision, Mobility and Lighting GradingHow much of a problem do you have: None Moderate Great

With your vision in general 5 4 3 2 1 x n/a

With your eyes getting tired (e.g. only being able

to do a task for a short period of time) 5 4 3 2 1 x n/a

With your vision at night inside the house 5 4 3 2 1 x n/a

Getting the right amount of light to be able to see 5 4 3 2 1 x n/a

With glare (e.g. dazzled by car lights or the sun) 5 4 3 2 1 x n/a

Seeing street signs 5 4 3 2 1 x n/a

Seeing the television (appreciating the pictures) 5 4 3 2 1 x n/a

Seeing moving objects (e.g. cars on the road) 5 4 3 2 1 x n/a

With judging the depth or distance of items

(e.g. reaching for a glass) 5 4 3 2 1 x n/a

Seeing steps or curbs 5 4 3 2 1 x n/a

Getting around outdoors (e.g. on uneven

pavements) because of your vision 5 4 3 2 1 x n/a

Crossing a road with traffic because of your vision 5 4 3 2 1 x n/a

AdjustmentBecause of your vision, are you: No Moderately Greatly

Unhappy at your situation in life 5 4 3 2 1 x n/a

Frustrated at not being able to do certain tasks 5 4 3 2 1 x n/a

Restricted in visiting friends or family 5 4 3 2 1 x n/a

Well Poorly Not explained

How well has your eye condition been

explained to you 5 4 3 2 1 x

Reading and Fine WorkWith your reading aids / glasses, if used, how

much of a problem do you have: None Moderate Great

Reading large print (e.g. newspaper headlines) 5 4 3 2 1 x n/a

Reading newspaper text and books 5 4 3 2 1 x n/a

Reading labels (e.g. on medicine bottles) 5 4 3 2 1 x n/a

Reading your letters and mail 5 4 3 2 1 x n/a

Having problems using tools (e.g. threading a

needle or cutting) 5 4 3 2 1 x n/a

Activities of Daily Living

How much of a problem do you have: None Moderate Great

Finding out the time for yourself 5 4 3 2 1 x n/a

Writing (e.g. cheques or cards) 5 4 3 2 1 x n/a

Reading your own hand writing 5 4 3 2 1 x n/a

With your every day activities (e.g. house-hold chores) 5 4 3 2 1 x n/a

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determined by cost-effectiveness and benefi ts. Measurement of quality of life does not replace functional measures of vision (such as visual acuity and contrast sensitivity), but instead complements them in the assessment of a patient’s visual status.

References

1. Working for Patients 1989 London: HMSO. 2. Fonda GE. Report of fi ve hundred patients examined for low

vision. Archives of Ophthalmology 1956; 56:171–175. 3. Jackson AJ, Silver JH, Archer DB. An evaluation of follow up

systems in two low vision clinics in the United Kingdom. In: Woo GC, ed. Low vision: principles and applications. New York: Springer; 1986:396–417.

4. Rosenthal BP. The function based low vision evaluation. In: Rosenthal BP, Cole RG, eds. Functional assessment of low vision. St Louis: Mosby; 1996:1–25.

5. Parrish RK. Visual impairment, visual functioning and quality of life in patients with glaucoma. Transactions of the American Ophthalmological Society 1996; 19:919–1028.

6. Ellwein LB, Fletcher A, Negrel AD, Thulasiraj RD. Quality of life assessment in blindness prevention interventions. International Ophthalmology 1995; 18:263–268.

7. Massoff RW, Rubin GS. Visual function assessment questionnaires. Survey of Ophthalmology 2001; 45:531–548.

8. Bergner M, Bobbitt RA, Carter WB, Gilson BS. The Sickness Impact Profi le: development and fi nal revision of a health status measurement. Medical Care 1981; 19:787–805.

9. Fletcher AE, Dickinson EJ, Philip I. Audit measures: quality of life instruments for everyday use with elderly patients. Age and Ageing 1992; 21:142–150.

10. Hunt SM, McEwan J, McKenna SP. Measuring health status. Beckenham: Croom Helm.

11. Ware JE Jr, Sherbourne CD. The MOS 36-item short-form health survey (SF36). I. Conceptual framework and item selection. Medical Care 1992; 30:473–483.

12. Brazier JE, Harper R, Jones NMB et al. Validating the SF36 health survey questionnaire: new outcome measure for primary care. British Medical Journal 1992; 305:160–164.

13. Gladman IRF. Assessing health status with the SF36. Age and Ageing 1998; 27:3.

14. Coleman P. Assessing self-esteem and its sources in elderly people. Ageing and Society 1984; 4:117–137.

15. Neugarten BL, Havig Hurst RJ, Tubin SS. The measurement of life satisfaction. Journal of Gerontology 1961; 16:134–143.

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16. Powell-Lawton M. The Philadelphia Geriatric Centre Morale Scale: a revision. Journal of Gerontology 1975; 30:85–89.

17. Rosser R, Kind P. A scale of valuations of states of illness: is there a social consensus? International Journal of Epidemiology 1978; 7:347–358.

18. Scott IU, Smiddy WE, Schiffman J, Fuer WJ, Pappas CJ. Quality of life of low-vision patients and the impact of low-vision services. American Journal of Ophthalmology 1999; 128:54–62.

19. Bernth-Petersen P. Visual functioning in cataract patients: methods of measuring and results. Acta Ophthalmologica (Copenhagen) 1981; 59:198–205.

20. Elliot DB, Hurst MA, Eatherill J. Comparing clinical tests of visual function in cataract with the patients’ perceived visual disability. Eye 1990; 4:712–717.

21. Mangione CM, Phillips RS, Seddon JM et al. Development of the activities of daily living scale – a measure of visual function status. Medical Care 1992; 30:1111–1126.

22. Brenner MH, Curbow B, Javitt JC et al. Vision change and quality of life in the elderly: response to cataract surgery and treatment of other chronic ocular conditions. Archives of Ophthalmology 1993; 111:680–685.

23. Steinberg EP, Tielsch JM, Schein OD et al. The VF14: An index of functional impairment in patients with cataract. Archives of Ophthalmology 1994; 112:630–638.

24. Cantril H. The pattern of human concerns. New Brunswick, NJ: Rutgers, University Press; 1965.

25. Russell PW, Sekuler R, Fetkenhour C. Visual function after pan retinal photocoagulation: a survey. Diabetes Care 1985; 8:57–63.

26. Coren S, Hakstian R. Visual screening without the use of technical equipment: preliminary development of a behaviourally validated questionnaire. Applied Optics 1987; 26:1468–1472.

27. Sloane M, Ball K, Owsley C, Bruni JR, Roenker DL. The Visual Activities Questionnaire: developing an instrument for assessing problems in everyday visual tasks. Technical Digest, Noninvasive Assessment of the Visual System, Topical Meeting of the Optical Society of America 1992; 1:26–29.

28. Bergman B, Sjostrand J. Vision and visual disability in the daily life of a representative population sampled age 82 years. Acta Ophthalmologica (Copenhagen) 1992; 70:33–43.

29. Ellwein LB. Quality of life outcome measures. In: Massof RW, Lidoff L, eds. Issues in low vision rehabilitation: service delivery, policy and funding. New York: AFB Press 2001:P143–P158.

30. Nilsson UL, Nilsson S-EG. rehabilitation of the visually handicapped with advanced macular degeneration. Documenta Ophthalmologica 1986; 62:345–367.

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31. McIlwaine GG, Bell JA, Dutton GN. Low vision aids – is our service cost effective? Eye 1991; 5:607–611.

32. Leat SJ, Fryer A, Rumney NJ. Outcome of low vision aid provision: the effectiveness of a low vision clinic. Optometry and Vision Science 1994; 71:199–206.

33. Ross JE, Bron AJ, Clarke DD. Contrast sensitivity and visual disability in chronic simple glaucoma. British Journal of Ophthalmology 1984; 68:821–827.

34. Parrish RK. Visual impairment, visual functioning and quality of life assessments in patients with glaucoma. Transactions of the American Ophthalmological Society 1996; 19:919–1028.

35. Lowe J, Drasdo N. Patients’ responses to retinitis pigmentosa. Optomety and Vision Science 1992; 69:182–185.

36. Wu AW, Coleson LC, Holbrook J, Jabs DA. Measuring visual function and quality of life in patients with cytomegalovirus retinits: development of a questionnaire. Archives of Ophthalmology 1996; 114:841–847.

37. Cleary PA, Beck RW, Bourque LB, Backlund JC, Miskala PH. Visual symptoms after optic neuritis: results from the optic neuritis treatment trial. Journal of Neuro-ophthalmology 1997; 17:18–28.

38. Keeffe JE, McCarty CA, Hassell JB, Gilbert AG. Description and measurement of handicap caused by vision impairment. Australian and New Zealand Journal of Ophthalmology 1999; 27:184–186.

39. Mangione CM, Lee PP, Pitts J et al. Psychometric properties of the National Eye Institute Visual Function Questionnaire (NEI-VFQ). Archives of Ophthalmology 1998; 116:1496–1504.

40. Frost NA, Sparrow JM, Durant JS, Donovan JL, Peters TL, Brookes ST. Development of a questionnaire for measurement of vision related quality of life. Ophthalmic Epidemiology 1998; 5:185–210.

41. Wolffsohn JS, Cochrane AL. Design of the low vision quality-of-life questionnaire (LVQOL) and measuring the outcome of low vision rehabilitation. American Journal of Ophthalmology 2000; 130:793–802.

42. de Boer MR, Moll AC, de Vet HCW, Terwee CB, Volker-Dieben HJM, van Rens GHMB. Psychometric properties of vision-related quality of life questionnaires: a systematic review. Ophthalmic and Physiological Optics 2004; 24:257–273.

43. Wolffsohn JS, Cochrane AL, Watt NA. Implementation methods for vision-related quality-of-life questionnaires. British Journal of Ophthalmology 2000; 84:1035–1040.

44. Harper R, Doorduyn K, Reeves B et al. Evaluating the outcomes of low vision rehabilitation. Ophthalmic and Physiological Optics 1999; 19:3–11.

45. Bullimore MA, Raasch TV, Cutter GC et al. Quality of life assessment in a low vision population. Investigative Ophthalmology and Visual Science 1997; 38:S710.

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CHAPTER

9.1 Introduction

This text is intended to provide the practitioner with pertinent and practical information on low vision that will, in turn, enable them to provide their visually impaired patients with the advice and/or devices they need. Fundamental to using the hardware of low vision – low vision aids (LVAs) – is an understanding of the con-cepts of magnifi cation, as applied to real patients, using actual LVAs to undertake real-world tasks. Many of the prosaic and mathematical approaches to low vision magnifi cation are in fact confusing and overly complicated for the practical situation. Even when simplifi ed, the assumptions made in many magnifi cation calculations can cause the unwary to derive unpredictable results. This is one reason why many optometrists never become involved in the provision of low vision services. This chapter aims to demys-tify the optics of low vision.

SECTION THREE

Low vision hardwareSection Editor: James S. Wolffsohn

Magnifi cationNicholas J. Rumney

999

183

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The interested practitioner will fi nd additional detail on the derivations and arguments pertaining to the more theoretical aspects of magnifi cation in Dickinson.1

9.2 Background knowledge

A practitioner involved in prescribing low vision hardware must have a working knowledge and understanding of:

• Those aspects of the LVA that are invariant and not dependent on the manner in which it is being used

• The predicted increase in resolution due to the enlargement of the retinal image when the LVA is used in a variety of ways

• The available fi eld of view to the patient with any given confi guration.

With this information the likely improvements in vision that can be achieved through the use of LVAs can be determined, and situations in which improvements cannot be obtained can be understood.

9.3 Current concepts

Throughout this text the term magnifi cation, as a property of LVAs, is used only in reference to the ‘trade magnifi cation’ quoted by the manufacturers. In terms of the requirements of the patient, the term used to depict any increase in the resolution capacity of the visual system is described as ‘enlargement’ or the ‘enlargement ratio’ (ER). This is explained in terms of ‘equivalent viewing dis-tance’ (EVD) or ‘equivalent viewing power’ (EVP). This is because the magnifi cation of any given LVA varies depending on how magnifi cation has been calculated.2 The term is amongst the most misunderstood of terms used in low vision practice. Most particu-larly, assumptions pertaining to magnifi cation are fl awed unless detail is provided as to the precise manner in which the LVA is to be used. For example, the term ‘trade magnifi cation’, when applied to a hand magnifi er, quoted by some manufacturers and sup-ported by British Standards Specifi cation, is dependent on the device being held in contact with the patient’s eye (or alternatively their ametropic correction) whilst the patient simultaneously exerts +4.00D of accommodation. This artifi cial situation so rarely

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9Magnifi cation 99

185

arises that the use of such terminology is entirely unhelpful to the practitioner.

In addition, fundamental to any retinal image enlargement is a comparison with the retinal image formed when viewing an object without the assistance of the LVA. It is reasonable to compare the patient’s improvement in resolution achieved with a LVA with that achieved with +4.00D of accommodation or a +4.00DS reading add, and a working distance of 25 cm, if indeed that is how the person normally attempts the task. However, many patients with low vision attend with lower-powered additions (e.g. +3.00DS), whereas younger patients and children use increased levels of accommodation and much shorter working distances (e.g. 10–20 cm), making such comparisons spurious and misleading. It is not necessary to determine actual retinal image size – merely the change in relative image size with magnifi cation.

9.4 Defi nitions

This chapter concentrates on image enlargement, although in certain circumstances the practitioner may seek to diminish the size of an image.

Four different ways of enlarging an image are used in low vision practice (Fig. 9.1):

• Relative distance enlargement• Relative size enlargement• Electronic (transverse) enlargement• Angular enlargement.

If any two are used together (for instance, using a hand magnifi er to read a large-print bank statement), the total magnifi cation is the product of the two.

9.4.1 Relative distance enlargement

This is the enlargement that results from a reduction in the object viewing distance. To specify, it must be referenced to a particular distance (usually 25 cm), although for practical purposes it should be referenced to the habitual working distance used by the patient. The result of reducing the object viewing distance is to increase the angular subtence of the object at the pupil entrance (Figs 9.1 & 9.2 [Plates 13 & 14]). Thus, an object observed at an initial reference

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working distance of 40 cm produces a retinal image twice as large as the original when viewed at a new working distance of 20 cm. If the patient cannot accommodate by the additional +2.50DS needed to maintain focus at the 20-cm working distance, a reading addition is required. This is the principle behind hand and stand

Figure 9.1 Schematic representation of the different methods for achieving retinal image enlargement. A, Unmagnifi ed object; B, decreasing the viewing distance; C, increasing the object size; D, electronic enlargement; E, increasing the angular subtense. (Redrawn with permission from Dickinson 1998.3)

θ´

θ´

NE

NE

NE

h1´

h2´

h3´

h4´

h5´

d1

h1

h2

h1

h4

h1

h1

NE

d1

d3

d1

d1

A

B

C

D

E

θ

θ´

θ´

θ´

θ´

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9Magnifi cation 99

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A

BFigure 9.2 (Plates 13 & 14) Television viewing at 2 m (A), resulting in a doubling of size compared with viewing at 4 m (B). In this case the change in accommodative demand (0.5D for 2-m viewing and 0.25D for 4-m viewing) is likely to be within the patient’s depth of focus (tolerance to blur), and hence a distance prescription is still appropriate.

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magnifi ers (see Chs 10 and 11) and all spectacle-mounted magnifi ers, from the high-powered near addition to hyperocular (see Ch. 12). Enlargement is equal to only F/4 if the initial refer-ence working distance is 25 cm; it would be F/3 if the initial reference working distance were 33 cm (with a +3.00DS addition) (Fig. 9.3).

Practical application of relative distance enlargement shows that not all patients have a linear increase between object distance and visual acuity. Prediction of required enlargement from knowl-edge of the patient’s distance or near visual acuity and the visual demand of the task works relatively well. However, this can also be achieved by increasing the near powered addition in +4.00D steps over the distance prescription, a technique that simultane-ously demonstrates the effect of stronger reading glasses and identifi es patients in whom the benefi ts of optical enlargement are limited (Fig. 9.4).4

Figure 9.3 Schematic representation of the effect of initial reference working distance on the calculated enlargement.

Initial reference workingdistance 25 cm, thereforeenlargement = F/4

In this case, if working distancereduced to 8 cm,enlargement = F/3 = 12/3 = 4x

D

C

B

A

However, if initialreference working distance 33 cm,then enlargement = F/3

If working distance reduced to 8 cm(for example with a +12D nearreading addition),enlargement = F/4 = 12/4 = 3x

25 cm

8 cm

33 cm

8 cm

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Figure 9.4 Schematic representation of a technique for calculating the required near enlargement for a patient (optimally visually corrected for distance viewing) to perform a desired task, simultaneously demonstrating the effect of ‘stronger reading glasses’ and identifying whether optical enlargement is of limited benefi t. If the required ‘comfortable’ near visual acuity is N6, LVAs with an equivalent viewing power of 16.00D (4×) should be tried fi rst. If the patient reads comfortably with the LVA, a lower powered option should be tried as this will increase the fi eld of view and working distance. Conversely, if the patient struggles to read comfortably with the LVA, a higher powered option should be tried in case more enlargement is needed to perform the task.

4.00D N32 at 25 cm

N16 at 12.5 cm

N8 at 8.3 cm

N5 at 6.3 cm

N4 at 5 cm(Practical limit to nearpowered lens addition)

8.00D

12.00D

16.00D

20.00D

25.0 cm

12.5 cm

8.3 cm

6.3 cm

5.0 cm

Near Visual Acuity

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Accommodation: a special case of relative distance enlargement

If a person is pre-presbyopic, they can exert accommodation; most visually impaired children do this naturally in order to achieve improvements in near vision. However, successful and prolonged use of accommodation is dependent on the amplitude of accom-modation available. An accommodative demand close to the per-son’s amplitude of accommodation may result in the need for a reading addition much earlier in life than would be predicted on the basis of normal presbyopic change alone. The reading addi-tions prescribed in these cases are often in the order of +6.00 or +8.00D. The relevance of the exponential decay of accommodation with age cannot be overestimated in this regard, and the optome-trist prescribing reading additions for visually impaired children or young adults should aim to give an add that accounts for at least half to two-thirds of the accommodative demand required when the object is placed at the person’s habitual working distance (Fig. 9.5). It is often just as a child is leaving school, having maintained acceptable near vision levels, thanks to good accommodation reserves, that incipient premature presbyopia sets in. This can all too quickly be forgotten by the optometrist, who fails to prescribe

Figure 9.5 Average decay in accommodation with age showing minimum working distance with maximal effort, and that which should be achievable for sustained near tasks without near correction. (Redrawn with permission from Bennett & Rabbetts 1998.5)

00 10 20 30 40

Age in years

50 60 70 80

10

20

30

40

50

60

70

802.0

InchesMetres

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

One-halfamplitude

Fullamplitude

Shor

test

focu

sing

dis

tanc

e

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a near correction that will compensate for the accommodative demand of the reduced habitual working distance, on the grounds that near acuity was recorded at a single moment in time. Reading text is, by its very nature, a prolonged task that requires sustained accommodative demand.

9.4.2 Relative size enlargement

This is the magnifi cation achieved by increasing the size of the object while the working distance remains the same (see Fig. 9.1). An example of this is the large print book (Fig. 9.6). The enlarge-ment ratio is the comparison between the standard text size (e.g. bank statement in 12-point type) compared with the enlarged version (e.g. 24 point). Measurement is by direct scale comparison which, in the above case, is 24/12 = 2×.

If the use of large print text is combined with a closer working distance, the overall enlargement ratio is the product of the two; for example, 24-point print read at 20 cm compared with 12-point

Figure 9.6 Large print dictionary, diary and newspaper.

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print at 33 cm provides an enlargement ratio of relative size mag-nifi cation (24/12 = 2) multiplied by relative distance magnifi cation (33/20 = 1.6); i.e. 2× 1.6 = 3.2×. The retinal image size produced by the combination of large print held at a reduced working distance is therefore increased by a factor of 3.2. There is much controversy regarding the provision of this form of enlargement for children compared with other methods, as not all tasks can be easily enlarged and much of what a child reads (particularly outside an educational setting) is not available in large print. It has also been shown that reading speed and ability are limited in children using large print compared with those in children using optical aids and normal print.6,7

9.4.3 Electronic (transverse) enlargement

Enlargement is achieved by projecting or electronically changing an image so that the new image has an increased angular subtence at the eye (see Fig. 9.1). The electronic vision enhancement system (EVES), often referred to as a CCTV (closed-circuit television), provides this form of enlargement (see Ch. 14). Enlargement of the image is measured directly by dividing the image height measured from the screen by the original object height. If the image of a 1-cm object produced on the screen measures 9 cm, the enlargement is 9×. This form of enlargement usually allows longer working distances to be utilised. If, for example, the person habitu-ally uses a working distance of 10 cm, but use of the EVES increases the working distance to 30 cm, the overall enlargement is reduced by a factor of 3 (proximal enlargement). Applied to the above case, the enlargement is thus 9/3 = 3×. This may seem paltry in relation to the cost and complexity of the EVES; however, a better posture enables a much longer duration of comfortable use. In addition, unlike most optical forms of magnifi cation, EVES magnifi cation can be ‘zoomed’ over a wide range of enlargements, making the technology very versatile. This is particularly benefi cial when dealing with patients with progressive disease or transient visual loss. Contrast can also be adjusted to individual preferences (see Ch. 14).

9.4.4 Angular enlargement

This is the ratio of the angle subtended by the image through the optical system to the angle subtended by the object when viewed

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directly (see Fig. 9.1). The result is actually no different to the effect achieved using the other types of enlargement already described. However, in this case the vergence of light may be unchanged. Therefore, this is the most effective way to achieve image magnifi -cation at long (up to infi nity) distances. Angular magnifi cation is produced by telescopic LVAs (see Ch. 13), although, when used for near vision tasks, the angular effect is combined with relative dis-tance enlargement (by using a plus lens powered addition ‘cap’).

9.5 Equivalent viewing power (EVP)

This is a concept introduced by Ian Bailey as a logical progression from his consideration of the logarithmic scaling of acuity mea-surements. Bailey, along with others, has pointed out the futility of trying to produce a universal formula and defi nition for mag-nifi cation.8,9 This is because magnifi cation is not an invariant physical property of a lens, but depends on how it is used. Thus, any simplifying assumptions are generally violated as often as they are justifi ed. However, the EVP (in dioptres) of an optical system is a relevant concept, because it can be simply calculated or measured from the components that make it up. EVP applies under whichever circumstances magnifi cation is produced, and is in a notation understood by all eye care practitioners (the dioptre). In practical terms the use of EVP requires only the assumption that the optical system in use is directly equivalent to a single thin lens of power Fe, where the object under view is positioned at the anterior focal point of the thin lens such that the vergence between the eye and lens is zero. The single lens can be thought of as a reading addition worn by an emmetrope, or corrected ametrope, and a comparison, from the point of view of image enlargement, can be made with any other optical system of given EVP.

9.5.1 Calculating enlargement using EVP

EVP can be used in the derivation of enlargement in all practical situations. For example, a presbyopic patient whose reading correction enables him or her to read optimally at 33 cm (using a +3.00D add) will get an enlargement (or an increase in resolv-ing power) of Fe/3 from any magnifying system of equivalent power Fe.

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9.6 Equivalent viewing distance (EVD)

The reciprocal of the EVP yields a measure of the equivalent viewing distance (EVD); that is, an optical system of equivalent power of +20.00D is equivalent to viewing an object at 5 cm. If the reference viewing distance is 25 cm, the improvement in resolu-tion is 25/5 (5× enlargement); if the reference is 40 cm, the increase is 40/5 (8×). Note that these ratios work exactly the same whether the measures used are distance (EVD) or power (EVP).

Approaching from the opposite direction, the reciprocal of viewing distance allows for the derivation of the equivalent power, even for non-optical systems or combinations thereof. For example, a presbyopic patient wearing a +2.00 near addition using an EVES at an enlargement setting of 5× (the on-screen image is fi ve times larger than the object), viewed at 50 cm, will achieve total enlarge-ment of 2.5× compared to a reference distance of 25 cm.

Total enlargement = (EVES enlargement) × (plus lens enlargement) = 5 × (Fe/4) = 5 × (2/4) = 2.5×

If the same increase in resolution over the reference distance was to be achieved using only a simple plus lens, a lens with an equiva-lent power of +10.00DS would be needed (2.5× = +10.00/4), giving an EVD of 10 cm. The person using the EVES is experiencing the same magnifi cation as they would when viewing the original object at a working distance of 10 cm.

9.7 Quantifying enlargement

EVP and EVD can be used to quantify differences between magni-fi er enlargement. For example, if the initial working distance is 25 cm and the resultant equivalent power with one LVA is +8.00DS (EVP = 1/8 = 0.125 m) and another is +12.00DS (EVP = 1/12 = 0.0825 m), then the relative enlargement provided by each will be (0.25/0.125) = 2× and (0.25/0.0825) = 3× respectively. A person reading N24 size text at 25 cm may be expected to be able to resolve N12 and N8 respectively.

Figure 9.7 summarises the usefulness of this concept by illus-trating four different optical or non-optical systems (or combina-tions thereof), all with the same equivalent power but greatly

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Figure 9.7 A, A 4× telescope with +6.00D reading cap (reading distance 16.7 cm). B, A 6× telescope with +4.00D reading cap (reading distance 25.0 cm). C, An 8× telescope with +3.00D reading cap (reading distance 33.3 cm). D, A +24.00D hand magnifi er (reading distance 4.2 cm). Each of these enlargement options has the same equivalent power, but they focus optimally at different working distances. (Redrawn with permission from Fannin & Grosvenor 1996.10)

+6.00D reading cap

4 x TelescopeA

B

C

D

16.67 cm

+4.00D reading cap

25 cm

+3.00D reading cap

+24.00D

33.3 cm

4.17 cm

6 x Telescope

8 x Telescope

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varying confi gurations dependent on need. An assessment concept can be suggested in that one might fi nd the gains in EVP needed for a specifi c gain in resolution and then investigate ways in which different working arrangements may satisfy the needs of the patient. For example, a person who can achieve N48 with their +3.00DS addition bifocal may write using bold large (N24) print with a +6.00DS addition, read necessary tasks (of size N6) with an EVES screen at 33 cm displaying 8× enlargement and shop using a +24.00DS pocket magnifi er (N6).

It should be remembered that being able to resolve detail is not the same as being able to read comfortably. Whittaker & Lovie-Kitchin11 have shown that greater enlargement (suffi cient to leave some acuity in ‘reserve’) is needed for fl uent reading tasks (such as newspapers) compared with simple ‘survival’ reading tasks such as price labels. For example, if a patient wishes to read a newspaper column and the near acuity required to resolve the letters at their print contrast is N8, suffi cient enlargement to allow the patient to resolve approximately N5 size print is required for them to be able to comfortably read the newspaper column. A standard acuity reserve of 0.3 LogMAR has been shown to be appropriate to maximise reading speed.12

9.8 Summary

• There are four different ways of enlarging an image: relative distance, relative size, electronic and angular.

• Enlargement is usually referenced to a distance of 25 cm.• Equivalent viewing power, or its reciprocal equivalent

viewing distance, applies to an optical system under whatever circumstances enlargement is produced.

9.8.1 Practical pearls

• Make a list or mark yout LVAs up with their true dioptric component power if this is not already clear from the manufacturers’ markings.

• Ascertain patients’ acuity requirement(s) when prescribing LVAs.

• Greater enlargement than is predicted by visual acuity is required for fl uent comfortable reading rather than spot or survival reading.

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References

1. Dickinson CM. Optical aids for low vision. In: Charman WN, ed. Vision and visual dysfunction, Vol. 1. London: Macmillan; 1991:183–228.

2. Woo GC, Mah-Leung A. The term magnifi cation. Clinical and Experimental Optometry 2001; 84:113–119.

3. Dickinson C. Low vision: principles and practice. Oxford: Butterworth-Heinemann.

4. Wolffsohn JS, Eperjesi F. The effect of relative distance enlargement on visual acuity in the visually impaired. Clinical and Experimental Optometry 2005; 88:97–102.

5. Bennett AG, Rabbetts RB, eds. Clinical visual optics. Oxford: Butterworth-Heinemann; 1998.

6. Corn A, Ryser G. Access to print for students with low vision. Journal of Visual Impairment and Blindness 1989; 83:340–349.

7. Koenig AJ, Layton CA, Ross DB. The relative effectiveness of reading in large print and with low vision devices for students with low vision. Journal of Visual Impairment and Blindness 1992; 86:48–52.

8. Bullimore MA, Bailey IL. Stand magnifi ers: an evaluation of new optical aids from COIL. American Journal of Optometry and Physiological Optics 1989; 66:766–773.

9. Johnston AW. Understanding how simple magnifi ers provide image enhancement. Clinical and Experimental Optometry 2005; 86:403–408.

10. Fannin TE, Grosvenor T. Clinical optics (2nd edn). Boston: Butterworth-Heinemann; 1996.

11. Whittaker SG, Lovie-Kitchin JE. Visual requirements for reading. Optometry and Visual Science 1993; 70:54–65.

12. Cheong AC, Lovie-Kitchin JE, Bowers AR. Determining magnifi cation for reading with low vision. Clinical and Experimental Optometry 2002; 85:229–237.

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10.1 Advantages and disadvantages

The hand magnifi er is the most familiar of all low vision aids (LVAs) (Fig. 10.1). A hand magnifi er is frequently obtained by the patient before professional help is sought. Unfortunately, LVAs available over the counter are usually of inferior optical quality (rarely aspheric, for example) and are of low power. Those that have an internally illuminated facility often have an unevenly illuminated fi eld of view, and lighting levels are prone to fl uctuate. These magnifi ers are generally suitable only when small amounts of image enlargement are required, and users are often unaware of how they should be used to optimal effect.

Hand magnifi ers are also frequently improperly understood by practitioners because they do not seem to provide the stated mag-nifi cation, and patients complain that higher powered aids are harder to use and provide poorer performance.

There are two main reasons why this is so. The fi rst is the insis-tence by manufacturers and standards authorities that an LVA be specifi ed in terms of units of magnifi cation rather than the dioptric equivalent power of the lens (not to be confused with equivalent viewing power). The second reason is that equivalent viewing power is a combination of the hand magnifi er’s dioptric power, working distance and accommodation/spectacle reading addition, which may be dramatically less than the dioptric equivalent power of the hand magnifi er itself.

198

CHAPTER

Hand magnifi ersNicholas J. Rumney

101010

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One should never lose sight of the fact that hand magnifi ers are amongst the most versatile and useful LVAs available to patients and practitioners. Their advantages do, in many circumstances, outweigh their disadvantages (Table 10.1).

Figure 10.1 A range of hand magnifi ers.

Table 10.1 Advantages and Disadvantages of Hand Magnifi ers

Advantages Disadvantages

Convenient Too easily purchased and used inappropriatelyDiscrete

Socially acceptable Familiarity brings assumption of ease of useGenerally inexpensive

Lightweight Plastic lenses require careful handling andEasy to clean cleaning

Internal illumination Internal illumination increases weight andpossible complexity

Can be used at any Long working distances reduce the distance from the eye enlargement effect when the hand magnifi er is used with near powered lens additions

Lower powers available Require a steady hand and ability to maintain in larger diameters a fi xed working distance, particularly with higher powered devices

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10.2 Practical optics

Higher powered hand magnifi ers (above +6.00DS) cannot be regarded as thin lenses as there are frequently differences between front vertex power (FVP), back vertex power (BVP) and equivalent power of the hand magnifi er (Fm) (F is power and f is distance (focal length)):

• With a plano-convex hand magnifi er, Fe is closest to the FVP, but BVP is greater and is therefore often quoted by manufacturers (Fig. 10.2)

• In a bi-convex lens of equal surface powers, BVP and FVP are equal but Fm is slightly less because the principal planes are inside the lens (Fig. 10.3).

Figure 10.2 Plano-convex hand magnifi er. fFVP, front vertex power; fBVP, back vertex focal length (BVP); fe, focal length from the principal plane P; fe′, focal length from the principal plane P′.

Figure 10.3 Bi-convex hand magnifi er. fFVP, front vertex power; fBVP, back vertex focal length (BVP); fe, focal length from the principal plane P; fe′, focal length from the principal plane P′.

P P´

fFVP

fBVP

fe´

fe

P P´

fFVP

fe

fBVP

fe´

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Patients may use hand magnifi ers with their reading glasses or when accommodating; this results in a two-element optical system separated by (z) cm. The Fe of this new system may be less than the sum of the powers of the individual elements (Fig. 10.4). The formula is:

Fe = Fm + Fa − z · FmFa

where Fe is the equivalent power of the system, Fm is the equivalent power of the hand magnifi er, Fa is the power of add/accommoda-tion, and z is the eye-to-hand magnifi er distance.

Although taught in optics courses, this formula is rarely remem-bered as having any practical use. An understanding of the impli-cations of this formula is essential to the practitioner working with LVAs.

Figure 10.4 Complex lens system of the patient’s reading addition/accommodation and a hand magnifi er.

Practical advice

Remember the thick lens formula, as this enables calculation of dioptric equivalent powers for any LVA and/or spectacle add combination.1

Fa

z

fm

Fm

Object plane

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10.2.1 The special case: when Fe equals Fm

If the eye–magnifi er separation is exactly the same as the focal length, then z is equal to fm. On applying the formula:

Fe = Fm + Fa − z · FmFa,

thus

Fe = Fm + Fa − fm · FmFa

and as fm · Fm is unity (1)

Fe = Fm + Fa − Fa

and so Fe = Fm.Thus, when a hand magnifi er (Fm) is held at its focal length from

the eye, the equivalent power (Fe) of the optical system is exactly the same as that of the hand magnifi er (Fm), irrespective of the presence of any reading addition. The hand magnifi er-to-object distance will be less than the focal length for cases when a reading addition (or accommodation) is used. It will be adjusted so that the image vergence (L′) matches the vergence of the reading addi-tion (the working distance of the addition matches the image posi-tion of the hand magnifi er).

Practical example

A 20.00D hand magnifi er (Fm = 20.00D, fm = 5 cm), used by a presbyopic patient with a +2.50D addition. If the hand magnifi er is placed 5 cm from the front of spectacle lens:


Fe = +20.00 + 2.50 − (0.05 × 20.00 × 2.50)

Fe = +22.50 − 2.50

Fe = +20.00D

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10.2.2 When used by an emmetrope (or corrected ametrope)

When the hand magnifi er-to-object distance is the focal length of the lens, the emerging light bundle has zero vergence (the lens is collimated). In this situation (Fig. 10.5) the light rays incident on the eye are parallel regardless of the distance from the eye to the lens (a Badal optical system).

When an object is in the primary focal plane of the hand magni-fi er the retinal image size is constant, regardless of the distance between the hand magnifi er and the eye. Although the retinal image size is constant, the fi eld of view decreases as distance is increased. Thus, the relative image size increases compared with the borders of the hand magnifi er. Patients are frequently under the misapprehension that the magnifi cation is greater. Bailey2 has illustrated this concept elegantly (Fig. 10.6).

Figure 10.5 Badal lens system in which the light rays incident on the eye are parallel regardless of the eye-to-lens distance, as the object is at the focal length of the magnifying lens.

The hand magnifi er will provide the improvement in resolution that its Fm suggests, that is, there is a reduction in equivalent

Practical advice

A hand magnifi er should be used within 2× its focal length for fl uent reading, but may be held at more than 4× its focal length if being used for spotting such as prices, etc.

Focal length Parallel light emerging

Eye

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Figure 10.6 A +8.00DS hand magnifi er positioned exactly at its focal length (12.5 cm) as viewed by an emmetrope (or ametrope corrected for distance) for three different lens-to-eye distances (12.5 (top), 25 (middle) and 50 (bottom) cm). The image remains in focus and the retinal image is unchanged in size. The extent of text seen through the magnifi er diminishes greatly as the working distance is increased, and because all emerging light is parallel there is no change in actual image size. There is a change in the perceived image size because the fi eld of view reduces the further away the hand magnifi er is held. Patients sometimes claim that the hand magnifi er provides higher magnifi cation when held further away, but clearly in this case it does not. The relative image size increases in comparison with the borders of the hand magnifi er, not the enlargement power of the magnifi er.

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viewing distance (EVD) directly relating the equivalent power of the hand magnifi er to the reference power of the addition. If reading N24 with a +4.00D near addition (EVD 25 cm), a +16.00D hand magnifi er at fm (EVD 6.25 cm) would give 16/4 = 4; i.e. 24/4 = N6 (and 25 cm/6.25 cm = 4× enlargement ratio).

10.2.3 Maximum Fe: hand magnifi er held at less than fm from eye

When z < fm (i.e. the eye-to-hand magnifi er distance is less than the magnifi er’s focal length), Fe will increase until z = 0 cm, at which:3


but z · FmFa = 0, thus

Fe = Fm + Fa

Practical example

A +20.00D hand magnifi er (Fm = 20.00D, fm = 5 cm) used by a presbyopic patient with a +2.50D addition. If the hand magnifi er is now placed in contact with the reading spectacles:


Fe = +20.00 + 2.50 − (0 × 20.00 × 2.50)

Fe = +22.50 − 0

Fe = +22.50D

In this case, the equivalent power is a maximum and the hand magnifi er is acting directly as a high-powered spectacle addition. This is the principle of calculating equivalent powers of spectacle plus lens magnifi ers. If the original reading addition were +4.00DS (working distance of 25 cm), the working distance of a +16.00DS hand magnifi er held in conjunction with the reading addition would be 100/(16.00 + 4.00) = 100/20.00 = 5 cm.

Thus, the comparison of equivalent viewing distance is between 25 and 5 cm. The enlargement ratio is 25/5 = 5×, which happens to be equal to (Fm/4) + 1 (termed ‘trade magnifi cation’). Trade mag-nifi cation assumes that a hand magnifi er is held in contact with a

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reading addition of +4.00DS (or accommodation of 4D is exerted) and the comparison is made with a reference working distance of 25 cm. For the elderly patient with low vision, this is frequently not a reasonable assumption.

10.2.4 Minimum Fe: hand magnifi er held at z > fm′When z > fm (i.e. the eye-to-hand magnifi er distance is greater than the magnifi er’s focal length:


but z · FmFa = {> Fa}, thus

Fe = Fm + Fa − {> Fa}

and

Fe = {< Fm}

Practical example

A +20.00D hand magnifi er (Fm = 20.00D, fm = 5 cm) used by a presbyopic patient with a +2.50D addition. If the hand magnifi er is held at 20 cm from the spectacle-mounted reading addition:


Fe = + 20.00 + 2.50 − (0.2 × 20.00 × 2.50)

Fe = +22.50 − 10.00

Fe = +12.50D

Thus, no enlargement benefi t is obtained from additional accom-modation and the hand magnifi er delivers considerably less mag-nifi cation than expected. This may still be acceptable for spot viewing or survival tasks and it may represent a more comfortable handling position for the user. As a general rule for fl uent reading, patients should avoid using their reading glasses or bifocal addi-tion unless they can hold the hand magnifi er at or closer than the focal length. Under these conditions they will ensure a level of enlargement commensurate with the power of the hand magnifi er.

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10.3 Field of view

Linear fi eld of view is given by:4

w = y/(Fm · z)

where Fm is the equivalent power of the hand magnifi er, y is the lens diameter (m), and z is the eye-to-hand magnifi er distance. The only patient variable is the working distance (z). Clearly this needs to be as low as possible to maximise the fi eld of view, w.

Examples

• A 5-cm diameter, +20.00D hand magnifi er, held 10 cm from eye:

w = 0.05/(20.00 × 0.1)

w = 0.025, or 2.5 cm (approximately 14 characters of N8 text)


w = 0.05/(20.00 × 0.05)

w = 0.05, or 5 cm (approximately 28 characters of N8 text)


w = 0.05/(20.00 × 0.2)

w = 0.0125, or 1.25 cm (approximately 7 characters of N8 text)

10.4 Summary

• As the enlargement of a hand magnifi er depends on how it is used, the magnifi er should be specifi ed in terms of its dioptric equivalent power, Fm. Practitioners should

Practical advice

The diameter of aspheric hand magnifi ers is often a close approximation to their focal length. Therefore, a hand magnifi er should be used at approximately its diameter from the front of the eye, if Fm is to equal Fe.

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avoid using manufacturers’ ratings of power expressed as magnifi cation.

• When used by an emmetrope or corrected ametrope, the dioptric equivalent power of the system is exactly that of the hand magnifi er itself. The only variable is the fi eld of view, which is determined by the hand magnifi er-to-eye separation.

• When using a reading addition, the hand magnifi er-to-eye distance must be zero if the aid is to achieve its rated power or ‘trade magnifi cation’ (presuming a +4.00D reading addition or 4.00D of accommodation is exerted). At any greater hand magnifi er-to-eye distance, the equivalent power is less than its ‘rated’ power.

• At hand magnifi er-to-eye distances equal to the focal length, the equivalent power of the system is equal to the equivalent power of the hand magnifi er, irrespective of reading addition or accommodation.

• At hand magnifi er-to-eye distances greater than the focal length, the equivalent power of the system is dramatically reduced when used in conjunction with a reading addition. Long hand magnifi er-to-eye distances are adequate for lower power hand magnifi ers, and hence are familiar to patients. Many patients adopt these familiar distances when using higher power hand magnifi ers, and are disappointed with the results.

• The wider aperture of lower power hand magnifi ers helps the patient to control eye movements and maintain reading fl uency. Thus, for reading tasks, the goal of the clinician is to optimise the fi eld of view by ensuring a hand magnifi er-to-eye separation no greater than the focal length of the hand magnifi er, provided the gains in equivalent viewing power are suffi cient. Lighting of the task should also be optimal.


• Demonstrate to the patient that when the hand magnifi er rests on the near task it offers virtually no enlargement: as the hand magnifi er is raised the enlargement increases, but only until the magnifi er-to-task distance is equal to the focal length.

• Practitioners must make themselves familiar with the focal length ( fm) of the hand magnifi ers they prescribe. Viewing at

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this hand magnifi er-to-task distance will optimise the fi eld of view.

• Patients must be encouraged to use their distance prescription if the eye-to-hand magnifi er distance is greater than the focal length of the lens ( fm) and their near prescription if the focal length of the hand magnifi er ( fm) is less than the eye-to-magnifi er distance.

• Reading tasks are facilitated if the object itself can be held rigid. Thus, a newspaper should be folded to expose only one column, or a clipboard could be used.

References

1. Bailey IL. Combining accommodation with spectacle additions. Optometry Monthly 1980; 71:397–399.

2. Bailey IL. Magnifi cation for near vision. Optometry Monthly 1980; 71:119–122.

3. Johnston AW. Technical note: the relationship between magnifi cation and fi eld of view for simple magnifi ers. Australian Journal of Optometry 1082; 65:65–68.

4. Johnston AW. Understanding how simple magnifi ers provide image enhancement. Clinical and Experimental Optometry 2005; 86:403–408.

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The task-to-lens distance in a magnifi cation system is critical, as was illustrated in Chapter 9. In addition, most people with visual impairment are elderly and often have hand tremors or suffer fatigue after even relatively short periods of having to support a hand magnifi er steadily. Therefore, being able to support the magnifying lens without using the hand to sustain a fi xed lens-to-working plane distance is an attractive option (Table 11.1).

Although low-powered stand magnifi ers are available, they are often bulky as a tall stand is required to ensure that the lens-to-working plane distance approaches Fm. These aids often have large-diameter lenses, which tend to be heavy and bulky. Owing to the more critical focus required of higher powered lenses, the range of medium- to high-powered stand magnifi ers available is greater than that of hand magnifi ers. As it is frequently diffi cult to perform tasks beneath high-powered stand magnifi ers, they often have solid sides and built-in illumination.

As for hand magnifi ers, stand magnifi ers are frequently im-properly understood by practitioners because they do not seem to provide the stated enlargement (see Ch. 9), and pati-ents complain of the generally poor fi eld of view (due to the

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Stand magnifi ersJames S. Wolffsohn

111111

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high power of the lenses and a failure to use a reduced working distance).


Most stand magnifi ers have a fi xed focus, although they can consist of a lens (typically low powered and with spherical surfaces) sus-pended around the neck on a cord (often termed a ‘chest’ magni-fi er) or held on an adjustable or fl exible ‘arm’ (Fig. 11.1). Only a few high-powered stand magnifi ers allow variable focusing. By using a fl exible arm with clamps at either end, a hand magnifi er can be secured to create a stand magnifi er when the user needs their hands free.

11.2.1 Variable focus stand magnifi ers

In variable focus stand magnifi ers, the distance between the object plane and the lens can be freely selected by the patient, so these magnifi ers can be used essentially as a ‘steadied’ hand magnifi er.

Table 11.1 Advantages and Disadvantages of Stand Magnifi ers


The working distance between Low-power stand magnifi ers are the lens and task is easily generally large because they have tomaintained, even when the maintain a long working distance andpatient has a hand tremor support a large lens

Hands are free to perform The required reading addition istasks beneath the lens, when dependent on the lens power, lens produced in low powers design and distance between the lens and the task, and is therefore diffi cult to calculate

Usually include built-in Diffi cult or impossible to performillumination and exclude tasks beneath, when produced in external glare sources higher powers

Moderately priced More expensive when supplied with a mains-operated system

Need a fl at stable surface to rest on

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This type of low vision aid is particularly valuable to the model maker or crafts enthusiast, although supplementary lighting is almost essential. These stand magnifi ers can also be valuable as a writing aid.

11.2.2 Fixed focus stand magnifi ers

Fixed focus stand magnifi ers (Fig. 11.2) are typically designed so that the magnifi er lens-to-object plane distance is less than the anterior focal length of the lens, and hence the light leaving the lens is divergent. The light must therefore be converged before reaching the retina (Fig. 11.3). This can be achieved by ocular accommodation and/or through the use of a near reading addition (Fa), so that parallel light enters the eye. The optical system can therefore be considered to have two components, separated by (z) cm, whose Fe is determined by:


where Fe is equivalent power of the system, Fm is equivalent power of the stand magnifi er, Fa is power of add/accommodation, and z is the eye-to-magnifi er distance.

Figure 11.1 A range of variable focus ‘chest’ and fl exible ‘arm’ stand magnifi ers.

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Figure 11.2 A range of fi xed focus stand magnifi ers.

Practical example

A 20.00D stand magnifi er (Fm = 20.00D, fm = 5 cm) used by a presbyopic patient with a +2.50D addition. If the stand magnifi er lens is placed 10 cm in front of spectacle lens:


Fe = +20.00 + 2.50 − (0.10 × 20.00 × 2.50)

Fe = +22.50 − 5.00

Fe = +17.50D

11.3 Vergence of light

As noted in Section 11.2, the stand magnifi er lens-to-object plane distance is generally less than the anterior focal length of the lens. If the stand height for the magnifi er described above was 3.33 cm, then, as the focal length of a +20.00D lens is 5 cm, the emergent

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light leaving the stand magnifi er would be divergent. The ver-gence of light reaching the stand magnifi er (L) from the object 3.33 cm away is:

L = 1/− stand height (m) = 1/−0.0333 = −30.00D

The vergence of light leaving the stand magnifi er (L′) with lens power +20.00D is:

L′ = L + Fm

= −30 + (+20.00) = −10.00D

l′ = image distance = 1/−10.00 = −0.10 m = −10 cm

If the patient’s eye is right against the stand magnifi er (z = 0), the image created by the stand magnifi er alone would be 10 cm in front of the eye, and +10.00D of accommodation and/or a reading addition would be required to neutralise the divergence of light. The enlargement would be:


= +20.00 + 10.00 − (0 × 20 × 10) = 30.0D

Enlargement = Fe/4 = 30.0/4 = 7.5×

As the eye-to-magnifi er lens distance increases, the enlargement decreases and the power of accommodation and/or reading addi-tion decreases. If the stand magnifi er-to-eye distance increases to 30 cm (z), the image will be positioned 40 cm from the eye:

z + l′ = (−30) + (−10) = −40 cm

Figure 11.3 Divergent exit light from a fi xed focus stand magnifi er. (Redrawn with permission from Dickinson 1998.1)

FM

I´I

L

F

L´

z

fM

FA

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requiring accommodation and/or a reading addition of +2.50D to focus the image clearly on the retina. Hence the enlargement of the optical system is now:


= +20.00 + 2.50 − (0.30 × 20 × 2.5) = 7.5D

Enlargement = Fe/4 = 7.5/4 = 1.9×

11.3.1 Optimising the reading addition

The accommodation/reading addition cannot be greater than the divergence of light leaving the stand magnifi er lens, or a clear image of the object on the retina cannot be formed.

If the patient can lift the stand magnifi er to improve the image focus, the reading addition is insuffi cient. Conversely, if the vision becomes worse when the stand magnifi er is lifted off the object, this suggests that the reading addition is already too high and the

Practical advice

In general, the lower the power of the stand magnifi er, the higher the emergent vergence and the more complex the lens design (such as aspheric).

This allows a smaller stand than would otherwise be required with lower powered stand magnifi ers, and allows a further magnifi er lens-to-eye distance, although there is a corresponding loss of fi eld of view and enlargement.

Practical advice

It is an expensive option to prescribe an additional pair of reading glasses for the presbyope who wishes to use a stand magnifi er. Patients should be encouraged to bring all their old glasses to a low vision assessment in order that the most appropriately powered pair can be coupled with a suitably designed stand magnifi er and advice on the optimal working distance given.

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eye-to-magnifi er lens separation will need to be decreased. The reading addition can be modifi ed subjectively by superimposing trial lenses on the patient’s existing reading correction while the stand magnifi er is used at the intended working distance. This can be achieved through the use of the Halberg trial clip, as attempting to hold a lens in position as the patient uses the low vision aid tends to be clumsy and the patient may feel pressed into making a rapid response.

11.3.2 Measuring the emergent vergence of a stand magnifi er

The emergent vergence from the lens can most easily and objec-tively be determined by (Fig. 11.4):

• Focusing reversed light rays: Tape a piece of thin paper, or use translucent tape, across the base of the stand magnifi er (object

Figure 11.4 A, A distant light source is imaged through the stand magnifi er on to a translucent surface attached to its base (object plane) and the trial lens over the magnifi er lens is altered until the image appears in focus. B, The observer views the stand magnifi er image through a distance focused telescope and alters the trial lens between them until the emergent rays are parallel and the image appears in focus. (Redrawn with permission from Dickinson 1998.1)

A B

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plane) and image a distant source of light (essentially parallel rays typically from a strip fl uorescent tube or illuminated letter chart) on the paper or tape through the stand magnifi er (Figs 11.4A & 11.5). Positive lenses can then be placed on top of the stand magnifi er lens until the image is optimally focused. This lens is of equal power, but of opposite direction, to the emergent vergence.

• Focusing the emergent light rays with a telescope: Using a distance telescope, which is more sensitive to defocus (see Ch. 13), one can more easily determine when a positive lens placed on top of the stand magnifi er lens neutralises the emergent vergence, thus producing a clear retinal image (Figs 11.4B & 11.6).

11.4 Field of view

Linear fi eld of view is given by:2

w = y/Fm(z)

where Fm is equivalent power of the stand magnifi er, y is the lens diameter (m), and z is the eye-to-magnifi er distance.

A BFigure 11.5 A,B, Calculating the emitted vergence of a stand magnifi er using a distant object.

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Figure 11.6 Calculating the emitted vergence of a stand magnifi er using a distance focused telescope.

The fi eld of view may be limited by the dimensions of the mag-nifi er stand.

11.5 Bar and fl at-fi eld magnifi ers

Bar and fl at-fi eld magnifi ers (Table 11.2) are diffi cult to character-ise as they are designed to be placed on an object and, as such, are similar to stand magnifi ers. The lens is not, however, raised above its base (except in the case of more recently produced plastic ver-sions where the lens is raised slightly above its base by a surround, a design feature incorporated to reduce surface scratching). The enlargement produced is real, similar to that of an electronic vision enhancement system (see Ch. 14). These magnifi ers are also known as ‘paperweights’, ‘bright fi eld’ and ‘Visolett’ magnifi ers.3 Flat-fi eld magnifi ers are a single solid hemispherical lens, which may have material removed from the top and bottom to leave a rectangular

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Table 11.2 Advantages and Disadvantages of Bar and Flat-Field Magnifi ers


Light-gathering properties Needs a fi rm fl at surface(Fig. 11.7)

Few refl ections Only a limited horizontal fi eld of view with fl at-fi eld magnifi ers due to the weight and bulk of larger hemispheres. Creating in plastic reduces the weight (but is more susceptible to scratches), as does truncation of the upper and lower fi eld

Binocular viewing at a normal working distance

Unaffected by a hand tremoras rests on the page

Few aberrations in the lens periphery

Often seen as a toy by Enlargement in only one directionchildren, rather than an with bar magnifi ersunsightly visual aid

Available in a range of No access to material underneathdiameters to suit everything from large desktop paperweight to small coin-sized pocket version

viewing window, allowing a larger hemispherical lens to be used (increasing the fi eld-of-view width) without adding excessive weight. Bar magnifi ers are single solid lenses of hemicylindrical shape that magnify only in the vertical direction when the length of the magnifi er is positioned horizontally (usually along a line of text). Many of these bar magnifi ers are produced with a line guide inscribed, often in red, on their lower surface. Some, such as the VTM dome, have a viewing box designed to highlight only several words at a time (Fig. 11.7).

The enlargement can be calculated from (Fig. 11.8):

Enlargement = nr/(t(1 − n) + nr)

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Figure 11.7 Bar and fl at-fi eld magnifi ers.

Figure 11.8 Enlargement calculation. (Redrawn with permission from Dickinson 1998.1) RoC, radius of curvature; Obj, object plane; Img, image plane.

RoC Obj ImgNE

trll´

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where t is the magnifi er thickness, r is the spherical radius, and n is the refractive index.

If the magnifi er is exactly hemispherical, t = r, so:

Enlargement = n

The maximum enlargement occurs when the magnifi er is spheri-cal (although an infi nitesimally small area would be in focus with the bar or fl at-fi eld magnifi er fl at on the object) and t = 2r:

Enlargement = n/(2 − n)

Therefore, the smaller the proportion of the sphere that is removed, the higher the enlargement created, but at the expense of the fi eld of view. In practice, enlargement is generally up to 3×. The image is formed close to the original object, regardless of the bar or fl at-fi eld magnifi er thickness. Hence enlargement is not created by a reduction in viewing distance (as with other plus lens magnifi ers) and the fi eld of view is not increased by decreasing the eye-to-magnifi er distance. The diameter of the lens alone determines the fi eld of view. The image is formed close to the patient’s normal working distance, so the bar or fl at-fi eld magnifi er can be used with no change in posture and with normal reading glasses. Binocular viewing is also possible.

11.6 Summary

• The vergence of light emerging from a fi xed focus stand magnifi er should be measured, so that an appropriate recommendation on the use of a reading addition can be made.

• Advice should be given on the working distance between the magnfi er lens and the eye as this effects both the magnifi cation and the image focus.

• As with hand magnifi ers, power should be specifi ed in terms of the dioptric equivalent power, Fm. Practitioners should avoid using manufacturers’ rated magnifi cation powers.

• Bar magnifi ers magnify in only one direction.• The larger the proportion of a sphere used to create a fl at-fi eld

magnifi er, the higher the magnifi cation, but the smaller the fi eld of view.

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• Demonstrate to the patient that stand, bar and fl at-fi eld magnifi ers work best if laid fl at on the object of interest.

• The use of reading glasses is usually appropriate because of the emerging vergence of light from a stand magnifi er, although this should be optimised with trial lenses or the emerging vergence calculated.

• If the object of interest is not stiff, placing it on a clipboard can improve handling and maximise the clarity over the whole fi eld of view.

• Bar and fl at-fi eld magnifi ers allow binocular reading at the patient’s habitual working distance with their normal reading glasses. Field of view is not enhanced by decreasing the eye-to-magnifi er separation.

References

1. Dickinson C. Low vision: principles and practice. Oxford: Butterworth-Heinemann; 1998.

2. Johnston AW. Technical note: the relationship between magnifi cation and fi eld of view for simple magnifi ers. Australian Journal of Optometry 1982; 65:65–68.

3. Fonda G. Visolett magnifi er evaluation and optics. Archives of Ophthalmology 1076; 94:1614–1615.

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A spectacle magnifi er is any lens mounted in the spectacle plane with a front vertex power greater than that used as a conventional reading addition. To all practical intent this means a dioptric equivalent power of +4.00DS or greater, as few clinicians would prescribe a normally sighted patient with a reading addition neces-sitating a working distance of 25 cm or closer. This magnifying lens may be monocular or binocular, spherical or aspheric, single vision, bifocal or even multifocal. It may be integral or multi-element in construction, modular or customised from components. It differs from a telescope in having no vergence amplifi cation. In certain cases and in certain texts the term spectacle microscope has been used. This has been confused with other multi-element items such as near telescopes, and this chapter will not use this terminol-ogy. The main advantage of spectacle magnifi ers are that they meet patients’ desire ‘just to have stronger reading glasses’. However, they provide enlargement at the expense of working distance (Table 12.1).


The spectacle magnifi er provides for an increase in retinal image size by increasing the front vertex power, enabling a closer working

223

CHAPTER

Spectacle magnifi ersNicholas J. Rumney

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distance to be used effectively. It thus provides a form of relative distance enlargement (also termed proximal enlargement) and as such is practically indistinguishable from a myope holding text at their far point, or indeed an emmetrope or corrected ametrope accommodating to a reduced working distance. For many patients who have low vision with active accommodation (i.e. children and young adults), near enlargement is obtained simply by holding the material closer and accommodating to the new distance. In these circumstances the terminology outlined in Chapter 9 (equivalent viewing power and equivalent viewing distance) enables the practitioner to establish the relative enlargement.

Although various calculations can be made with regard to the exact enlargement of plus lenses in the spectacle plane, these are of no practical signifi cance in the consulting room. In this chapter, specifi c products are outlined, as there are limited options on the

Table 12.1 Advantages and Disadvantages of Spectacle Magnifi ers


Cosmetically and psychologically Conspicuous if clip-on or head-bandacceptable mounted

Hands are free to perform tasks Shorter working distance than other low vision aids of the same equivalent power

Large fi eld of view

May fl ip-up, or out, of the line of Clip-on and head-mountedvision magnifi ers may have mechanical problems

May incorporate correction for May be heavy and physicallypatient’s ametropia constricting

Binocular single vision may be Can be diffi cult to sustain binocularpossible with decentration or single visionprismatic component

May be provided under GOSvoucher scheme

GOS, General Ophthalmic Services.

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market and generally these aids are prescribed only by more spe-cialist units.

12.3 Reducing the working distance

Increasing the reading addition reduces the working distance (Table 12.2). Thus, to use this form of enlargement the patient must be able to accept and tolerate the change in working distance. For the young patient with ample accommodative amplitude this is likely to come as naturally as it will for the uncorrected myope. For example, it is much harder for the elderly patient to adapt to a close working distance if, before the onset of visual impairment, they were used to working at 40 cm and using a +2.50 addition, although it is by no means impossible and certainly not at all unusual.

Table 12.2 Working Distances Required with a Range of Reading Additions

Dioptric power Working Enlargement Enlargement

of add distance (cm) from 33 cm from 25 cm

+3.00 33 1 0.8

+4.00 25 1.3 1

+5.00 20 1.7 1.3

+6.00 16.7 2 1.5

+8.00 12.5 2.7 2

+10.00 10 3.3 2.5

+12.00 8.33 4 3

+16.00 6.25 5.3 4

+20.00 5 6.7 5

+24.00 4.17 8 6

+32.00 3.12 10.7 8

+40.00 2.5 13.3 10

+48.00 2 16 12

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Dispensing high-powered near additions requires care. At collec-tion the practitioner should have a near chart immediately to hand and be careful to place the spectacles on the patient’s nose sitting slightly low, so that the patient can look over the lenses. The blur-ring induced at distance will be less disorienting when the spec-tacles are positioned in this manner. The practitioner (preferably the same one who conducted the initial assessment) should intro-duce the reading chart at the specifi c distance and initially dictate the working distance required to ensure clear focus. Most patients instinctively push the material further away if the chart is simply handed to them.

The natural feel of a close distance is dictated by the dis-tance between the hands (Fig. 12.1). Holding a broadsheet newspaper, arms outstretched, dictates an arm’s length work-ing distance. Folding to tabloid size reduces the comfortable working distance naturally to that of the lap, whereas folding the material into a vertical column (still with both hands on either side) brings it closer still and, in addition, makes the object rigid.

Table 12.2 illustrates the working distances required with a range of reading additions. Note the logarithmic series: on either column a change of three cells up or down denotes a halving or doubling of the power or distance – hence the fact that spectacle magnifi cation is in reality relative distance enlargement. A doubling of the near addition will result in a halving of the working distance and hence a doubling of the retinal image size. The enlargement ratio, or relative gain in retinal image size, clearly depends on the initial reading addition or working distance habitually adopted. Typical values are given in column three (33 cm starting addition) and column four (25 cm starting addition).

Practical advice

Use a shallow or half-eye frame when prescribing a high-powered spectacle near addition for an emmetrope or those with minimal refractive errors. This enables the patient to look over the top without signifi cant spectacle blur. The ametrope may not have perfect vision unaided, but it is unlikely to be as unnatural or isolating as the single vision view through a full-aperture spectacle magnifi er lens.

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12.4 Need for occlusion

It is often the case that poorer reading performance is achieved with both eyes open. Patients are usually unaware of this, and the phenomenon, when demonstrated to them, can be diffi cult to accept. Preconceptions about not wanting to overwork the better eye or further damage the poorer eye through occlusion may be diffi cult to dispel. Poor binocular performance may be for one of two reasons:

1 Suppression – for example, when a patient has lost sight in the dominant eye and becomes reliant on an amblyopic eye. The visual system may fi nd it extremely diffi cult to accept the image from the amblyopic eye as the principal image, without total occlusion of the fellow eye. Under these circumstances binocular versus monocular contrast sensitivity may be the only clinical measure to confi rm ocular predominance.

A B

C DFigure 12.1 A–D, The acceptability and natural feel of a close working distance is determined by the distance by which the hands are held apart. A newspaper under ×5 enlargement is nearly four feet across! Ask the patient to roll the newspaper up to one column’s width and to lean into it. This also keeps the newspaper more rigid.

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Frequently there is no actual clinical evidence of improvement with occlusion, and a detailed history should always include the question: ‘Do you ever close one eye when reading or watching television for example?’

2 The demands of working distance and front vertex power may not permit the visual axes to be accurately aligned for binocular viewing of the object of regard (even with the use of prisms). This is typical for dioptric equivalent powers greater than +16.00DS. Care should therefore be taken to align visual axes with prism or decentration if binocular use of high-powered near additions is required.

In these situations it is best to experiment with different options for the non-dominant eye, such as a balance prescription or a plano, frosted, chavasse or matt black lens. Adhesive frosted or blackened plastic fi lm of differing occlusive types and densities is a useful part of the low vision armoury.

The need for occlusion may be demonstrated by comparing bin-ocular with monocular measures of visual performance, such as distance and near visual acuity, contrast sensitivity and reading speed.

12.5 Binocular spectacle enlargement

It is possible to achieve binocularity with spectacle enlargement as long as the optical centres of the lenses are coincident with the object of regard at the working distance dictated by the front vertex power of the lens. This may be achieved by decentration or by adding base-in prism.

Off-the-shelf prism high-powered near addition readers are remarkably successful (Fig. 12.2). If a prescription is to be made up specifi cally for a patient, rather than using an off-the-shelf item, the required decentration should be calculated (Fig. 12.3). The

Practical advice

Make sure you have supplies of occlusive tape. 3M Magic Sellotape® is an excellent temporary occluder.

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229

Figure 12.2 A range of binocular high-powered near addition readers.

decision as to whether this may be better achieved by worked prism or simple decentration can be made by the prescriber or left to the prescription house.

Many workers have adopted or suggested rules of thumb to allow calculation of decentration and/or prism. For example, decentration in millimetres (i.e. the difference between the dis-tance and near pupillary distance [NPD]) is estimated as the required object-to-lens distance (in dioptres) ×1.51 or ×2.0.2 Bailey’s method1 also added 1 mm if the pupillary distance was greater than 65 mm. As the required decentration can become too large to be practical, Fonda2 suggested 1Δ per dioptre of object-to-lens distance as an alternative.

If an emmetropic patient with an interpupillary distance (PD) of 67 mm is prescribed a reading addition of +12.00D as a single vision lens:

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Bailey: decentration = working distance × 1.5 (+1 mm if PD >65 mm) = (12.00 × 1.5) + 1 = 19 mm

Therefore:

NPD = PD − 19 mm = 48 mm

Fonda: decentration = working distance × 2.0 = (12.00 × 2.0) = 24 mm

Therefore

NPD = PD − 24 mm = 43 mm

or

Base-in prism = 1Δ per dioptre of object-to-lens distance = 12Δ

Unfortunately these rules of thumb are generally imprecise as they fail to account for the interpupillary distance of the patient.

Figure 12.3 The trigonometric calculation needed to determine decentration (h) based on knowledge of the interpupillary distance (PD 58 mm; half-PD 29 mm), working distance of the object of regard (+10DS = 100 mm) and back vertex distance (BVD 12 mm), and an assumed ocular radius (OR) of 15 mm.

29/(12 + 15 + 100) = h/(12 + 15)29/127 = h/27h = 27(29/127)h = 6.2 mm

12 mm

PD58 mm

100 mm

BVD

Visual axis for distance

Near visual axis

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12.6 Prismatic half-eye spectacles

A simple and useful range of off-the-shelf single vision high-powered near additions is available in the form of prismatic half-eyes, where a standardised range of powers is combined with specifi c prismatic correction, enabling binocular single vision at the appropriate working distance. For example, Coil manufactures two frame colours (crystal and brown mottle) in two sizes cover-ing a range of powers (Table 12.3).

12.7 Spherical spectacle magnifi ers

In this group is included all plus lens types, including torics that do not incorporate an aspheric surface. Because a high myope may use a high-powered near addition that is less than their spectacle correction, high-powered near additions in this situation may be negative lenses or even no lens at all if the myope reads without a correction at the ocular far point.

12.7.1 High-powered addition single vision

In this category most of the lenses will be plus and of powers that require careful dispensing if cosmetically acceptable spectacles of

Practical example

A patient has the following distance correction:

R +2.75/−1.00 × 90L +3.50/−0.75 × 110

and requires a +6.00D add in a round 24 segment bifocal. The PD is 62 mm and the vertex distance is 12 mm.

h/(15+12) = 31/(167+12+15)

Thus h (decentration in millimetres) is (31 × 27)/194 = 4.3 mmThe lenses are ordered with a 4.5 mm inset. This can be achieved

with either a fl at top or a round segment bifocal, although laboratories fi nd the decentration of round segments by rotation easiest.

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Table 12.3 Coil Range of Prismatic Half-Eye High-Powered Near Additions with Base-in Prism

Part no. Temple (mm) Size Frame

+4.00 equivalent power OU 6D BI OU prism

4146/01 140 45/24 Brown4147/01 140 45/24 Crystal4148/01 145 49/26 Crystal4149/01 145 49/26 Brown











Note: All powers are equivalent and not back vertex. Coated with Rubfast abrasion-resistant coating. For uncoated lenses delete /01 suffi x. BI OU, base in prism, both eyes.

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reasonable weight are to be produced. If conventional lenses are prescribed, decentration from a large uncut lens may be the most cost-effective solution. Although lenticulars are used less com-monly these days, they are an effective way of achieving thinness with good cosmesis in small frames.

Eschenbach spectacle-mounted reading aids

In recent years Eschenbach have developed a series of spectacle-mounted reading aids including the lightweight Labo Clip-ons, which are available in binocular (×1.7–3) and monocular (×4 and ×7) forms. They also have preassembled Prismatic Bino Comfort, which are reduced aperture, high add, reading spectacles (4D, 6D, 8D and 10D), and Aplanatic Comfort, which are full aperture spectacle magnifi ers (12D, 16D, 20D, 24D, 28D and 32D). Most importantly, Eschenbach have recently introduced the lightweight, aesthetically excellent, Novo Bino/Mono spectacle magnifi ers, which utilise diffractive optics. The monocular spectacles are available in four powers (12D, 16D, 20D and 24D), whereas the binocular equivalents are available in lower powers with pre-worked base in prismatic components (4D/5Δ, 5D/6Δ, 6D/7Δ, 8D/9Δ, 10D/11Δ).

12.7.2 High-powered addition bifocal

Many high add bifocals are produced, and various ranges of fi n-ished lenses are available from the larger prescription houses (e.g. Norville and Zeiss). Typically, additions of up to +16D are avail-able with a 25-mm round segment (e.g. SOLA LVA 25). Near addi-tions up to +8D are available in fl at-top bifocal designs (although these have a small maximum diameter), and of course Franklin splits can be created for virtually any prescription. Care needs to be taken in selecting the lenses as there may be a limited range of uncut diameters and distance corrections available. If an unusual segment inset is required, the ordering needs to be easily under-standable, preferably in terms of distance and near interpupillary distance rather than prism. The inset limit on a round segment is half the segment diameter; for a fl at top, this depends on the front surface moulding of the semi-fi nished lens. Consideration should also be given to the Keeler LVA 12, which is a threaded plus lens 25 mm in diameter that can be screwed into a threaded hole in a plastic spectacle lens or into an adhesive mount (Keeler advanced

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system), if the power of the carrier lens (e.g. for a cylindrical com-ponent) is required. An advantage of this is that the optical centre can be placed wherever desired. The power range is from +8DS to +48DS.

12.8 Aspheric spectacle magnifi ers

It was recognised by Lederer and others that high-powered plus lenses in a form appropriate for distance vision may give poor results when used for near objects. This is because of the aberrations produced – chiefl y oblique astigmatism and coma, but also distortion. It is important to note that, if aspheric lenses are chosen in the interests of weight and thickness, prism has to be worked to achieve the desired effect as the effect of decentration will be minimised owing to the change in power across the lens surface.

12.8.1 Coil Hyperocular

In the 1950s Arthur Bennett designed a range of lenses that are still marketed under the Coil Hyperocular range.3 These lenses are made in polymethylmethacrylate (PMMA; hence their old name, Igard Hyperocular). They are little utilised in routine optometric practice, but are an essential part of every low vision optometrist’s armoury (Table 12.4). They have a good range of power, give a high image quality, and are light, cosmetically acceptable and reasonably inexpensive. When regarded as high-powered plus lenses, they have one other advantage in that they fall into the various categories or voucher bands of the National Health Service voucher system, which helps with the cost of provision to eligible patients.

Hyperoculars are bi-convex injection moulded lenses with an aspheric front surface and a spherical back surface. They cannot be obtained with any prismatic or astigmatic correction, and all are too powerful to enable binocular alignment. However, they are quite versatile as they can be glazed to almost any frame of suit-able diameter (half-eyes with care), and can even be made into ‘Franklin split’ bifocals. This lens reaches its apotheosis in the Swedish ‘multi-lens’ concept, in which precision machining enables segments of the Hyperocular and any other lens form to be inserted wherever required.

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Coil ready-made Hyperoculars

Hyperoculars are now also available in glazed rather than uncut form. These are intended for off-the-shelf prescribing, and the glazed frame can be ordered with a Hyperocular in either right or left (or even both) lens apertures. Single vision lenses can be optionally ordered as frosted, plano or black occluded (Table 12.5).

12.8.2 Keeler LVA 9, 10; Redi-fi t

Keeler is perhaps best known for their A series approach to the specifi cation of enlargement, and also for their spectacle-mounted near telescopes. However, they also have a range of non-aspheric and aspheric spectacle magnifi ers. These are mostly modelled on the Coil Hyperocular – in fact some of the lenses are simply Coil lenses in Keeler mounts. The difference is that their construction is modular, enabling systems to be assembled without complicated

Table 12.4 Aspheric Hyperocular Lenses (COIL): Current Range of Six Lens Powers

Part no. Diameter Aperture Enlargement

5371/01 Ø65.0 Ø40.0 Aperture 4×

5343/01 Ø49.6 Ø40.0 Aperture 4×

5372/01 Ø65.0 Ø38.0 Aperture 5×

5344/01 Ø49.6 Ø38.0 Aperture 5×

5373/01 Ø65.0 Ø36.0 Aperture 6×

5345/01 Ø49.6 Ø36.0 Aperture 6×

5374/01 Ø65.0 Ø34.3 Aperture 8×

5347/01 Ø49.6 Ø34.3 Aperture 8×

5375/01 Ø65.0 Ø32.0 Aperture 10×

5376/01 Ø65.0 Ø30.0 Aperture 12×

The original four Arthur Bennett lenses (4× , 5× , 6× , 8×) were added to when Professor M. Jalie designed the 10× and 12× lenses.

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glazing and also permitting the incorporation of prescription cells (for correcting refractive errors, including astigmatism) via a rear element. Some of these, for example the Stedi-fi t 10c, have distance pieces of clear acrylic, enabling precise posture to be held (Fig. 12.4A). Others, such as the HI MAG-LVA 9 (Fig. 12.4B), can be attached to a light source. All can be adapted to contain a prescrip-tion cell in the rear of the lens.

Table 12.5 Coil Ready-Glazed Hyperocular Microscopic Spectacles

Part no. Lens description

4× magnifi cation3146/01 OU3147/01 OD Plano3148/01 Plano OS






All spectacles have a brown frame. Coated with Rubfast abrasion-resistant coating. For uncoated lenses delete /01 suffi x. OD, right eye; OS, left eye; OU, both eyes.

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Keeler Redi-fi t

The Keeler Redi-fi t system is a monocular spectacle-mounted high-powered plus addition that attempts to simplify this type of low vision aid (LVA) by adopting a modular approach to the use of pre-existing LVAs from Keeler’s wide range (Table 12.6). By standardising frame and lens types, the device can be quickly made up, loaned and prescribed. If it is deemed unsuitable after trial use, the enlargement can be modifi ed as required, or it can be broken down back into the original components and returned to stock. This means that the only cost incurred is chair time.

The Redi-fi t testing set

Keeler have designed a new spectacle frame with a shallow, sym-metrically oval, lens shape. Thus the right and left eyes can use the same lens. The frame will take the standard Keeler (34 mm circular) spectacle lens known as the LVA10, and the testing set consists of six lenses (labelled 2×, 3×, 4×, 5×, 6×, 8×) and a frosted occluder along with three frames of differing bridge and side

A BFigure 12.4 A, Keeler Stedi-fi t 10c. B, Keeler HI MAG-LVA 9.

Practical advice

Modular hyperoculars can be useful in training patients to accept the close working distance of the high-powered plus lens before prescribing the cosmetically superior Coil Hyperocular in either a full-aperture or half-eye frame.

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dimensions. The set sits in a convenient plastic box. A complimen-tary part of the kit is a set of pre-glazed lenses (the same powers as in the trial set) for immediate dispensing. With the lenses being restricted to monocular use, the precise centration is less im-portant than it might otherwise be. The lenses themselves are either conventional high-powered plus (2× and 3×) or the Coil Hyperocular.

The practitioner thus has a choice when making up the specta-cles. The screw-together modular lenses (from the trial set) can be used, or the pre-cut lenses can be sprung into the frame for which-ever eye is desired, occluding the other. There is no provision for using these devices binocularly, and pre-cut lenses have optical and geometric centres that are identical.

12.8.3 Power and magnifi cation

The Redi-fi t is rated in terms of magnifi cation (Table 12.7), but the rated enlargement of the device is dependent entirely on the start-ing point (see Ch. 9).

Table 12.6 Component Codes for Ordering Keeler Redi-Fit

Item Size or power Code

Redi-fi t trial set 2280-P-1065

Frames (18 dbl) 4080-P-2222

Frames (20 dbl) 4080-P-2214

Frames (22 dbl) 4080-P-2329

Pre-cut 2× 2185-P-5578

Pre-cut 3× 2185-P-5578

Pre-cut 4× 2185-P-5578

Pre-cut 5× 2185-P-5578

Pre-cut 6× 2185-P-5578

Pre-cut 8× 2185-P-5578

Pre-cut plano 2185-P-5578

Pre-cut occluder 2185-P-5578

dbl, Distance between lenses.

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Comparison with near telescopes

Telescopes have a greater working distance than the equivalent near single plus lens of the same equivalent power. However, near telescopes achieve their enlargement through a combination of telescope and cap. Therefore a 6× telescope and a +4D cap will have a front vertex power (FVP) of +4DS (25-cm working distance) and a +24D equivalent power. A +24DS equivalent power plus lens will have a FVP of +24DS and a working distance of 4.16 cm. There is an obvious increase in working distance from 4.16 to 25 cm, which, not coincidentally, is a 6× change. However, when a 1.6× telescope is used in conjunction with a +20DS cap it will have a working distance of 5 cm and an equivalent power of +32DS. A single plus lens of equivalent power +32DS will have a working distance of 3 cm. The relative gain of between 3 and 5 cm is insig-nifi cant compared with the gains in cosmesis from using a single plus lens such as a hyperocular.

12.9 Summary

• A spectacle magnifi er is any lens, in whatever form, mounted in the spectacle plane with a front vertex power greater than +4.00DS.

• Spectacle magnifi ers require careful dispensing with lens centration, prism and occlusion as appropriate.

• Various off-the-shelf options are available to the low vision practitioner that enable effi cient trialling and prescribing of spectacle magnifi ers.

Table 12.7 Optical Parameters of the Redi-Fit System

Lens name Rated Equivalent Working

magnifi cation power (Fe) distance (cm)

10-1 2× +8.25 14

10-2 3× +13.00 10

10-3 4× +17.50 7

10-4 5× +20.50 6

10-5 6× +27.75 5

10-11 8× +32.00 4

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• Always demonstrate a spectacle magnifi er to patients, as it is usually the desired option. If they choose to reject the short working distance, this gives an appropriate opportunity to discuss other low vision aid solutions.

• Always check patients’ previous prescriptions as sometimes they already have a pair of spectacles suitable for the task requirement.

• Never re-glaze a patient’s only pair of spectacles for near with a high-powered near addition, as the patient will need a pair of glasses for everyday tasks of lower visual demand, such as eating.

• A demonstration stock of clip-on loupes is always useful to demonstrate spectacle magnifi cation.

References

1. Bailey IL. Centering high-addition spectacle lenses. Optometry Monthly 1979; 70:523–527.

2. Fonda G. Binocular correction for low vision: rationale for rule of thumb for decentration. American Journal of Ophthalmology 1957; 45:23–27.

3. Bennett AG. Igard Hyperoculars: their origins and development. Ophthalmic Optician 1975; 15:1151–1154.

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Telescopes increase angular subtense without requiring a change in working distance, and hence are ideal for tasks that have to be undertaken at far and intermediate distances, such as spotting bus numbers and reading music. They are also useful when undertak-ing near tasks, as a longer working distance can be achieved than by proximal enlargement. Owing to the restricted fi eld of view, they are not normally suitable for use while mobile (Table 13.1).


Telescopes are essentially afocal systems, in which the rays of light entering the telescope from a distant object are parallel, as are the rays leaving the telescope and entering the user’s eyes. Two types of telescopes are used in low vision (Table 13.2):

• Astronomical telescopes (also known as Keplerian telescopes) consist of two convex (positive) lenses; the fi rst (Fo) converges the light so that the rays reverse when they pass the lenses focal length ( fo). The second eyepiece lens (Fe) converges the now divergent rays so that they are parallel when exiting the system (Fig. 13.1). The image is inverted, a situation that is rectifi ed, both laterally and vertically, by prisms. This can be

241

CHAPTER

TelescopesJames S. Wolffsohn

131313

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Table 13.1 Advantages and Disadvantages of Telescopes


Enlargement can be achieved at The fi eld of view is restricted witha longer working distance than the result that they are diffi cult ormost other forms of equivalent dangerous to use while mobilelow vision aid

Many can be focused to give both A dynamic target’s apparent speeddistance and near enlargement will be magnifi ed, as will its size

Can incorporate a patient’s Depth of fi eld required to maintainprescription or the telescope a clear image is reducedfocus can be adjusted

Generally expensive

Binocularity is diffi cult to achieve

Table 13.2 Relative Strengths and Weaknesses of Galilean and Astronomical Telescopes

Astronomical Galilean

Enlargement range 1.5–4.0× 2.0–10.0×

Lengtha Longer Shorter

Field of viewa Smaller Wider

Focusing rangea Greater Smaller

Image qualitya Better Poorer

Weighta Heavier Lighter

Complexity More complex Simpler

a Indicates comparison matched for enlargement.

Figure 13.1 Astronomical telescope optics.6

FE

FO

a

b

c

c

ab

fEfO´

t

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achieved using two right-angled (Porro) prisms, as in conventional binoculars; these also allow light paths to be folded, reducing the length of the telescope (Fig. 13.2). Inversion can also be achieved using fi ve-sided roof prisms, as incorporated into longer slim-line distance monoculars.

• Galilean telescopes also have a convex objective lens (Fo) to converge the light from the distant target, but a concave (negative) eyepiece lens (Fe). This is positioned closer than the focal length ( fo) of the objective lens, thereby diverging the converging light rays to exit the system in parallel. As can be seen from Figure 13.3, the image remains erect.

13.3 Telescope length

As can be seen from Figures 13.1 and 13.2:

t = fo + fe

where t is the telescope length, fo is the focal length of the objective lens FO, and fe is the focal length of the eyepiece lens FE.

Figure 13.2 Right-angled (Porro) prisms used to rectify the inverted astronomical telescope image and to fold the light path to reduce the telescope length. (Redrawn with permission from Dickinson 1998.6)

Figure 13.3 Galilean telescope optics. Redrawn with permission from Dickinson 1998.6

FO

FE

c

ab

FE

fE

fO´

FO

ta

b

c

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• For an astronomical telescope, both lenses are convex and therefore both fo and fe are positive, resulting in a longer system than a Galilean telescope that provides equivalent enlargement.

• For a Galilean telescope, the eyepiece lens is concave, and therefore fe is subtracted from fo.

To keep the length of the telescope practically short, the lenses must be as high powered as possible. However, the higher the power of the lenses, the greater the aberrations and the smaller the fi eld of view.

13.4 Telescope enlargement

Enlargement is defi ned by the size of the image divided by the size of the object (Fig. 13.4). As the size is dictated by the angular subtense:

Enlargement = Angle subtended by the image at the eye/angle subtended by the object at the eye

Figure 13.4 The ray path through an astronomical (A) and Galilean (B) telescope. Note that the exit pupil (EP) is within a Galilean telescope, but external to an astronomical telescope. (Redrawn with permission from Dickinson 1998.6)

FO

FO

FO

FO

FO´

FE

FE

FE

FO

FE´

fE´

fE´

fE´fO´

FE

h´

fO t

fO t

θ

EP

EP

θθ´

θ´

h´

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Regardless of whether the telescope is astronomical or Keplarian in design, as long as it is afocal:

Enlargement = −Fe/Fo

Therefore the eyepiece lens must be more powerful than the objec-tive lens to produce system enlargement.

Example 1

An astronomical telescope with an objective lens power of +20.00D and an eyepiece lens power of +40.00D.

t = fo + fet = +1/20 + +1/40Telescope length = 0.075 m = 7.5 cmEnlargement = −Fe/Fo

Enlargement = − +40/+20 = −2×

A Galilean telescope with an objective lens power of +20.00D and an eyepiece lens power of −40.00D.

t = fo + fet = +1/20 + −1/40Telescope length = 0.025 m = 2.5 cmEnlargement = −Fe/Fo

Enlargement = − −40/+20 = 2×

Taking into account enlargement and length considerations (see Section 13.3), astronomical telescopes consist of up to four components to minimise aberrations, giving up to 12× enlarge-ment. However, the increased number of optical interfaces causes a loss in image brightness and increases the weight of the telescope. Galilean systems are limited to 3× distance enlarge-ment, as image quality is generally unacceptable with greater enlargements.

13.5 Vergence of light

Emergent vergence of light from a telescope is described by:

U′ = M2U/(1 − tMU)

where t is the optical path length of the telescope, M is the enlarge-ment ratio of the telescope (positive for a Galilean and negative

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for an astronomical telescope), and U is the actual incidence vergence.

This formula can be simplifi ed to:1

U′ = M2U

Thus, if near objects are to be observed through a distance tele-scope, the accommodation required for a clear image is equal to the enlargement squared multiplied by the expected accommoda-tion. This also has implications for the depth of fi eld (maximum distance to which an object can be moved without inducing blur), which is greatly reduced in telescopes, making focus much more critical.

Example 2

A 6× telescope utilised for viewing an object at 66 cm.

U′ = M2UU = 1/0.66 = 1.5D accommodation expected = 62 × 1.5 = 54.0D of accommodation required

13.6 Compensating for refractive error

Refractive error can be practically compensated for in telescope viewing by:

• Adding the full refractive correction to the eyepiece (or alternatively encouraging the patient to view through their glasses) – the enlargement of the telescope remains unchanged as it is still afocal, and astigmatism can be compensated for as well as spherical refractive error.

• Altering the telescope’s length – myopes can shorten a telescope, altering the emergent light from parallel to divergent, resulting in less enlargement if using a Galilean telescope and greater enlargement if using an astronomical telescope (see Example 3). Conversely, a hypermetrope can lengthen a telescope, altering the emergent light from parallel to convergent, resulting in less enlargement if using an

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astronomical telescope and greater enlargement if using a Galilean telescope.

Example 3

An astronomical telescope with an objective lens power of +20.00D and an eyepiece lens power of +40.00D utilised by an uncorrected −6.00D myope.

As shown in Example 1, this afocal telescope used by an emmetrope would have a length of 7.5 cm and enlargement of −2×. As this telescope is now used by a myope, the eyepiece lens can be thought of as a −6.00D lens to correct the refractive error and a +46.00D eyepiece of an afocal telescope.

t = fo + fet = +1/20 + +1/46Telescope length = 0.072 m = 7.2 cm (i.e. a shortening of 3 mm)Enlargement = −Fe/Fo

Enlargement = − +46/+20 = −2.3×

A Galilean telescope with an objective lens power of +20.00D and an eyepiece lens power of −40.00D utilised by an uncorrected −6.00D myope.

As shown in Example 1, this afocal telescope used by an emmetrope would have a length of 2.5 cm and enlargement of 2×. As this telescope is now used by a myope, the eyepiece lens can be thought of as a −6.00D lens to correct the refractive error and a −34.00D eyepiece of an afocal telescope.

t = fo + fet = +1/20 + −1/34Telescope length = 0.021 m = 2.1 cm (i.e. a shortening of 4 mm)Enlargement = −Fe/Fo

Enlargement = − −34/+20 = 1.7×

In theory, a partial refractive correction could be placed over the objective lens to change the vergence of light entering the eye, which is then amplifi ed (see Section 13.5) to correct the full refrac-tive error. However, the power of correction required and its effect on magnifi cation would be diffi cult to calculate.

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13.7 Telescope viewing of non-distant objects

As demonstrated in Example 2, the accommodative demands for viewing a near object through an afocal telescope are greatly amplifi ed. Viewing of non-distant objects through a telescope can be practically achieved by:

1 Adding a correction to the eyepiece lens – because the divergent light from the object is amplifi ed as it passes through the telescope, a very strong positive lens would need to be placed over the eyepiece or worn. This is practical only when a patient already uses a high-powered spectacle magnifi er (see Ch. 12) for near viewing, in which case using this together with an afocal telescope will increase the working distance.

2 Altering the telescope’s length – increasing the length of a telescope allows nearer objects to be viewed clearly. The limit is dependent on the tube length of the telescope, so generally astronomical telescopes allow a greater range of focus than Galilean telescopes. In addition, astronomical telescopes typically make use of higher powered components than Galilean telescopes, to keep the telescope length short. As the lengthening of the telescope can be considered to have affected the objective lens, and this is convex in both types of telescope, the length and enlargement are altered by the same amount.

Example 4

An astronomical telescope with an objective lens power of +20.00D and an eyepiece lens power of +40.00D utilised to view an object at 50 cm.

As shown in Example 1, this afocal telescope would have a length of 7.5 cm and enlargement of −2×. As this telescope is now used to view an object at 50 cm, the objective lens can be thought of as a +2.00D lens to correct for the working distance and a +18.00D objective of an afocal telescope.

t = fo + fet = +1/18 + +1/40Telescope length = 0.081 m = 8.1 cm (i.e. a lengthening of 6 mm)Enlargement = −Fe/Fo

Enlargement = − +40/+18 = −2.2×

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A Galilean telescope with an objective lens power of +20.00D and an eyepiece lens power of −40.00D utilised to view an object at 50 cm.

As shown in Example 1, this afocal telescope used by an emmetrope would have a length of 2.5 cm and enlargement of 2×. As this telescope is now used to view an object at 50 cm, the objective lens can be thought of as a +2.00D lens to correct for the working distance and a +18.00D objective of an afocal telescope.

t = fo + fet = +1/18 + −1/40Telescope length = 0.031 m = 3.1 cm (i.e. a lengthening of 6 mm)Enlargement = −Fe/Fo

Enlargement = − −40/+18 = 2.2×

3 Adding a lens cap to the objective lens – by neutralising the divergence of the object’s working distance (e.g. a +3.00D lens cap for an object at 33 cm), the telescope remains afocal. A telescope with the addition of a reading cap is known as a telemicroscope. The enlargement of the system is the product of its individual components, so:

Enlargement (E) = Etelescope × (lens cap power/4)

Various combinations of telescope enlargement and lens cap can be used to give a particular system enlargement, each with a working distance dependent on the lens cap power.

Example 5

An astronomical telescope with an objective lens power of +20.00D and an eyepiece lens power of +40.00D with lens cap of +2.00D utilised to view an object at 50 cm.

Practical advice

If the working distance is greater than 25 cm, requiring a lens cap power of less than 4.00D, the resulting telemicroscope will have a reduced enlargement compared with the telescope utilised.

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The telescope remains afocal, so has the same length and enlargement as shown in Example 1.

Enlargement (E) = Etelescope × (lens cap power/4) = 2 × (2/4) = 1×Working distance = 1/lens cap power = 0.50 m

To achieve unit (1×) enlargement with a plus lens addition alone would require a +4.00D lens (Enlargement = lens power/4 = +4/4 = 1×).

Working distance = 1/lens power = 0.25 m

Note: A telemicroscope will always allow a longer working distance (WD) for the same enlargement as a plus lens addition, such that:

WDtelemicroscope = Etelescope × WDplus lens addition

The length of the telescope is also greater than a plus lens addition, so the working distance from the eye is still further increased.

It is always better to refocus a telescope (if practical) than to add a reading cap over the objective as the enlargement is increased. The greater working distance also allows binocularity for near tasks with higher levels of enlargement (up to about 5×) than with spec-tacle magnifi ers (which are limited to approximately 2.5×), although the telescope tubes may need to be converged and the interpupil-lary distance altered to compensate for the eye convergence.

13.8 Exit pupil

As can be seen from Figures 13.1 and 13.3, the exit pupil is smaller than the objective lens (which limits the light rays entering the telescope), such that:

Exit pupil diameter = objective lens diameter/telescope enlargement

The exit pupil of a Galilean telescope is within the telescope, unlike that of an astronomical telescope (see Fig. 13.4). This means that more careful alignment is required to maintain as large a fi eld of view as possible. Therefore, if the telescope eyepiece is held still at about 20 cm from the observer pointing towards a light area,

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the exit pupil can be seen as a bright circle of light, moving in the same direction as the observer’s head for a Galilean telescope and in the opposite direction for an astronomical telescope (Fig. 13.5).

Figure 13.5 Telescope exit pupil. If the telescope eyepiece is viewed end on and the exit pupil appears to move in the same direction as the head (‘with’ movement), this indicates that the telescope is Galilean (exit pupil within the telescope), whereas movement of the exit pupil in the opposite direction to the head (‘against’ movement) indicates the telescope is astronomical. To measure the exit pupil, a ruler or band magnifi er is held as close as possible to the exit pupil (against the eyepiece for a Galilean telescope, as the exit pupil is within the telescope).

13.9 Field of view

Field of view is normally determined by the objective lens diame-ter. Telescopes are traditionally labelled as ‘enlargement’ times ‘objective lens diameter’ in millimetres (e.g. 4 × 16, in which case the exit pupil would be 4 mm). To achieve the maximum fi eld of view, the eye should be touching the eyepiece lens and the pupil diameter should match the exit pupil. This is impossible to achieve

Practical advice

The design of a telescope can be determined from the movement of the exit pupil when the telescope is held still and the observer’s head is moved. A long telescope length and observable prisms within the telescope may indicate the telescope to be of astronomical design. As the lenses within the telescope may be compound to minimise aberrations, the shape or back surface curvature of the fi nal eyepiece lens may not dictate the telescope design.

Exit pupil

Head movement Head movement

Apparent ‘with’movement with a

Galilean telescope

Apparent ‘against’movement with an

astronomical telescope

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in a Galilean telescope when the exit pupil is virtual and inside the system (see Fig. 13.4). Increasing the distance between the eye and the exit pupil will decrease the fi eld of view. Despite the loss of some peripheral rays of light, an exit pupil slightly larger than the observer’s pupil is preferred, so that small amounts of mis-alignment do not cause fi eld loss (seen as dark crescent-type areas at the periphery of the fi eld of view). The fi eld of view (in distance terms) increases in proportion to the working distance of the object being viewed (Fig. 13.6).

13.10 Measuring telescope enlargement

Although several methods are available to determine the enlarge-ment of a telescope, the most practical are:

• Direct comparison – an estimation of the magnifi ed view compared with the view without the telescope. This is best achieved by viewing a regular pattern (such as a brick wall) simultaneously through both eyes, with the telescope in front of one (Fig. 13.7). This can be diffi cult to master initially; the person essentially has to disassociate their binocularity, but with practice it can be achieved effectively.

• Measurement of objective lens and exit pupil – as described in Section 13.8, the exit pupil can be viewed and measured. The objective lens can be measured easily, although its diameter is also often stated on the telescope:

Enlargement = diameter of objective lens/exit pupil diameter

For a telemicroscope, determine the anterior focal length of the lens cap (1/working distance), place a lens of equal and opposite

Figure 13.6 Relative fi eld of view with telescope to object distance.

The field ofview is verylimited upclose to thetelescope,butimproves asthe object ismovedfurther awayfrom the

The field ofview is verylimited upclose to thetelescope,butimproves asthe object ismovedfurther awayfrom the

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power in contact with the telescope objective lens, and determine the power as described above (see Section 13.7).

13.11 Telescopes designed for mobility

It was noted in Section 13.1 that, owing to the restricted fi eld of view, telescopes are not normally suitable for use while on the move. However, several designs have attempted to overcome this limitation:

• Bioptic telescopes – typically present a magnifi ed retinal image, but only to part of the fi eld of view. Hence, the user views through their refractive correction, utilising the image enhancement through the compact low-powered telescope, by a change in head/eye position as required.2 Bioptic telescopes can be used for driving in many states of the USA, although they cause a ring scotoma around the magnifi ed zone (Fig. 13.8) (see Ch. 7).

• Autofocus telescopes – lightweight autofocus is available on some designs of telescope to allow users to track objects more easily at changing distances. If the system is binocular, convergence

Figure 13.7 Viewing of a regular pattern with and without a telescope to estimate enlargement.

Figure 13.8 Autofocus bioptic telescope (Ocutech Vision Enhancement System). (Courtesy of Dr Robert Harper.)

Naked eye 4x telescopeview

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of the telescope tubes will also have to be motorised, and this can prove technically challenging. A randomised cross-over trial has shown that an improved vision-related quality of life is measurable in visually impaired patients who are prescribed an autofocus bioptic telescope, compared with traditional telescopes and other low vision aids.5

• Contact lens and spectacle lens combination telescopes – the fi eld of view of a telescope can be increased by decreasing the distance between the objective lens and the eye. Hence fi tting the eye with a negative powered contact lens (typically about −30.00D) in combination with a positive powered spectacle lens creates a Galilean telescope with a length equal to the back vertex distance of the spectacles. The fi eld of view is dependent on the power, diameter and vertex distance of the spectacle lens. A ring scotoma around the lens edge can be minimised by using a blended aspheric lens. As the vertex distance is limited in practice (together with a decreased fi eld of view as this is increased), the maximum enlargement that can be achieved is 1.8–2.0×.3 Owing to the vergence amplifi cation through the telescope, stronger reading additions/accommodation will be needed for viewing near objects. The use of an intraocular lens has also been attempted in place of the contact lens, achieving a greater enlargement.4 Practical success with these systems has, however, been less than initially anticipated.

13.12 Aids for peripheral fi eld loss

Field loss, particularly if less than 20º of the visual fi eld remains, can cause severe visual impairment. Pathologies such as retinitis pigmentosa and end-stage glaucoma can severely constrict the visual fi eld, and stroke or other brain injuries can cause hemiano-pic fi eld loss. Aids for visual fi eld loss are:

• Reversed telescopes – these increase the fi eld of view (although in commercial designs this is limited by the now smaller objective lens) at the expense of visual acuity. The depth of focus is, of course, increased dramatically. Door peer-hole viewers can be used as an economic hand-held device.

• Negatively powered lens – held 20–30 cm from the eye, this lens acts as the objective of a reversed Galilean telescope with the patient’s accommodation as the eyepiece.

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• Spectacle refl ecting systems – an alternative to telescopic systems, typically used in hemianopic fi eld loss, can reduce the eye or head movement needed to scan the visual environment. The options are:• a mirror in front of the seeing fi eld to refl ect objects in the

non-seeing area into the seeing fi eld, but at the expense of fi eld of view and the movement in the mirror is reversed. Mirrors attached to the rear of spectacles are more discrete, but have to be smaller and hence have a smaller fi eld of view.

• a right-angled prism, base towards the fi eld defect in front of the non-seeing fi eld. This refracts the image from more peripheral objects closer to the visual angle, but causes image jump when the visual axis meets the edge of the prism. Frenel prisms can be used in various shapes and locations on the spectacle lenses to achieve an optimum effect for the patient.

13.13 Summary

• Telescopes used in low vision are either Galilean or astronomical in design.

• They may be monocular or binocular, hand-held or mounted/clipped on to spectacles (Fig. 13.9).

• They allow enlargement at greater working distances than most other forms of low vision aid, but have a limited fi eld of view.


• Although telescopes can be used to watch television, moving closer can achieve a similar effect with an unrestricted fi eld of view and without having to support the telescope (e.g. 3× enlargement can be created by using a 3× telescope to view a television at 3 m, or the observer can move to 1 m).

• Telemicroscopes offer a longer working distance for near tasks than plus lens additions, but at the compromise of a reduced fi eld of view.

• To check the alignment of a telescope for binocular viewing, stand at the desired distance from the observer and monocularly check that the telescope tubes appear concentric with each other and the observer’s pupils.

• Training should always be provided when prescribing a telescope. This should include:

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• how to hold the telescope, what eye to use and whether glasses need to be worn

• focusing and maximising the fi eld of view• steadying the telescope using the eye orbit and keeping the

elbows in• practising spotting (localisation and focusing), tracing (e.g.

around an object), tracking (e.g. a moving bus) and scanning (searching for an object).

References

1. Garnier B, Colonna Da Lega X. Low-vision aid using a high-minus intraocular lens. Applied Optics 1992; 31:3632–3636.

2. Fried AN. Telescopes, light vergence and accommodation. American Journal of Optometry and Physiological Optics 1977; 54:365–373.

3. Korb DR. Preparing the visually handicapped person for motor vehicle operation. American Journal of Optometry and Archives of the American Adacemy of Optometry 1970; 47:619–628.

4. Harper RA, Chandler C, Reeves BC, Sznapka J, Dickinson CM. A randomised cross-over trial to assess vision-related quality of life with an autofocus bioptic telescope. Ophthalmic Research 2005; 37:S77.

5. Lewis HT. Parameters of contact lens–spectacle telescopic systems and considerations in prescribing. American Journal of Optometry and Physiological Optics 1986; 63:387–391.

6. Dickinson C. Low vision: principles and practice. Oxford: Butterworth-Heinemann; 1998.

Figure 13.9 A range of telescopes.

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14.1 Classifi cation and defi nition

The broad range of electronic vision enhancement systems (EVES) currently on the market has resulted from general consumer demand for the individual components (video cameras and display screens) and the simplicity of connecting them together (Fig. 14.1 [Plate 15]). As a result, many of the companies selling EVES do not have a strong interest or background in low vision rehabilitation. Although attempts have been made to classify EVES in terms of performance attributes, such as portability, ease of operation and aesthetic appearance,1 these are diffi cult to quantify objectively. Many systems have more than one option of viewing display and image enhancement features. It is therefore suggested that EVES are classifi ed as outlined in Figure 14.2.2

EVES are often referred to as closed-circuit televisions (CCTVs), because of the direct cable link between the camera imag-ing system and the monitor viewing system (in contrast to broadcast television), but this description generally refers to surveillance devices and does not indicate the provision of fea-tures, such as enlargement and contrast enhancement, found in devices for the visually impaired. The term ‘electronic vision enhancement systems (EVES)’ better distinguishes and describes such devices.

257

CHAPTER

Electronic vision enhancement systemsJames S. Wolffsohn

141414

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14.2 EVES: advantages and disadvantages

Electronic devices that provide electronic (transverse) enlargement were introduced in the early 1970s, although the concept was fi rst described by Potts et al3 in 1959. In 1969, Genensky4 went on to describe modifi cations such as variable magnifi cation, self-focus-ing, reverse contrast, high-speed line return and a Gestalt system (to allow a wider fi eld of view, with a small area of interest magni-fi ed). Advantages and disadvantages are listed in Table 14.1.

14.2.1 ‘Mouse’-style devices

‘Mouse’-style, more portable, EVES were fi rst described in the 1970s.5,6 They consist of a camera usually mounted on rollers in a small hand-held case that can be moved over the object of interest (Fig. 14.3). They encompass features common to more traditional stand-based EVES (Fig. 14.4), such as contrast reversal and variable magnifi cation (although the range is usually limited), and they may be self-focusing. Mouse-style devices are more portable than con-ventional stand-based EVES, but battery power options tend to be heavy and expensive, and they need to be connected to a television

Figure 14.1 (Plate 15) A range of EVES.

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14Electronic vision enhancement systems 1414

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set or monitor. Early-model mouse EVES required a fairly fl at surface to be rolled over for good image clarity; tasks such as writing could not be performed beneath them and patients often had diffi culty maintaining their spatial awareness of the text layout.7 Newer models have a larger depth of focus, enabling curved sur-faces to be viewed, and they can, in addition, be mounted on a stand or tilted on edge to enable the user to write beneath the camera. Viewing monitors are often integrated in newer versions, but have a limited fi eld of view due to size and weight constrictions.

Figure 14.2 Classifi cation of presently available EVES. CRT, cathode ray tube; LCD, liquid crystal display; TFT, thin-fi lm transistor.

Camera

Display

Power

Colour Black and white

Stand mounted Mouse with rollers Hand held Head mounted

Type

LCD TFT

Foreground/backgroundcolour options

Contrast/luminanceenhancing

Contrastreversal

Magnificationrange

In-line(fixed)

Side by side(variable)

Head mounted(HMD)

CRT

Size Electronicfeatures

Position cf.camera

Mains Battery

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Table 14.1 Advantages and Disadvantages of EVES


Large range of enlargement, much Generally expensivegreater than optical low vision aids(LVAs) and variable if condition worsens8

Simple image manipulation (such Users tend to adopt inappropriateas reversing the image contrast) ergonomic layouts, resulting inpossible neck and back aches,9 especially if bifocals are worn10

Can be used at natural workingdistances, binocularly and with good posture

Minimal peripheral aberrations, lesscritical focus and reduced light loss compared with optical LVAs

Figure 14.3 ‘Mouse’-type EVES.

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14.2.2 Head-mounted devices

Head-mounted video magnifi cation devices allow greater porta-bility and usage for a wider variety of tasks.11 Video screens are viewed through highly powered positive lenses, which enable the user to focus the screen at a greatly reduced distance, thereby allowing a relatively large fi eld of view. The advent of miniature solid-state electronics has enabled the production of more portable and cheaper electronic magnifi cation aids12 that can be attached to a head-mounted system, such as the low vision image system (LVIS) or low vision enhancement system (LVES). The use of such devices can improve both visual acuity (up to 10-fold) and contrast sensitivity (by up to 1.8 log units), without affecting reading speed or comprehension (Fig. 14.5).13,14 These devices can be time con-

Figure 14.4 Stand-based EVES.

Practical advice

‘Mouse’-style EVES are generally cheaper than conventional ‘stand’-based EVES. Costs can be reduced further, as many can be plugged into the patient’s own television or monitor.

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suming to fi t, can cause problems with claustrophobia and motion sickness, and the user requires steady head and hand control if the system is to be used effectively. Head-mounted display viewing can also decrease task performance compared with magnifi cation and fi eld of view-matched monitor viewing.15

Another important issue is the adequacy of retinal stabilisation during head movements, as at velocities of greater than 20 degrees per second (typical of those experienced when walking) dynamic visual acuity is decreased regardless of the magnifi cation.11 There-fore, it has been suggested that presently available head-mounted low vision systems are suitable for only a small number of patients who are highly motivated and mentally alert.11

14.2.3 Comparison of devices

Several studies have compared different types of EVES to optical LVAs.13,15–21 The main fi ndings have been that EVES allow reading

Figure 14.5 Head-mounted EVES. (From Broadbent J, Culham L. Prescribing conventional devices for vision rehabilitation. CE Optometry 2002; 5(1), 12–16, with permission from Rila Publications Ltd, London.)

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to be faster and of longer duration than is possible with optical LVAs. Smaller print sizes can also be read. For a basic reading task, no differences in reading speed between a mouse and stand-based EVES have been found.7,15,21 However, head-mounted viewing reduces reading speed, and some tasks are faster to perform with an optical LVA than with EVES, particularly when undertaken by young visually impaired persons.15,22

14.3 EVES users and usage

The majority of EVES users are young and highly motivated, although children are less likely than adults to use their EVES regularly.9,10 Unfortunately the cost of EVES has excluded them from being commonly prescribed, with reported EVES prescribing in non-Veterans’ Affairs low vision clinics ranging from approxi-mately 1.7%23 to 25%,24 being highly dependent on funding issues. EVES may be purchased by government departments or charitable organisations for certain needy individuals. In the UK, EVES used to be prescribed, if ‘essential to employment’, under the Manpower Services Commission Scheme,22 but this now occurs through the ‘access to work’ scheme, which is part of Employment Services (a government agency). Children usually obtain EVES through the educational authority after formal assessment by suitably trained individuals.

The main use of EVES has been to assist the visually impaired with reading. Other uses include dealing with correspondence, school tasks, fi lling in forms, writing and viewing photographs.9,16,25 EVES can also be used for more individual tasks such as performing a hobby, with 42% using their EVES for tasks other than those they had originally intended.26,27 Newer head-mounted systems can be used for a range of different tasks including reading, watching tele-vision, computing, sight-seeing, typing, writing and doing repairs.11

Follow-up of patients prescribed EVES by Veterans’ Affairs in the USA, after approximately 2 years, has indicated that 85–90% of them still use their EVES, fi nd them benefi cial and demonstrate effi cient use of the device.8,26,27 Age, acuity and aetiology of visual impairment have been found to be unrelated to continued use of EVES.26,27 Interestingly, those with a distance visual acuity better than 6/90 (approximately 1.2 LogMAR) have been found to gain little benefi t from using EVES, many having higher reading speeds with their optical LVA.10

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14.5 Reading speed and fi eld of view

As the viewing screen size is fi xed, increases in magnifi cation decrease the fi eld of view and, importantly, the number of letters or words that can be seen at any one time (Fig. 14.6). Increments in magnifi cation enable an initial increase in reading speed up to a maximum, followed by a plateau or decrease with further increases (see Ch. 7).13,17 The window size (fi eld of view) require-ment for reading (with page navigation) using EVES has been found to be 10 characters for 85% of maximum reading speed, but more than 20 characters for maximum reading speed to be achieved.28 Research has suggested that visual factors (decoding) rather than navigational demands constrain reading speed in those with visual impairment.7,28

14.4 Enlargement

As with all magnifi cation aids, the necessary level of enlargement can be predicted (see Ch. 9), although EVES allow the user to modify this level depending on personal preference and the task being undertaken. In general, self-selection of enlargement will tend to be greater than that of optical LVAs used by the patient.18

Enlargement is the measured increase in size of the image on the EVES monitor with respect to the real image (object) size. Moving the patient closer to the monitor produces relative dis-tance (proximal) enlargement (see Section 9.4.1). This type of enlargement does not affect the patient’s equivalent fi eld of view and may be facilitated by myopia, accommodation or a higher reading addition. However, studies indicate that working dis-tances used with stand EVES are generally consistently chosen to be about 40 cm and are always less than 1 m.7,8 Not one patient, in a large survey of EVES users, was found to employ special focus glasses for EVES use.9

Practical advice

To measure the chosen enlargement of an EVES, divide the width of the object image on the screen by the width of the true object underneath the camera.

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The distance of the eye from the borders of the display fi eld is further than from its centre, an effect exaggerated by the slight overall convexity of cathode ray tubes.29 Thin-fi lm transistor and liquid crystal displays are fl atter and, owing to their thin profi le, more functional ergonomically. Screen resolution is unlikely to be a limiting factor for the visually impaired, but a larger screen size results in a greater fi eld of view for the same enlargement on a smaller screen.

Figure 14.6 Example of the limited fi eld of view achieved through an EVES providing high enlargement.

Practical advice

The visually impaired should be assisted in setting enlargement levels of EVES so that reading speed is maximised. Ideally at least 10 to 20 characters should fi t within the screen width at the chosen magnifi cation.

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14.6 Duration of reading

The visually impaired can generally read for longer with EVES than with spectacle lenses or conventional LVAs, but use a higher level of magnifi cation.18 The average reading duration using EVES has been found to be about 2 hours, compared with just 30 minutes with optical LVAs – with dry eyes and headaches given as the main reasons for cessation of reading.8,25–27 The average duration of use at one sitting decreases with advancing age.9

14.7 Contrast

Reading performance with EVES is related more to contrast sen-sitivity than to distance or near visual acuity.8,30 If contrast is maximised, the magnifi cation of the print can be reduced while retaining equivalent reading performance.30 For example, reduc-ing the contrast of the text by approximately 40% reduces reading rate by about 25%. Although some EVES feature the ability to display monochrome images in contrasting colours (such as white, green and amber), there appears to be no scientifi c basis to this approach apart from some EVES users having a subjective preference.31,32

The blur perceived when EVES are used while moving black-on-white print (owing to the update rate) is increased by reversed-contrast white-on-black print. However, this disadvan-tage of using reversed-contrast print must be weighed against the advantages of reduced glare and less picture fl icker than when using black-on-white print.9 Preference for reversed-contrast print over black-on-white print seems to be on an indi-vidual basis, perhaps infl uenced by the condition causing visual impairment.16,22

Practical advice

Contrast reversal should be demonstrated to all potential EVES users, and contrast should be maximised to reduce the required magnifi cation level.

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14.8 Image enhancement

Image processing can enhance the visibility of text for patients with low vision, although only if based on the individual’s loss in visual function.33–35 Digital imaging can be used to add contrast, luminance or coloured fi lters, and to magnify, compress or relocate selected parts of the image to create user-specifi c images. This is not possible with conventional lenses, mirrors and prisms.36 Research on image enhancement of television-type images and face recognition has suggested that moderate benefi t to the visu-ally impaired can be achieved with both patient-specifi c and generic fi lters.35,37,38 However, most of these studies have been based on preferences to static rather than true dynamic television images.

To date, EVES allow minimal (mainly global contrast) image enhancement, although a recent embodiment (myReader, Pulse Data International) captures text electronically and can present it to users in their preferred format.35 Head-mounted luminance enhancement systems (similar to night vision goggles) have been shown to improve visual performance in terms of visual acuity, contrast sensitivity, motion contrast, mobility and orientation in visually impaired patients with night blindness from conditions such as retinitis pigmentosa.39,40

14.9 Training

Reading speed and duration have been found to increase in the visually impaired with intensive EVES training in some studies.41,42 However, other studies have found reading speed and task per-formance to be no different between (age and sex matched) visu-ally impaired novice and experienced EVES users,15 and reading speed and comprehension was not improved with practice in novice head-mounted EVES users.13 There is also no evidence to indicate which components of training are necessary, benefi cial and actively increase the effi cacy of EVES usage. For those studies that have shown an improvement in EVES usage with training (over a period of between a few days and several months), the results do not appear to be related to the patient’s age, visual acuity or level of education.41,42

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Training programmes usually orient the patient with the EVES physical arrangement; operation of the monitor and camera, such as the enlargement of print size; and ability to track with the X–Y table, to eliminate unnecessary movements. Manual dexterity task training is needed for EVES usage and a hierarchy of increas-ingly diffi cult tasks has been suggested as the basis for a training scheme. In addition, teaching to think in units rather than single words, and to learn skimming and previewing skills, may be benefi cial.42–44

14.10 Summary

• Electronic vision enhancement system is a more appropriate term than closed-circuit television (CCTV).

• EVES have many benefi ts over optical aids, such as allowing greater levels of enlargement, contrast enhancement and a more natural working distance.

• ‘Mouse’ cameras and head-mounted displays increase the portability of EVES, although they can adversely affect task performance over traditional ‘stand’ EVES.

• EVES generally allow a longer reading duration than optical LVAs, although some visually impaired patients have faster task performance with optical aids.


• EVES are worth considering for anyone who is in education or employment, particularly if they have a progressive sight loss condition. Relatively inexpensive options are available.

• It is better to demonstrate EVES to a patient and discuss the advantages and disadvantages with them than to presume (often wrongly) that they cannot afford one. With greater access to information through support groups and the internet, patients are likely to question whether EVES would be of benefi t to them at some point – and perhaps purchase a system without expert guidance.

• Always calculate the enlargement required for a patient to carry out a particular task and demonstrate how further enlargement can reduce rather than enhance performance.

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References

1. Strong JG, Byard A. Protocols for the prescribing of non-generic closed-circuit television (CCTV) systems for individuals with low vision. Investigative Ophthalmology and Visual Science 1992; 33:S1417.

2. Wolffsohn JS, Peterson RC. Current knowledge on electronic vision enhancement systems (EVES) for the visually impaired. Ophthalmic and Physiological Optics 2003; 23:35–42.

3. Potts AM, Volk D, West SS. A television reader as a subnormal vision aid. American Journal of Ophthalmology 1959; 47:580–581.

4. Genensky SM. Some comments on a closed circuit TV system for the visually handicapped. American Journal of Optometry and Archives of American Academy of Optometry 1969; 46:519–524.

5. Laviere M, Wilson GB. A portable closed-circuit television aid for the partially sighted. American Journal of Optometry and Archives of the American Academy of Optometry 1972; 49:178–179.

6. Fletcher R. Evaluation of a CCTV device for partial sight. British Journal of Physiological Optics 1979; 33:11–18.

7. Harland S, Legge GE, Luebker A. Psychophysics of reading. XVII. Low-vision performance with four types of electronically magnifi ed text. Optometry and Visual Science 1998; 75:183–190.

8. Goodrich GL, Mehr EB, Darling NC. Parameters in the use of CCTVs and optical aids. American Journal of Optometry and Physiological Optics 1980: 57:881–892.

9. Zabel L, Bouma H, Melotte HEM. Use of the TV magnifi er in the Netherlands: a survey. Journal of Visual Impairment and Blindness 1982; 86:25–29.

10. Fonda GE, Thomas H, Schnur RN. Evaluation of closed-circuit television as an optical aid for the low-vision patient. Transactions. Section on Ophthalmology. American Academy of Ophthalmology and Otolaryngology 1975; 79:OP468–482.

11. Harper R, Culham L, Dickinson C. Head mounted video magnifi cation devices for low vision rehabilitation: a comparison with existing technology. British Journal of Ophthalmology 1999; 83:495–500.

12. Fowler C. Simplifi ed closed circuit television magnifi er for the partially sighted. Ophthalmic and Physiological Optics 1993; 13:95–96.

13. Ortiz A, Chung STL, Legge GE, Jobling JT. Reading with a head-mounted video magnifi er. Optometry and Visual Science 1999; 76:755–763.

14. Ballinger R, Lalle P, Maino J, Stelmack J, Tallman K, Wacker R. Veterans’ Affairs multicenter low vision enhancement system (LVES) study: clinical results. Report 1: Effects of manual-focus

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LVES on visual acuity and contrast sensitivity. Optometry 2000; 71:764–774.

15. Peterson RC, Wolffsohn JS, Rubinstein M, Lowe J. Benefi ts of electronic vision enhancement systems (EVES) for the visually impaired. American Journal of Ophthalmology 2003; 136:1129–1135.

16. Mehr EB, Frost AB, Apple LE. Experience with closed circuit television in the blind rehabilitation program of the Veterans’ Administration. American Journal of Optometry and Archives of the American Academy of Optometry 1973; 50:458–469.

17. Lovie-Kitchin JE, Woo GC. Effect of magnifi cation and fi eld of view on reading speed using a CCTV. Ophthalmic and Physiological Optics 1988; 8:139–145.

18. Stelmack J, Reda D, Ahlers S, Bainbridge L, McCray J. Reading performance of geriatric patients post exudative maculopathy. Journal of the American Optometric Association 1991; 62:53–57.

19. Harland S, Legge GE, Luebker A. Psychophysics of reading. XVII. Low-vision performance with four types of electronically magnifi ed text. Optometry and Visual Science 1999;75:183–190.

20. Fujita K, Arai M, Cheng HM et al. Reading with a portable closed-circuit television (CCTV) for patients with age-related macular degeneration (AMD). Investigative Ophthalmology and Visual Science 2001; 42:4286.

21. Goodrich GL, Kirby J. A comparison of patient performance and preference: optical devices, handheld CCTV (Innovations Magni-Cam), or stand mounted CCTV (Optelec Clearview or TSI Genie). Optometry 2001; 72:519–528.

22. Ehrlich D. A comparative study in the use of closed-circuit television reading machines and optical aids by patients with retinitis pigmentosa and maculopathy. Ophthalmic and Physiological Optics 1987; 7:293–302.

23. Wolffsohn JS, Cochrane AL. The changing face of the visually impaired. The Kooyong low vision clinic’s past, present and future. Optometry and Visual Science 1999; 76:747–754.

24. Rohrschneider K, Bruder I, Blankenagel A. Ophthalmological rehabilitation – experience at the University Eye Hospital Heidelberg. Ophthalmologe 1999; 96:611–616.

25. Goodrich GL, Apple LE, Frost A, Wood A, Ward R, Darling N. A preliminary report on experienced closed-circuit television users. American Journal of Optometry and Physiological Optics 1976; 53:7–15.

26. Watson GR, De L’Aune W, Stelmack J, Maino J, Long S. National survey of the impact of low vision device use among veterans. Optometry and Visual Science 1997; 74:249–259.

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27. Watson GR, De L’Aune W, Long S, Maino J, Stelmack J. Veterans’ use of low vision devices for reading. Optometry and Visual Science 1997; 74:260–265.

28. Beckmann PJ, Legge GE. Psychophysics of reading – XIV. The page navigation problem in using magnifi ers. Vision Research 1996; 36:3723–3733.

29. Lowe JB, Drasdo N. Effi ciency in reading with closed-circuit television for low vision. Ophthalmic and Physiological Optics 1990; 10:225–233.

30. Brown B. Reading performance in low vision patients: relation to contrast and contrast sensitivity. American Journal of Optometry and Physiological Optics 1981; 58:218–226.

31. Legge GE, Rubin GS. Psychophysics of reading. IV. Wavelength effects in normal and low vision. Journal of the Optical Society of America 1986; 3:40–51.

32. Jacobs RJ. Screen color and reading performance on closed-circuit television. Journal of Visual Impairment and Blindness 1990; 84:569–572.

33. Fine EM, Peli E, Pisano K. Contrast enhancement does not appreciably increase the reading rate of scrolled text. Investigative Ophthalmology and Visual Science 1993; 33:S789.

34. Lawton TA, Sebag J, Sadun AA, Castleman KR. Image enhancement improves reading performance in age-related macular degeneration patients. Vision Research 1997; 38:153–162.

35. Peli E, Kim J, Yitzhaky Y, Goldstein RB, Woods RL. Wideband enhancement of television images for people with visual impairments. Journal of the Optical Society of America. A, Optics, Image Science, and Vision 2004; 21:937–950.

36. Loshin DS, Juday RD. The programmable remapper: clinical applications for patients with fi eld defects. Optometry and Visual Science 1989; 66:389–395.

37. Tang J, Kim J, Peli E. Image enhancement in the JPEG domain for people with vision impairment. IEEE Transactions on Bio-medical Engineering 2004; 51:2013–2023.

38. Leat SJ, Omoruyi G, Kennedy A, Jernigan E. Generic and customised digital image enhancement fi lters for the visually impaired. Vision Research 2005; 45:1991–2007.

39. Friedburg C, Serey L, Sharpe LT, Trauzettel-Klosinski S, Zrenner E. Evaluation of the night vision spectacles on patients with impaired night vision. Graefe’s Archive for Clinical and Experimental Ophthalmology 1999; 237:125–136.

40. Spandau UHM, Wechsler S, Blankenagel A. Testing night vision goggles in a dark outside environment. Optometry and Visual Science 2002; 79:39–45.

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41. Goodrich GL, Mehr EB, Quillman RD, Shaw HK, Wiley JK. Training and practice effects in performance with low-vision aids: a preliminary study. American Journal of Optometry and Physiological Optics 1977; 54:312–318.

42. Lagrow SJ. CCTV reading rates of visually impaired students. Journal of Visual Impairment and Blindness 1981; 75:368–373.

43. Faubert J, Overbury O. Active–passive paradigm in assessing CCTV aided reading. American Journal of Optometry and Physiological Optics 1987; 64:23–28.

44. Lund R, Watson GR. The CCTV book: habilitation and rehabilitation with CCTV systems. Frolund, Norway: Synsforum ans; 1997.

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15.1 Classifi cation and defi nition

Optical aids are often prescribed for those with low vision. However, there is a wide range of non-optical and sensorial aids that can assist those with visual impairment to function better and have a higher quality of life. Non-optical aids assist the visually impaired user either to maximise their residual visual potential or to make use of a different output signal in order to stimulate one of the other senses (such as touch or hearing). Many aids are designed in such a way that they both assist vision and provide additional sensory output. Appliances can be classifi ed according to whether they provide one or more of the following features:

1 Enlarged characters (see Ch. 9), as in large print books and clocks, watches and syringes.

2 Increased visibility, as through the provision of supplementary lighting or the addition of highly coloured features or contrasts.

3 An alternative output that stimulates the non-visual senses, such as with liquid level indicators, tactile scales, vibrating watches and voice recorders.

4 Safety modifi cations that help the visually impaired person avoid conventional non-safe tasks, such as egg slicers.

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Non-optical and sensorial aidsJames S. Wolffsohn

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Although not specifi c to assisting those with visual impairment, a fi fth category of appliance is often available through adaptive aid centres:

5 Appliances with modifi cations designed to assist anyone with a physical infi rmity, such as easy-grasp handles, mounted cup holders and pill organisers.

These aids are generally available from resource centres in the voluntary sector. Others are available free of charge as part of a social care support service or from the service industries (such as cheque-book guides). Those registered as partially sighted or blind can often avoid ‘value added tax’ and avail themselves of free postage in the UK. Funding for adaptive equipment provision is sometimes available from the statutory or voluntary sectors.

Studies into the various types of adaptive equipment issued to people with a disability deal mainly with the use of home adapta-tions, such as bathroom aids and electronic adaptations for people with degenerative neuromuscular conditions.1 They show that suitability and adequate training seem to contribute to more posi-tive rates of use, although few studies have used control groups in their methodologies. Studies also show both perceived2 and actual3 benefi ts resulting from the prescription of such devices for the completion of everyday tasks.

This chapter cannot highlight all the non-optical and sensorial aids available at the present time and the market is constantly advancing. Instead, it aims to describe some of the most widely used and benefi cial aids, which may come in several different forms from a variety of different manufacturers.

15.2 Daily living

There are many simple non-optical and sensorial aids that can assist the visually impaired in their everyday lives.

15.2.1 In the kitchen

Increasing safety is a key issue in the kitchen, as everyday living requires the use of knives, matches, cookers, and hot foods and liquids (Figs 15.1–15.3 [Plates 16–18]). Key items include:

• Liquid level indicators – these devices clip on to the side of a container such as a cup, glass or bowl and have two prongs

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Figure 15.1 (Plate 16) High contrast, large print, tactile cooking items.

Figure 15.2 (Plate 17) Other items for the kitchen.

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pointing into the vesicle. In fi lling the container, when the liquid reaches the level of the prongs it completes an electrical circuit and the liquid level indicator emits a tone and/or vibration. Most allow two different levels to be determined, so that, for example, enough room can be left for milk to be added to tea, and to ensure that when the milk is added the cup does not overfl ow. This aid is particularly useful in the early stages of visual impairment, but those who have adapted well, over time, to impaired or lost sight often use the changing sound of a liquid entering an enclosed container to determine the height of the liquid.

• Easy-to-see timers – the ability to time is an important task in cooking. Although timers usually indicate completion using senses other than sight, such as sound and vibration, they can often be diffi cult to set and it may be diffi cult to monitor how much time is remaining. The visually impaired benefi t from timers that have large, high contrast, print, whereas those without sight benefi t from timers with a tactile rotating dial.

• Food slicers – to avoid the use of a knife, foods such as boiled eggs, apples and tomatoes can be sliced using a wire mesh grid.

Figure 15.3 (Plate 18) Marked up cooker, cup with liquid level indicator, and high contrast kettle.

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• Chopping boards and knives – high contrast (usually white and non-patterned, as foods are often dark in colour), non-slip (textured) boards can make chopping safer. When used in conjunction with knives with adjustable guides, the process becomes safer still.

• Tray liners and holders – these can assist in increasing contrast and reducing slippage.

• Plate surrounds – these prevent food falling off the plate and can provide a visual marker when using patterned or darker plates, where contrast with respect to the food is poor.

• Talking microwaves and scales – these use the sense of hearing to assist those with limited or no sight when preparing and cooking food.

15.2.2 Around the house

The home environment can be learnt in terms of layout and the control of features, but many aids are available that assist in per-forming more taxing visual tasks: Key items include:

• Audible thermometers – to allow the ambient room temperature to be determined.

• Speaking signs and digital voice recorders – can record and play back messages that can welcome a visitor, avoid the need for leaving a written note or warn of nearby obstacles.

• Rain alerts – a sensor plate that emits a sound or vibrates when it gets wet. These are particularly useful when using outdoor clothes-drying facilities.

• Needle threaders – can be simple devices with a loop of metal to put though the eye of the needle. The thread is then placed through the large metal loop, which is drawn back out of the eye of the needle, thus threading it. More complex devices are also available that involve placing the needle, eye end down, into a small tube and the thread into an adjacent slot, before sliding a button across to thread the needle.

• Button guides – brightly coloured and variably shaped buttons that can be used to indicate an item of clothing and assist with colour coordination.

• Tape recorders – the incorporation of high contrast, large print controls allows talking book tapes to be inserted and listened to more easily.

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• Big button telephones – large button telephones, with large high contrast characters. These often include features such as an easy-grip handset, volume control and inductive coupler (to assist those who are hard of hearing), a button to identify the last caller, last number redial and pre-programmed numbers to reduce the visual input needed.

• Watches and clocks – large print, high contrast, tactile (often with an opening transparent front), vibrating and talking varieties are available in many different styles (Fig. 15.4).

• Games – large print, high contrast and tactile playing cards, bingo cards and various board games are available (Fig. 15.5 [Plate 19]).

Figure 15.4 High contrast and talking clocks and watches.

Practical advice

Although optical aids can often give suffi cient magnifi cation to allow someone with visual impairment to read the printed material they desire, the appliance may not provide suffi cient acuity and contrast reserves, with the result that the task can remain diffi cult. In these circumstances, the use of other senses, such as listening to talking books rather than reading, can aid ‘reading’ for pleasure and relaxation.

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• Garden cane tops – brightly coloured and fl exible caps, which can increase safety and reduce the risk of eye injury, particularly in the garden.

15.2.3 Medical and personal care

Maintaining medical and personal care is essential, particularly with the increased prevalence of disease in the elderly. Adaptive aids include:

• Large syringes – these can have both tactile marks and large, high contrast print at key settings. Many insulin-dependent diabetics now prefer insulin pens, which avoid the need for large needles; dose rates can also be preset.

Figure 15.5 (Plate 19) Large print, high contrast and tactile games.

Practical advice

It is important to consider the visually impaired person as a whole, not just as a pair of eyes, because needs such as injecting insulin, which can be visually demanding, are essential to maintaining general health.

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• Pill organisers – these come in various shapes and sizes, and allow pills to be arranged by the day of the week and/or period of the day. They make the process of handling pills easier and help the visually impaired person to remember whether pills have been taken. Loading can be organised in advance by a fully sighted friend or relative, thus avoiding the stress of having to interpret information on medicine bottles and differentiate between similar looking tablets (Fig. 15.6).

• Eye-drop dispensers – designed to assist in the self-administration of eye-drops, these have a guide to assist aim and side pads to assist in squeezing the bottle.

15.2.4 Writing

Writing is a key form of communication, and is usually made more diffi cult by visual impairment. Although optical magnifi cation can assist in checking what has been written, such low vision aids

Figure 15.6 Medication organisers.

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(LVAs), especially if high powered, have a limited space between their lens and the writing surface, and make the writing task more laborious.

The use of non-optical aids can assist in keeping the lines of writing straight (writing frame, thick or raised lined paper; Fig. 15.7 [Plate 20]) and in increasing the visibility of the print by enhancing the contrast (using a black pen on white paper) and size (using felt/fi bretip or gel pens, which place signifi cantly more ink on the page than traditional biros; Fig. 15.8 [Plate 21]). An addi-tional benefi t of the felt-tip or fi bre-tipped pen is that it can be held at a markedly reduced inclination angle to the page and still deliver ink. This is not the case with traditional biros, which are of little use when used in conjunction with a stand magnifi er. The use of a computer, especially if touch typing has previously been learned, can allow writing to continue with greater levels of visual impairment, particularly with the use of screen enlargement and enhanced screen contrast.

Figure 15.7 (Plate 20) Writing guide, typoscope, and raised and thick lined paper.

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15.2.5 Reading

Reading is usually enhanced by magnifi cation (see Ch. 9), but the level of magnifi cation needed can be reduced by the use of contrast and appropriate lighting (see Section 15.5 below). Typo-scopes (usually black card or plastic sheets with a section or sections removed) can be placed as an overlay and thus reduce the glare from the page and assist with the task of keeping to a straight line or fi nding the appropriate section on a cheque, for example.

Figure 15.8 (Plate 21) Range of writing implements and the visibility of their ink against a white paper background.

Practical advice

The use of a black felt-tip or gel pen can often enhance the ability of a person with visual impairment to write ‘more normally’ without the need for optical magnifi cation aids. Touch typing is a really useful skill for someone who becomes visually impaired.

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15.2.6 Travelling and mobility

The environment outside the home is usually less familiar, and non-optical and sensorial aids can assist in moving around, allow-ing independent living and remaining safe. Such items include:

• Refl ective bands – to make a visually impaired person more visible, particularly at night and in poor visibility.

• Tinted glasses – although there has been much research in this area, the subjective benefi ts of tinted lenses4–6 have been diffi cult to quantify in terms of visual function measures. Grey lenses can help to reduce glare and ultraviolet light, without affecting colour vision.7 Blue-blocking (yellow/orange) lenses produce contrast benefi ts when bright targets are seen against short wavelength backgrounds, such as the sky,7–10 and reduce glare.11 A trial in an appropriate environment should always be advised before purchase.

• Sunvisors, umbrellas, hats and caps – all assist in reducing glare, particularly from the sun.

• Coin holders and wallets – can be used to help organise coins and notes, and thus reduce potential embarrassment and confusion when out shopping.

• Canes – these come in different types (Fig. 15.9 [Plate 22]):• Symbol cane – these are designed simply to indicate visual

impairment and do not have the strength to be used as a mobility cane or to provide support. Telescopic, extending and modular versions are available; they are usually white and can have refl ective strips attached.

• Long cane – these should never be provided without specialist training (see Section 16.5.2). People with little or no vision, or extensive visual fi eld loss, generally use them to navigate while walking. The length of the cane is determined principally by the person’s height and walking stride.

Practical advice

Canes should be supplied only in conjunction with appropriate training to ensure the safety of both the visually impaired person and others in their immediate environment. Training should be provided only by qualifi ed personnel.

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• Guide dogs – these are an expensive yet highly versatile mobility aid and companion for those with fairly profound visual loss. The majority of users, of whom there are approximately 5000 in the UK, are young, fi t and healthy, and have longstanding visual impairment.12

• Electronic aids – a variety of electronic mobility aids have been marketed, such as:• Sonic aids – use projected sound waves to determine

the presence and distance of nearby objects (similar to radar).

• General positioning satellites (GPS) – similar to those used in car navigation, which can inform a user of their location to a matter of metres and assist with location-specifi c warnings and information.

• Blue-tooth technology – short-range wireless communication (with a maximum range of 10 metres used in computing and mobile telephone technology) will in the future allow the visually impaired to seek information

Figure 15.9 (Plate 22) Mobility and symbol canes.

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from visually demanding objects of interest in the environment, such as bus times and street names.13

15.3 Labelling

Although much of the instrumentation used in daily life has a variety of settings, it is unusual for people to use more than a few different combinations. The visually impaired can be greatly assisted if the settings that they are most likely to use can be highlighted by increasing their size, tactile nature and contrast, thus providing additional information. For example:

• Self-adhesive, high visibility ‘bumps’ can be placed on a telephone or computer keyboard as position markers.

• Dymo tape can be imprinted with large print or Braille and stuck to storage containers.

• High visibility, thick ‘paint’ can be used to indicate key settings on washing machines and cooker dials.

15.4 Electronic aids

Electronic vision enhancement systems (EVES) provide magnifi ca-tion through non-optical means and are considered in detail in Chapter 14. Computers and stand-alone instrumentation and

Practical advice

In the society in which we live, it is not always benefi cial for individuals to highlight the presence of disability. Practitioners should be conscious of the fact that visually impaired persons may feel vulnerable when using mobility aids that draw attention to the fact that they have impaired sight.

Practical advice

Have some labelling aids available in your low vision kit to demonstrate to patients, even if you do not visit their home environment to make adaptations yourself. These tactile aids can also be used to enhance switches or the battery compartments of magnifi cation aids.

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equipment can be used to print and convert text to tactile lan-guages such as Braille and Moon. In combination with scanning and letter recognition software, they can output speech and provide relative size enlargement (Fig. 15.10 [Plate 23]). There are also several programs available to confi gure the size and contrast of print on a computer screen and to enhance screen navigation. Conventional software often has support settings that give the user the option to customise the presentation style. It is important to ensure that the package recommended or chosen is compatible with the programs that are currently used by the visually impaired person.

Figure 15.10 (Plate 23) Electronic reader.

Practical advice

As electronic vision enhancement systems and specialist software are relatively expensive, it is of great benefi t if a patient can try the system and get some training at a resource centre for the visually impaired before purchasing.

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15.5 Lighting and contrast

Lighting has been shown to have a signifi cant effect on both mobil-ity14 and reading.15 Most people with low vision read in their living room or at the kitchen table, where lighting is often inadequate, with few understanding the need for good lighting (Fig. 15.11).16 The intensity of light falling on an object is proportional to the intensity of the source and the reciprocal of the distance squared (inverse square law). Therefore, to quadruple the light intensity falling on a book that is being read, the intensity rating of the light could be quadrupled (e.g. a 30-W bulb could be replaced by a 120-W bulb, costing more to illuminate and causing more heat – reducing safety) or the distance between the light source and the book can be halved (e.g. from 1 m to 50 cm).

Figure 15.11 Lights, large print phone and writing guides/typoscopes.

Practical advice

Focal lighting can enhance performance in tasks such as sewing and reading music, which are diffi cult to achieve through the provision of optical magnifi cation LVAs.

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Lighting is also an important feature of optical LVAs. The power supply can be provided by batteries (usually located in the handle) or mains supply. Traditional tungsten bulbs are being replaced by light emitting diodes (LEDs), which draw less current (so the bat-teries last longer) and are more robust (so the bulbs last longer). Lighting is more important in stand magnifi ers than hand magni-fi ers, as the stand usually prevents most outside illumination falling on the object of interest. As a consequence, stand magni-fi ers are usually white in colour to ensure that the majority of the light that is inside the magnifi er is refl ected on to the object of regard rather than being absorbed.

Most objects in the real world are not of high contrast, and therefore the measurement of high contrast visual acuity alone is insuffi cient to characterise visual function. Contrast sensitivity has been shown to be a good predictor of reading rate and mobil-ity,14,17 and increasing task contrast is therefore an important non-optical adaptation for those with visual impairment. Contrast can be optimised by using plain (non-patterned) backgrounds (such as on plates) with a contrasting foreground (such as black writing on a white page, or a black handrail against a light wall). Lightly coloured fl oors can assist in observing obstructions (usually of a darker colour), and a band of dark colour around the fl oor edges can assist mobility when both walls and fl oors are pale.

15.6 Summary

• Patients interact with the world using more than one sense, and if one becomes damaged they are often more reliant on another.

• Many non-optical aids are available; some can avoid the added complication of using enlargement to perform a task.

• Appropriate lighting and contrast can reduce or eliminate the need for enlargement.


• Make sure your patients have access to a centre where non-optical aids can be viewed. Some organisations for the visually impaired sell non-optical aids by mail order; this is important for less mobile patients.

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• If contrast sensitivity seems reduced, lighting and contrast advice and assistance are essential.

• Home environments often have poorer lighting than the consulting room. Make sure patients have focal, preferably anglepoise, lighting for all critical tasks.

• Many public and private organisations have free non-optical aids such as cheque guides for the visually impaired. Encourage your patients to ask, and build up your own database of the services available.

References

1. Hastings Kraskowsky L, Finlayson M. Factors affecting older adults’ use of adaptive equipment: review of the literature. American Journal of Occupational Therapy 2001; 55:303–310.

2. Jutai J, Rigby P, Ryan S, Shone Stickel M. Psychosocial impact of electronic aids to daily living. Assistive Technology 2000; 12:123–131.

3. Hart D, Bowling A, Ellis M, Silman A. Locomotor disability in very elderly people: value of a programme for screening and provision of aids for daily living. British Medical Journal 1990; 301:216–220.

4. Hoeft WW, Hughes MK. A comparative study of low vision patients: their ocular disease and preference for one specifi c series of light transmission fi lters. American Journal of Optometry and Physiological Optics 1981; 58:841–845.

5. Maino JH, McMahon TT. NoIRs and low vision. Journal of the American Optometric Association 1986; 57:532–535.

6. Provines WF, Harville B, Block M. Effects of yellow optical fi lters on contrast sensitivity function of albino patients. Journal of the American Optometric Association 1997; 68:353–359.

7. Wolffsohn JS, Dinardo C, Vingrys AJ. Benefi t of coloured lenses for age-related macular degeneration. Ophthalmic and Physiological Optics 2002; 22:300–311.

8. Luria SM. Vision with chromatic fi lters. American Journal of Optometry and Archives of the American Academy of Optometry 1972; 49:818–829.

9. Rabin J, Wiley R. Differences in apparent contrast in yellow and white light. Ophthalmic and Physiological Optics 1996; 16:68–72.

10. Wolffsohn JS, Cochrane AL, Khoo H, Yoshimitsu Y, Wu S. Contrast is enhanced by yellow lenses due to selective reduction of short-wavelength light. Optometry and Vision Science 2000; 77:73–81.

11. Leat SJ, North RV, Bryson H. Do long wavelength pass fi lters improve low vision performance? Ophthalmic and Physiological Optics 1990; 10:219–224.

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12. Refson K, Jackson AJ, Dusoir AE, Archer DB. Residual visual functions of guide dog owners in the UK. Ophthalmic and Physiological Optics 2001; 21:277–285.

13. Wolffsohn JS, Peterson RC. Current knowledge on electronic vision enhancement systems (EVES) for the visually impaired. Ophthalmic and Physiological Optics 2003; 23:35–42.

14. Kuyk T, Elliott JL. Visual factors and mobility in persons with age-related macular degeneration. Journal of Rehabilitation Research and Development 1999; 36:303–312.

15. Rabin J. Luminance effects on visual acuity and small letter contrast sensitivity. Optometry and Vision Science 1994; 71:685–688.

16. Lindner H, Rinnert T, Behrens-Baumann W. Illumination conditions of visually impaired people under private domestic circumstances – clinical study on 91 patients. Klinische Monatsblatter fur Augenheilkunde 2001; 218:774–781.

17. Leat SJ, Woo GC. The validity of current clinical tests of contrast sensitivity and their ability to predict reading speed in low vision. Eye 1997; 11:893–899.

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CHAPTER

16.1 Introduction

Everybody with a disability learns, to a greater or lesser degree, to rehabilitate themselves. They devise strategies to cope with the diffi culties their disability imposes. Left to their own devices each person will, in time, go as far as their knowledge, imagination and personality will allow. Individuals do, however, often impose arbi-trary limitations on themselves. Some see themselves as being more handicapped than their disability dictates. They may be more aware of what they can no longer do as opposed to what they can still do, more aware of what they have lost than of what they have retained. In this respect the visually impaired are no differ-ent from anyone else. They use expressions such as ‘I can’t see anything any more’ or ‘I only see shadows’, and proceed to re-organise their lives according to how they think ‘blind’ people ought to behave.1

SECTION FOUR

Low vision rehabilitationSection Editor: Owen F. Adams

Rehabilitation servicesOwen F. Adams

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The aim of those involved in the provision of a comprehensive rehabilitation programme is to provide the necessary information and support that will enable visually impaired people to have a more realistic understanding of their vision, the visual processes, the limitations imposed by visual impairment and, most impor-tantly, the elements of vision that have been retained.

The rehabilitation programme should also be designed to dem-onstrate the characteristics of functional vision and to give the individual involved a clear understanding of the tasks that they should reasonably expect to be able to continue to perform. The programme must also identify and address the tasks that could be considered unreasonable, uncomfortable or even dangerous to attempt. It should give the visually impaired person the confi -dence to be able to recognise the visual images upon which they can safely rely and around which they can make good decisions. Ideally, it should enable patients to take decisions that affect their lives and to be active, rather than passive, participants in the reha-bilitation process.

Rehabilitation, within the context of this section, considers the needs of people with some residual vision rather than those of people who are totally blind.

16.2 Rehabilitation delivery systems

Although the legislation covering social services to blind and partially sighted people in England and Wales, Scotland and Northern Ireland is broadly similar, services and methods of service delivery can, and do, vary considerably from one local authority to another. The Chronically Sick and Disabled Persons Acts2–4 contain specifi c duties relating to people who are chroni-cally sick or have a disability. Sections 1 and 2 set out the require-ments placed on local authorities to make such arrangements as are necessary for the provision of social welfare services. Section 1 defi nes the people who are covered by the Act, including those who are deemed to be blind (within the meaning of the National Assistance Act 1948). Section 2 outlines the range of services to be provided, including practical assistance in the home; the enabling of participation in independent travel, recreational activities, edu-cation and employment; and the provision of aids and adaptations. A rehabilitation service should be designed to meet these responsibilities.

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The rehabilitation services described in this section are a syn-opsis of current ‘best practice’ and should not be considered to be a description of what is available in any particular area. A well balanced rehabilitation programme must be built on a foundation of good interdisciplinary contacts maintained between the pro-gramme coordinators, other social services staff, the providers of regional ophthalmic and low vision services as well as those responsible for educational and disabled employment services.5

Rehabilitation services for the visually impaired are provided by specially trained rehabilitation workers employed by social service departments or, under contract, by a voluntary organisa-tion such as the local society for the blind. Their role is quite dis-tinct from that of the social worker, who is also an essential element of the multidisciplinary team. It is the role of the rehabilitation worker to assess rehabilitation needs and to design the rehabilita-tion programme.

Practical advice

Rehabilitation is, in its very nature, holistic. The process can be optimised only within an interdisciplinary environment (either real or virtual), in which professionals work together sharing information and coordinating input at the most appropriate times. The patient is central to the process.

16.3 The rehabilitation programme

The programme should be designed to provide the recipient with the necessary knowledge, skills and techniques to meet the new demands that are imposed by impaired vision. The content of any programme must be mixed and varied, and must ultimately be tailored to individual need.6,7

Sometimes it is more appropriate for the rehabilitation worker to work with the visually impaired person on a one-to-one basis, whereas on other occasions it may be useful to involve the family, for example in demonstrating ‘sighted guide’ skills. Working on some tasks in the home is unavoidable and may even be necessary, but others are best undertaken in a centre to avoid the sort of dis-tractions so often prevalent in the home. Working in a group

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setting can be very benefi cial, particularly for the newly visually impaired person; it allows each member of the group to see that they are not the only person with serious loss of vision, and allows them to interact with others in a similar predicament. Some gain reassurance from realising that others have progressed much further down the road, or may even benefi t from seeing them-selves as being in a position to encourage others who have more recently become visually impaired. Peer support group work, in which newly visually impaired people meet in groups of four to eight to receive professional advice and benefi t from interacting with one another, has been shown to be successful.8 Such groups often maintain friendships beyond the scheduled group sessions, developing peer support group networks in local communities. Some rehabilitation models include visually impaired ‘peer workers’ who can provide reassurance and support.5 Contact with support groups for the visually impaired, particularly those that are disease specifi c, can be benefi cial.6

16.3.1 A model of disability

If we consider the line A–B (Fig. 16.1) to represent the range of a person’s natural abilities, and A–X1 to represent the range of abil-ities they believe they are left with after losing their sight, then X1–B represents the range of abilities they believe they have lost. The extent of X1–B is often greatly exaggerated. This exaggeration arises from fear and lack of understanding rather than from a conscious desire to overstate the situation. It refl ects the emotional aspect of sensory or physical loss, which is now universally regarded as akin to bereavement.9,10

The aim of a properly designed rehabilitation programme is to move point X1 to X2 and thus ultimately reduce the extent of the impact of disability, namely X2–B. The disability itself cannot be removed in its entirety, but its effects can be ameliorated by the

Figure 16.1 A model of disability (see text for explanation).

A

X1

X2

A

A

B

B

B

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use of the other senses, vision substitution and vision enhance-ment (as described below). If referral to a rehabilitation service is made early, this may limit the distance to which X1 drops and, generally, speed up progress to X2, which marks the true extent of the visual disability. Early referral is in the best interest of the patient and this is where other professionals can be of immense help. It is at the heart of the multidisciplinary and interdisciplinary approach to rehabilitation. Referral should not be left to the end of the medical or ophthalmological investigation, but should be made at a time appropriate to needs. The ultimate aim of any rehabilitation programme, and of everyone who makes a contribu-tion to it, must be to maximise the sense of independence of the recipient.

Unfortunately, research has shown that the knowledge of low vision rehabilitation services is generally poor, both in those with visual impairment11,12 and in those treating eye disease.13 Health checks in the elderly rarely consider vision and, even when they do, often assess subjective rather than objective measurement of visual impairment.14,15 In most cases the service is not integrated within secondary care ophthalmological services, and is therefore reliant on external referrals. There is also some confusion over statutory levels of visual impairment (blind and partially sighted), with referral often not seen as being appropriate until these levels are reached.13 Many patients, especially those with age-related macular degeneration (AMD), who make up a large proportion of patients with untreatable visual loss, do not understand the benefi t of low vision rehabilitation services when they have been told by healthcare professionals that ‘nothing more can be done for their vision’ (see Ch. 18).16

Practical advice

When providing, or contributing to, a rehabilitation service the practitioner should ask:

• Which of my skills and services are appropriate for this patient?• At what point in the rehabilitation process is my intervention going

to benefi t the patient most?• Is there another agency to which I should refer this patient?

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16.4 Rehabilitation programme content

As stated in Section 16.2, Section 2 of The Chronically Sick and Disabled Persons Acts places a statutory obligation on local author-ities to assess the needs of disabled people and to provide an appropriate programme of care, which would include a re-habilitation programme. A properly designed rehabilitation pro-gramme is one that is designed specifi cally to meet the needs of the individual. A similar degree of fi eld loss or a loss of central acuity caused by identical pathology will not necessarily create the same sense of disability in different people. For this reason, a well structured process of assessment is essential, and must be multi-disciplinary and interdisciplinary in nature. Every aspect of a person’s life, which they are willing to share, needs to be looked at from both a practical and emotional standpoint.

16.5 The practical problems

In many ways the most obvious problems to be addressed are the practical problems – those dealing with communication (reading and writing), mobility and daily living skills. Indeed, these have been at the core of welfare services for the blind for many years and are still important elements of the modern rehabilitation programme.

16.5.1 Communication

Diffi culties associated with reading and writing are amongst the fi rst things a newly visually impaired person may wish to talk about.5 Methods of dealing with communication issues have changed dramatically over the past 25 years. For example, although learning Braille would, in the past, have been seen as essential for everyone who could no longer read print, today it is taught only to children and adults in education (Fig. 16.2). Recent research indicates that even experienced Braille readers can rarely read Braille at even 50% of the speed achieved by someone reading print.17,18 For those Braille users who wish to improve their reading speed, courses are available that teach techniques for speed-reading; some of these are available free from the internet.19 There is only limited availability of Braille material nowadays and it

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tends to be bulky. For example, it takes many Braille volumes to transcribe an average-size novel.

Modern technology has made the use of Braille largely unneces-sary for most visually impaired people. Better optical and elec-tronic magnifi ers, recording tapes, compact discs and computers with large characters and/or a screen reader and peripherals such as scanners with optical character recognition (OCR) are now available (see Chs 9–15). A screen reader is a software package that enables a speech synthesiser to read aloud the text on a computer screen and enables a visually impaired person to hear what he or she is writing or editing. It also makes the world wide web and the world of e-mail available to the visually impaired. Braille is, however, still seen as essential to the totally blind child in education.

16.5.2 Mobility

Not every visually impaired person needs either a mobility aid or mobility training. This is an area in which individual assessment of need is essential. Rehabilitation workers, who have undergone specialised training, have a wide range of skills and aids at their disposal to enable them to customise a programme for each patient.

Figure 16.2 Reading Braille print.

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There are, for example, a variety of ‘white sticks’ in use (see Fig. 15.9). They range from the white walking stick, for the person who needs support as well as a symbol to let others know the user has a sight problem, to the lightweight symbol cane, which simply lets others know the user is visually impaired. The stronger guide cane and long cane are both used for ‘feeling’ the way. The laser cane is a long cane that emits a pulse of ultrasound or laser light and makes an audible sound, or tactile vibrations under the index fi nger, when the beam detects an obstacle.

The walking stick, symbol and guide canes need minimal instruction in their use, whereas long cane training is intensive. The mobility instructor must be satisfi ed that the trainee is medi-cally fi t to undergo the training programme. After being shown how to hold and ‘sweep’ the cane, the trainee is supervised using it indoors before graduating to a ‘safe’ outdoor environment. When the instructor is satisfi ed with the trainee’s technique, they will move to main roads and city centres as appropriate. At this stage, long cane users will learn specifi c routes, such as from home to, and around, school, college or the workplace (Fig. 16.3). They are made familiar with the layout of other buildings or environments

A C

B

Figure 16.3 A–C, Long cane user and canes. (Courtesy of GDBA.)

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they frequent, such as the Underground, as well as bus and train stations. Training can take several months.

A range of guiding and orientation skills can also be taught for both indoor and outdoor use. In this instance, not only is the visu-ally impaired person trained in the use of the guiding techniques, but so are friends, family members and colleagues.

Guide dogs are used by only approximately 3% of the visually impaired population.20,21 Here again, an intensive course of instruc-tion has to be undertaken. Having been accepted as a potential guide dog user, the visually impaired person has to wait until a dog of the appropriate size, weight and temperament is available before training can commence. Initial training in the care and handling of the dog is carried out at one of the guide dog centres (see Appendix) before road work commences. After that, an instructor will go home with the new user and carry out a famil-iarisation programme on routes and frequently used locations (Fig. 16.4 [Plate 24]). The Guide Dog Associations like their guide dog users to be profi cient in the use of the long cane as a backup for when the dog might be indisposed.

16.5.3 Daily living skills

There are many daily living tasks that create problems for the visually impaired. They range from threading a needle to knowing the temperature of the oven, from addressing an envelope to cutting the lawn. A body of knowledge has been built up over many years and is, in the main, a compendium of techniques that

Figure 16.4 (Plate 24) Guide dog and user. (Courtesy of GDBA.)

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have been developed, often by visually impaired people them-selves, to overcome these problems.22 Many of the techniques utilise sight enhancement, such as templates to assist the writing and signing of cheques, benefi t vouchers and addressing enve-lopes, whereas others involve sight substitution, for instance needle-threaders, tactile measuring tapes and bumpons (small adhesive patches) that can be used to locate specifi c keys on a keyboard or mark settings on cookers and washing machines (see Ch. 15; Figs 16.5 & 16.6).

16.6 Emotional problems and counselling

The term counselling is often used without any regard for its professional meaning. Professional counselling is not about giving people advice, nor is it about telling people how they ought to behave or what their reaction to an event ought to be. It is to help the person come to a well informed decision on a course of action based on an objective examination of their choices. It is the patient who must recognise and examine the choices that are available and come to their own decision about which course of action to follow. To do this effectively, the counsellor must have not only a knowledge of counselling skills, but also a sound knowledge of the problems associated with functional visual loss.23 It should be recognised that there are emotional issues for the professionals involved in low vision rehabilitation as well as for the patients themselves. It is, perhaps, the most emotionally demanding area of optometric/ophthalmic practice, and practitioners must be aware of the associated psychological pressures that they too may

A BFigure 16.5 Washing machine seen with normal vision (A) and how it might be seen by someone with visual impairment (B).

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face.24 This can be very apparent when working with the parents of newly diagnosed and, so often, multiply disabled children (see Ch. 2).

Most of us – and it must be stressed that the visually impaired are no exception – are reticent to express inner feelings resulting from pain and suffering. This is particularly the case when the circumstances are still changing and emotional pain is still acute. Those experiencing loss of vision go through a process similar to the bereavement process and experience all the emotional turmoil associated with it. Rehabilitation, if it is to get to the heart of the matter, must deal not only with the practical issues but with those of the heart and mind.

AB

C

D

Figure 16.6 Techniques to overcome problems of visual impairment. A, Tactile measuring tape; B, automatic needle threader; C, envelope writing guide; D, allowance book signature guide. (Courtesy of the Royal National Institute for the Blind.)

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16.7 Certifi cation, registration and rehabilitation services

The fi rst thing to be said about becoming registered as a visually impaired person is that it is absolutely voluntary. The procedure requires that the patient is examined by a consultant ophthalmolo-gist. If the examination confi rms that the patient meets the criteria required for registration (see Ch. 1), the examining ophthalmolo-gist will complete the appropriate forms, which are then forwarded to the appropriate social services department where, with the consent of the patient, registration will take place. In some parts of Scotland the local blind welfare society has been designated as the appropriate authority, whereas in the Republic of Ireland it is the National Council for the Blind. For benefi t purposes, the date of certifi cation is important as benefi ts may be calculated from that date (for example, when claiming the Blind Person’s Income Tax Allowance). In Britain there is a statutory obligation on social services departments to maintain registers of blind and partially sighted people. In Northern Ireland, legislation requires social service trusts to keep a record of all ‘handicapped’ people who are living in their area using, or likely to use, services. These records include blind and partially sighted people. A Register of Blind Persons is maintained by the National Council for the Blind in the Republic of Ireland, where there is only one category of visual impairment. The clinical information on the certifi cate is, however, essential to the rehabilitation worker in planning a com-prehensive rehabilitation programme, including any low vision therapy.

Practical advice

Think ahead and ask questions that demonstrate empathy:

• Ask about communication. Can the patient read their correspondence and reply accordingly? Enquire as to how much help the patient would like.

• Ask about mobility. Can the patient still go out unaccompanied, function in an unfamiliar environment, cope after dark?

• Ask about daily living tasks. Can the patient use the cooker, make a cup of tea, manage with personal care, write a shopping list?

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Certifi cation and/or registration is not necessary for entry to social or rehabilitation services. The national review of the whole certifi cation and registration process in the UK, which was com-pleted in 2004, has been carried out in such a way as to ensure that visually impaired persons receive more information about ser-vices from the range of professionals they are likely to come into contact with concerning their ocular health and vision.

16.7.1 The new forms and categories of certifi cation

As a result of the above-mentioned 2004 review, the terminology used in respect of visual impairment and the forms used to certify and refer patients to social services have changed.

A Certifi cate of Vision Impairment (CVI) is completed by a consultant ophthalmologist who, with the patient’s consent, certi-fi es that a person is either severely sight impaired (formerly ‘blind’) or sight impaired (formerly ‘partially sighted’). The form is then forwarded to social services for (with the patient’s consent) regis-tration and access to services.

A Referral of Vision Impaired Person (RVI) can be completed by staff in the hospital’s ophthalmic department and, with the patient’s consent, forwarded to social services as a means of access-ing appropriate services. It does not lead to registration, nor does it entitle a person to social security benefi ts.

A Low Vision Leafl et (LVL), replacing the original Letter of Vision Impairment (LVI), may be obtained from an optometrist and is used by the patient as a means of self-referral to access health or social services.

16.8 Allowances, benefi ts and concessions arising from registration

As registration presupposes certifi cation, the term ‘registration’ is used throughout the rest of this section. People who are registered as visually impaired are entitled to certain allowances, benefi ts and concessions. These are dependent upon whether the person qualifi es for registration as blind or partially sighted.

16.8.1 Allowances

A person registered as blind can claim an additional income tax allowance, which may be transferred to the spouse if necessary;

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a Disabled Person’s Tax Credit is available to people in work. Either or both the care and mobility components of the Disability Living Allowance are available to people under the age of 65 years, with Attendance Allowance being available if over 65 years. Other allowances include Disability Working Allowance and Severe Dis-ablement Allowance, and for people providing full-time care there is the Invalid Care Allowance.

16.8.2 Benefi ts

People registered as either blind or partially sighted may qualify for Housing Benefi t as well as Incapacity Benefi t, as possible alter-natives to the Job Seeker’s Allowance or additional income support premiums.

16.8.3 Concessions

Council tax or rates relief can be claimed in respect of structural alterations specifi cally undertaken for reasons arising from dis-ability. Blind people can claim a 50% reduction on the television licence fee, and British Telecom provides a free directory enquiry service. There is free postage on articles specifi cally for the blind. Help may also be available for residential or nursing care costs, and a free National Health Service eye test is available to people who have been registered as blind or partially sighted in England, Wales and Northern Ireland; since 1 April 2006 everyone in Scotland is entitled to a free NHS eye test whether they are visu-ally impaired or not. A postal vote or proxy vote, as well as assisted voting in person, is available at elections.

Blind people and the partially sighted who have mobility prob-lems may apply for the Blue Badge disabled parking scheme. The travel concessions that are available vary according to the mode of transport, and most are dependent on where the blind person resides. For example, in Northern Ireland and in some regions of Britain, a registered blind person may apply for a pass that allows un-accompanied free travel on local buses and trains. In Great Britain, a Disabled Person’s Railcard is available for unaccompanied travel on longer train journeys, at a concessionary fare.

All of the above allowances, benefi ts and concessions are avail-able to all registered blind people who meet the criteria, and many of them may be available to those who have been registered as partially sighted.25

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Probably the most enduring misunderstanding, or myth, is that there is a ‘blind pension’. In the UK that pension, worth 25 shil-lings (£1.25) per week, was abolished with the introduction of the National Assistance Act in 1948. However, a means tested and age-related benefi t of that name, worth up to 8500 euros per annum, is available in the Republic of Ireland.

16.9 Summary

Referral for low vision rehabilitation can be initiated by anyone, but should be made only with the patient’s consent. The ultimate aim of rehabilitation is to increase understanding about residual visual functions and to maximise the sense of independence of the recipient. A properly designed multidisciplinary rehabilitation programme must address the practical problems of communica-tion (reading and writing), mobility and daily living skills. The emotional aspects of sensory loss must also be addressed.

The decision to be registered as a blind or partially sighted person is absolutely voluntary. People who are registered may be entitled to certain concessions and social security benefi ts. Discus-sion concerning benefi ts and concessions should be left to those with expertise in the area.

References

1. Genensky SM. Acuity measures: do they really indicate how well a partially sighted person could function. American Journal of Optometry and Phsyiological Optics 1976; 53:809–812.

Practical advice

Social services staff, voluntary organisations working with the visually impaired, and Citizens Advice Bureaux maintain up-to-date information on the benefi ts, allowances and concessions associated with registration.

Explanations concerning benefi ts, allowances and concessions that may result from registration are best left to those with specifi c experience in the fi eld, as they are fraught with nuances that often lead to misunderstandings and disappointment.

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2. Chronically Sick and Disabled Persons Act (England & Wales) 1970 and Amendment Act 1976. London: HMSO.

3. Chronically Sick and Disabled Persons Act (Scotland) 1972. London: HMSO.

4. Chronically Sick and Disabled Persons Act (Northern Ireland) 1978. London: HMSO.

5. Wolffsohn JS, Cochrane AL. The changing face of the visually impaired. The Kooyong Low Vision Clinic’s past, present and future. Optometry and Vision Science 1999; 76:747–754.

6. Dodds AG. Motifi cation reconsidered: the importance of self-effi cacy in rehabilitation. British Journal of Visual Impairment 1989; VII:11–15.

7. Adams OF. How the blind see. The New Beacon 1985; 813:1–3. 8. Van Zandt PL, Van Zandt SL, Wang A. The role of support groups

in adjusting to visual impairment in old age. Journal of Visual Impairment and Blindness 1994; 88:244–252.

9. Parkes CM. Bereavement: studies in grief in adult life. London: Penguin Books; 1998.

10. Warden JW. Grief counselling and grief therapy. London: Routledge; 1991.

11. Long CA, Holden R, Mulkerrin E, Sykes D. Opportunistic screening of visual acuity of elderly patients attending out-patient clinics. Age and Ageing 1991; 20:392–395.

12. Gresset J, Baumgarten M. Prevalence of visual impairment and utilization of rehabilitation services in the visually impaired elderly population of Quebec. Optometry and Vision Science 2002; 79:416–423.

13. Keefe JE, Lovie-Kitchin JE, Taylor HR. Referral to low-vision services by ophthalmologists. Australian and New Zealand Journal of Ophthalmology 1996; 24:207–214.

14. Malhotra R, Pate J, Smeeth L, Malhotra R. Are elderly people being screened for visual impairment in general practice? Eye 2001; 15:98–99.

15. Evans BJW, Rowlands G. Correctable visual impairment in older people: a major unmet need. Ophthalmic and Physiological Optics 2004; 24:161–180.

16. Mitchell J, Bradley P, Anderson SJ, Ffytche T, Bradley C. Perceived quality of health care in macular disease: a survey of members of the Macular Disease Society. British Journal of Ophthalmology 2002; 86:777–781.

17. Legge GE, Madison C, Mansfi eld JS. Measuring Braille reading speed with the MNREAD test. Visual Impairment Research 1999; 1:131–145.

18. Bailey J. Surmounting the Braille reading speed plateau. The Braille Monitor 2003; 46(5):323–325.

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19. Percy Hedley Foundation. Online. Available: http://www.percyhedley.org.uk/

20. Jackson AJ, Murphy PJ, Dusoir T, Dusoir H, Murdock A, Morrison E. Ophthalmic, health and social profi le of guide dog owners in Northern Ireland. Ophthalmic and Physiological Optics 1994; 14:371–377.

21. Refson K, Jackson AJ, Dusoir AE, Archer DB. Ophthalmic and visual profi le of guide dog owners in Scotland. British Journal of Ophthalmology 1999; 83:470–477.

22. Ford M, Heshel T. The In Touch handbook. Cardiff: In Touch Publishing; 1995.

23. Dryden W, Charles-Edwards D, Woolfe R. The handbook of counselling in Britain. London: Routledge; 1989.

24. Crossland MD, Culham LE. Psychological aspects of visual impairment. Optometry in Practice 2000; 1:21–26.

25. National Council for the Blind of Ireland. Benefi ts and allowances for blind and visually impaired people. Information Service Fact Sheet. Dublin: National Council for the Blind of Ireland; 2003.

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17.1 Introduction

When a person sustains a permanent loss of vision they can be said to have acquired ‘new’ or ‘different’ visual equipment. When they attempt to use the ‘new’ equipment in the way they were accustomed to using its predecessor, they fi nd that it no longer meets their needs. In any other fi eld of activity, when we acquire a new, or different, piece of equipment we need to read the ‘book of instructions’ to enable us to make the best use of it. Low vision therapy helps patients to use their eyes in such a way that they derive maximum benefi t from their residual vision. It is teaching them consciously to develop new visual habits. The role of the low vision therapist in the context of rehabilitation is, as it were, to write a book of instructions or a user’s guide customised for each patient with low vision. There is no universal solution that will work for every individual.

17.2 A user’s guide to low vision

As is the case with any instruction manual, a user’s guide must describe how the item works and the methods of use that will optimise performance. The low vision user’s guide must, there-fore, address the following issues.

308

CHAPTER

Low vision therapyOwen F. Adams

171717

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17Low vision therapy 1717

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17.2.1 How vision works

This would involve a simple explanation, in lay terms, of the anatomy and physiology of the human eye and visual system. It must specifi cally include an explanation as to the signifi cance of the refractive components within the eye and how refractive errors are corrected. One of the questions most often asked is: ‘Why can’t they just give me a stronger pair of glasses?’ This needs to be answered and the reason explained. Another question asked is: ‘Would contact lenses be of any help?’ A basic understanding of the respective optics of contact lenses and spectacles is required to address this question. Good interdisciplinary liaison can help to negate the impression, often held by the patient, that the advice of a previous practitioner is at odds with that currently being delivered. A basic understanding of surgical techniques, such as cataract extraction and photodynamic therapy, is also necessary to assist the patient and their supporters.

17.2.2 Why the patient’s vision is different

Again, a simple explanation is required, in lay terms, of the par-ticular disease process that has led to the loss of vision. Explana-tions must also be given as to why, if this is the case, the refractive processes remain unaffected by the impairment. It is often helpful to reiterate explanations to accompanying family or friends.

17.2.3 How the patient’s vision is different

This means providing the patient with an appreciation of the ele-ments of vision that have changed or been lost. This may involve describing how damage to the visual system in age-related macular degeneration (AMD), for example, results in a loss of central acuity. It may also involve illustrating how the central visual system can be damaged in such a way as to make low contrast tasks much more diffi cult to perform than high contrast tasks. A description of how conditions causing peripheral fi eld loss can infl uence how vision is used may also be required.

17.2.4 How to use residual vision

This would include an explanation and demonstration of good visual habits. Ultimately, this should encourage the patient to

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maximise residual vision to best effect. For example, patients may need to be taught techniques for the use of eccentric vision within both near and distance contexts (see Section 17.4).

17.2.5 How to enhance residual vision

Patients must be made aware of the growing range of low vision aids (LVAs) in the armoury of the optometric/ophthalmic rehabili-tative service. Their use of any optical aids that have been pre-scribed should be monitored and, when necessary, additional training offered in the appropriate use. Patients must also be encour-aged to maximise visual performance through the use of optimal lighting and contrast enhancement (Chapter 15). Advice on glare avoidance may be required, and the benefi ts of variable working distances should be demonstrated. For patients who have corrective lenses, advice on their continued and appropriate use may be required.

17.2.6 How to substitute for lack of vision

Patients should be encouraged to look to their other senses. We all use our senses of touch, hearing, taste and smell to a much greater extent than is generally recognised. The visually impaired need to be made consciously aware of the value of developing the use of these other senses. Visually impaired people do not miracu-lously, at the onset of impairment, become supra-sensory beings.

Using touch for Braille, tactile clocks and watches is one of the most obvious examples (Fig. 17.1). Touch is also useful in identify-ing money, locating lost objects and distinguishing garments by the feel of the fabric.

Hearing can be a useful substitute for, or used in combina-tion with, sight when, for example, using domestic appliances (talking microwave ovens and central heating timers), telling the time (talking clocks and watches), fi lling a glass or cup (liquid level indicator or listening to the pitch increase) or reading (talking newspapers and audio books) (see Ch. 15). Likewise, computers with synthesised speech can prove invaluable to those in education and employment. Identifying people by their voice and listening for traffi c beyond the visual horizon are other examples.1

Taste can be used to identify similar looking substances, such as salt and sugar. The visually impaired may have reason to use

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this sense more often; they should, however, use it with great caution.

The sense of smell can also be used very effectively. Foodstuffs that may look and feel similar to the visually impaired may be differentiated by smell. Many shops have a distinctive smell – pharmacies, shoe shops and, of course, fi shmongers. These cues can be an invaluable help to the visually impaired.

17.2.7 How to live with impaired vision

Any loss has its emotional implications (see Ch. 5). Loss of vision is potentially no less devastating than any other serious loss. Frus-tration and depression are as much a part of visual impairment as are reduced acuity or restricted fi elds. It is common for newly visually impaired people to try to minimise their diffi culties and hide their feelings, but practitioners must recognise that only the most insensitive person would not feel some degree of depression at the loss of such a vital function as vision.

A

B

C

Figure 17.1 A, Talking clock. B, Tactile watches. C, Liquid level indicator. (Courtesy of the Royal National Institute for the Blind.)

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A person depressed at the loss of vision does not usually appre-ciate the value of residual vision and will not readily respond to being encouraged to use it. Although the degree of depression may vary, or appear to vary, from one person to another, these issues need to be understood and addressed within the context of re-habilitation, particularly on those occasions when loss of vision is the topic under discussion.2

17.3 Low vision therapy

Having given a patient the necessary information to enable them to have a more realistic understanding of their vision, the vision processes, the limitations imposed by the visual impairment and, most importantly, the elements of their vision that have been retained, the next step is to show, and encourage, them to use their residual vision to its best advantage.

As the physiotherapist works with physical dysfunction, the low vision therapist works with a sensory dysfunction (visual impair-ment). Just as the cause of the visual impairment – the pathology or disease process – dictates the dysfunction (impairment), so the dysfunction and the personality of the patient dictate the specifi cs of the vision training that is required.3

Many visually impaired people unconsciously develop visual habits such as staring, reduced blink rates, head tilt and visual ‘switch off’. The object of low vision therapy is to redevelop healthy visual habits that will enable the patient to maximise use of their remaining vision and so assist them in remaining as independent as possible. This includes being relaxed, adopting a good posture, using a level of illumination appropriate to the task, taking advan-tage of the benefi ts of appropriate contrast and colour, as well as learning to control eye movements consciously.

Practical advice

• Would the patient benefi t from a better understanding of their vision loss?

• Have you the time and experience to provide the advice and help required? If not, who does?

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17.3.1 Posture and relaxation

Sitting comfortably is a necessary prerequisite to being ‘at ease’. Using relaxation techniques to relieve tension and anxiety leads to a better response from the patient. A patient who is relaxed generally responds better and so performs optimally. Bad posture mitigates against good performance. This is particularly relevant when using hand or stand magnifi ers at a table or desk. Being hunched over a desk or table may constrict the airways, particu-larly in the elderly. Good breathing is an important element in optimal performance.

17.3.2 Lighting

Lighting needs to be customised for each individual, and for every task. There is no one level of illumination to suit everybody in all circumstances. The general injunction, so often given, to ‘use better lighting’ is usually interpreted as meaning brighter lighting. This sort of advice can be ill conceived (see Ch. 15). Tolerance of light varies considerably from one person to another, and may be infl uenced by the presence of medial opacities. A high level of illumination may be tolerable, even benefi cial, to someone with macular degeneration, but quite intolerable to a person with cata-ract or aniridia. On the other hand, a very low level of illumination can make life diffi cult for a person who experiences night blind-ness but assist those with cone dystrophy. As explained in Chapter 15, focal lighting is the key to safe, economical and effi cient illumination.

It will be necessary to demonstrate the effect of different sources of light (tungsten, fl uorescent, halogen), of varying intensities (wattage), at different distances and from different directions, and so select what is, as well as what is not, appropriate for each person in specifi c circumstances.

The advantages of fl uorescent lighting as opposed to the tung-sten fi lament lamp should be borne in mind, the three main advantages being: (1) it is more economical, (2) it operates at a much lower temperature and (3) it is less likely to cast shadows.

The intensity of the illumination on a task, whether it be reading, sewing or wiring an electric plug, can be varied by changing the distance of the source of illumination, so it is useful to explain the inverse square law (see Ch. 15, Section 15.5).

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Issues around lighting in the homes should also be addressed. Light is often inadequate for safe mobility, such as in hallways and on stairs, and for detailed tasks in the kitchen or living room.4 Many elderly people, who constitute the vast majority of the visu-ally impaired, tend to use low wattage tungsten lamps. The choice is often dictated by perceived cost rather than comfort. A 20-watt fl uorescent lamp burning non-stop for two whole days would use less than 1 unit of electricity, whereas a 150-watt tungsten lamp would use 1 unit in less than 7 hours. It is, therefore, economical to leave these low energy lamps burning all evening in hallways and on landings to illuminate staircases. This contributes to safety in the home as well as good economics.

17.3.3 Contrast and colour

Visual impairment can result in diffi culty in distinguishing between a wide range of colours. There may be no diffi culty in recognising the difference between light grey and dark grey, or between beige and dark tan. The problem often arises from diffi -culties with contrast rather than with colour per se. People with central loss from, say, macular degeneration are often thought to be colour blind, although if you ask them to look at a piece of thread or wool through a LVA under appropriate lighting they can quite readily tell you the colour.

Demonstrating the presence of colour vision and its use in prac-tical circumstances can be invaluable to the visually impaired. Every practitioner should, within their consulting room, keep examples of coloured materials to demonstrate the importance of colour contrast. Colour matching can be assisted by the use of different shaded or shaped buttons (see Ch. 15). One should not forget, however, that 1 in 12 males has a congenital colour vision defect that is quite unrelated to their acquired visual impair-ment.5 As such, it is important not to assume that, by increasing object size and brightness, normal colour identifi cation can be achieved.

As with lighting, advice on contrast in the home should be a feature of every rehabilitation programme for patients with low vision (see Ch. 15). Contrast between foodstuffs and the receptacle in, or on, which they are served should be considered, for instance the use of light coloured cups for dark liquids, and dark cups for lighter liquids such as milk. Patterned plates can be confusing, with a fl ower being mistaken for a piece of meat or vegetable. Use

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of a high contrast, non-slip mat or rug at the bottom of stairs to indicate a new level is benefi cial, as is marking the edge of stairs and steps with a contrasting strip. Defi ning doorways by using contrasting colours on the architrave (door frame) and the door should be considered; it is important to remember that patients who experience diffi culties in low levels of illumination can confuse a darkly painted door with an open door. All-glass doors do need to have some feature to indicate their presence. Catering for contrast in decorating means trying to balance the demands of safety with those of aesthetics.

17.3.4 Blinking

Many visually impaired people strain to see and try to fi xate with an unblinking stare. Some actually become self-conscious about blinking. They believe that other people will think it odd. The visually impaired can quite quickly forget or, indeed, may never have noticed what ‘normal’ sighted behaviour was. Reducing the blink rate does nothing to enhance vision and may in fact reduce the quality of the image further as the tear fi lm evaporates and the ocular surface dries. Those with congenital visual loss will be unaware of normal visual behaviour, so guidance on how to adopt normal viewing strategies needs to be given sensitively.

17.3.5 Eye movements

The main purpose of promoting healthy eye movement is to give the patient the means to use their residual vision effectively. It helps them to locate objects in their visual fi eld. Exercises designed to encourage tracking, tracing and saccadic movement can contrib-ute to this.6 Patients should be given simple exercises that they can practise at home. Remind them to blink consciously while they are practising the exercises.

Practical advice

• Keep a selection of light sources available to demonstrate their characteristics and use.

• Keep examples of coloured materials to demonstrate the importance of colour contrast.

• Explain the role of lighting and colour contrast in safety.

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Tracking exercises should be designed to encourage the patient to follow a moving object by moving the eyes while utilising minimal head movement. A simple example of this type of exer-cise is as follows: while standing at a bus stop to look straight across the road, the patient should turn the eyes as far as is com-fortable to, say, the left, pick up a vehicle coming towards them and track it until it is out of sight. This can then be repeated in the opposite direction.

Tracing involves moving the point of fi xation along a fi xed line. Select a large rectangular area such as a large window, door or one wall of a room. Start the patient fi xating on a point at the centre of the object then, without moving the head, move the eye to one corner and start tracing slowly along to an adjacent corner, then to the next and so on back to the fi rst corner. When they are comfortable doing this with large areas, ask them to choose smaller areas such as a picture, mirror or television screen. When they have mastered these smaller rectangles, they can start on curved edges such as oval or circular mirrors. Small curved lines are more exacting than straight lines. These tracing exercises should be carried out in both a clockwise and an anticlockwise direction.

Saccadic movement is the movement employed when the eye moves rapidly from one location to the next. The patient with low vision still needs to undertake this movement when reading large print or using an electronic vision enhancement system (EVES; see Ch. 14). A tiled surface is very useful in this regard. The patient should fi xate on the tile straight in front of them. They should then fl ick the eyes from one perpendicular line of grouting to the next in both directions. Glancing sequentially from one ornament on the mantelpiece to the next or, when out of doors, looking from one railing to the next serves the same purpose.

Patients should be warned that these exercises may cause strain and muscular discomfort (it is the extrinsic muscles of the eye that are being exercised) in the early stages. It is important to assure the patient that these exercises are not harmful and that the symp-toms will diminish and quite quickly disappear altogether.

17.4 Eccentric vision

In Chapters 1–4 the causes of central vision loss were described. The majority of patients with central visual loss utilise eccentric fi xation relatively successfully, even without training, when under-

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taking tasks at far and intermediate distances. Their main diffi -culty arises when they attempt consciously to fi xate on specifi c objects at reduced working distances. This can be very apparent when interviewing a patient with, for example, macular degenera-tion. The patient may appear to look past you, over your head or shoulder, thus utilising the principle adequately whilst in conver-sation. This may, however, give rise to one of the social problems associated with central vision loss (see Ch. 19). When the patient tries to fi xate on a near object, such as trying to read with or without a LVA, the skills apparently utilised for distance vision are lost. This is why so many LVAs can end up in drawers, not only unused but creating a sense of failure in the recipients, making them believe that the diffi culty arises from their own shortcoming.7

To use eccentric fi xation effectively, the patient has to under-stand what eccentric viewing is and why it is useful. The best way to achieve this is to give the patient an understanding of how dif-ferent areas of the retina perform, followed by a practical demon-stration to fi nd which area(s), in each eye perform best for them. It should be explained that it is only at the centre of the retina, at the macula, that human beings have normal (6/6) [LogMAR 0.0] vision, which drops to approximately one-half of this resolution at 3° from the centre and to one-eighth at 6°, and that this deterio-ration in the power of resolution (acuity) continues across the retina past the area where we perceive colour, through the mono-chromatic area to where, at the very edge of our visual fi eld, only movement is discernable. Using, for example, the Eccentric Fixa-tion Chart (Fig. 17.2), the patient can be shown the angle and direction of eccentricity that they need to employ to achieve optimal vision.

When using this chart the patient with central visual loss is asked to look directly at the central target, which should disap-pear, and report which character or characters are the clearest. The distribution of letters and fi gures is so arranged that, when a par-ticular character is identifi ed as the clearest, the practitioner has to ask only whether it is in the upper or lower half, or to the right or left. If the patient’s acuity, or literacy, is such that they cannot identify the characters, they can be asked to report in which part of the chart characters appear darker or darkest.

This establishes the direction and angle of eccentricity required to achieve that patient’s best acuity. The patient can then be asked to fi xate centrally on an identical character diametrically

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opposite their chosen character; this character will now disappear into their area of no vision, and the central target should come into view.

This direction and angle of eccentricity holds for viewing any object at any distance. This test should be carried out for both binocular and monocular vision. The patient can now be trained to use eccentric viewing in any context.8

Utilising eccentric viewing when using an optical LVA is prob-ably the most diffi cult context in which to achieve success. When presented with a circular or rectangular aperture, the natural ten-dency is to want to look at, or through, its centre. The patient with low vision may need to ‘look’ towards, at, or even past the rim of the LVA to see what is at the centre – a most unnatural stratagem. The patient is more often than not an elderly person with normal viewing habits built up over a lifetime.6

Figure 17.2 Eccentric Fixation Chart.

Practical advice

• Try to form a picture of how the impaired vision has affected the person’s life.

• Empathy is better than sympathy.

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17.5 Optical LVAs and low vision therapy

The low vision therapist has three areas of input into the provision and use of optical LVAs. In brief, these are: to inform the patient about optical LVAs, to ensure that the patient can use the optical aids that have been prescribed, and to make sure that the patient has no outstanding tasks that could be assisted with an optical aid.

In the fi rst instance, if the patient has never attended a low vision clinic, the therapist should:

• Explain the important role that optical aids can play• Have a selection of optical aids available to demonstrate the

value and potential benefi ts to be derived from their use• With the patient’s consent, initiate the procedure for referral

to, and assessment at, a low vision clinic.

It is not the role of the therapist to prescribe or provide optical LVAs.

If the patient already has, or uses, an optical aid (and that dis-tinction can be a very real one), the role of the therapist is to help them use it optimally. Often, after training, performance would indicate a different or an additional aid, and a review appointment at the low vision clinic should be sought.

17.6 Group work and low vision therapy

With careful selection, there is value in undertaking some of the low vision therapy in a group setting. Most of the work described in this chapter can be undertaken with groups of up to six members. The experience of working with other people with similar prob-lems is often therapeutic in itself, and to fi nd out what other people with seriously impaired vision have been able to achieve can be helpful to each member of the group. Conversely, helping others who are less fortunate to achieve some degree of success can be both rewarding and encouraging. It creates an atmosphere of mutual encouragement within a relatively non-threatening envi-ronment. Having established in the group setting what is possible and what the potential is for the individual, it is often necessary to continue the work on a one-to-one basis. It should be remem-bered that personality, interest and motivation are factors that infl uence outcome.9

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Group work can be an effective and economical use of resources. The internal dynamics of a group play an important role in its potential for success, so some care and attention need to be paid to the selection of members. There is a strong temptation to believe that a group of people with similar pathology constitute a cohesive group. This is not necessarily the case: the stage of development of the disease process will be different, the degree of vision loss will be different, and individual needs and motivation may also be different. Tensions can arise when these differences are por-trayed against a background of apparent ‘sameness’ arising from the same pathology. Different disease processes and different types and levels of visual loss help to put the individual into a more realistic context.

Age is relevant only when the age range traverses generations. For example, the young adult in a group of elderly people may be pitied. This may disrupt the unity of the group, and the whole purpose of group work may be seriously undermined, or even totally lost.

Other sensory or physical disabilities do not, of themselves, cause any particular group work diffi culties. However, a seriously depressed person may not contribute positively to conventional group work. A person with below average learning ability may also fail to integrate comfortably into a conventional group.

Although most visually impaired people can benefi t from low vision therapy, some, because of their particular needs, may be able to take advantage of it only on a one-to-one basis. Referrals may come from other professionals, but assessment of the appro-priateness, or otherwise, of group work has to be made by the practitioner.

17.7 Brain damage and low vision therapy

The problems associated with visual dysfunction resulting from brain damage following strokes, road traffi c accidents or other traumatic incidents have, until recently, often been neglected by those responsible for medical and community-based rehabilita-tion. It has been accepted for some time that speech therapists, occupational therapists and physiotherapists can contribute to the improvement or restoration of functions impaired by a cerebrovas-cular accident (CVA). Low vision therapy may also have a contri-bution to make to the rehabilitative process of these patients.10

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For example, the patient attempting to relearn to read after expe-riencing a left homonymous hemianopia faces different problems from the person with a right homonymous hemianopia. Hemiano-pic fi eld loss may, in addition, be associated with visual neglect. The rehabilitative strategies used in these cases are more complex than those used in conventional hemianopic cases. Again, a person who looks at an object or an acuity chart and is unable to name the object or letter may not be suffering from loss of vision, but from a cognitive diffi culty that may be amenable to help.

Interest, knowledge and experience in this fi eld are growing, and patients with conditions such as hemianopia, visual agnosia, visual alexia and visual asthenia (Table 17.1) are now more likely to receive service from the world of rehabilitation.11,12 Similar chal-lenges arise when developing and delivering services to those who have moderate to severe learning disability. Testing and training materials need to be produced in user-friendly forms, and the need for skilled and experienced multiprofessional teamwork is a prerequisite for success.13,14

17.8 The family and low vision therapy

It is important to help the family understand the nature and value of residual vision. Having demonstrated to the patient that it is, for example, safe to go out on their own, the family also has to be convinced that it is safe. The patient must be allowed to use their residual vision. Likewise, within the home, family and friends must be encouraged to work with the visually impaired person to modify and adjust the environment to make tasks as easy as possible. In many cases adjustments made will be to the benefi t of everyone. Most importantly, family members must be dissuaded from doing everything for their visually impaired member, such as a child or elderly relative, as this can be demotivating and detrimental to the visually impaired person’s sense of independence.15

17.9 Summary

The role of low vision therapy in the context of rehabilitation is to write, as it were, a customised ‘user’s guide’ for each patient’s impaired vision. A user’s guide should include a simple

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explanation of the anatomy and physiology of the human eye and visual system. The methods of managing refractive errors must also be considered. The guide should also offer a simple explana-tion of the disease process that has resulted in the loss of vision and how the vision has been affected.

Low vision therapy involves the acquisition of good visual habits to enable patients to use their residual vision to better effect. For example, techniques for the use of eccentric vision, as well as

Table 17.1 Glossary of Ophthalmic Terms Associated with Cerebrovascular Accident14

Ophthalmic term Defi nition

Hemianopia Loss of vision in one-half of the visual fi eld

Homonymous When the loss of vision is on the same side ofhemianopia the visual fi eld in both eyes, such as the nasal half of one eye and the temporal half of the other. This results in total blindness in one-half of the visual fi eld, either to the right or to the left of the vertical median. The macula (high- resolution central fi eld) may be spared

Binasal or When the loss of vision is in both nasal (binasal) bitemporal halves of the visual fi eld or in both the temporalhemianopia halves (bitemporal)

Altitudinal When the loss of vision is in the upper half orhemianopia the lower half of the visual fi eld

Visual agnosia This describes the inability to recognise people or objects owing to disturbance in the association areas of the brain when the photoreceptors and visual pathways are intact

Visual alexia This form of visual agnosia describes the inability to recognise written words or letters. Often a patient recognises the fi rst letter in a word but will have forgotten it by the time the second letter is recognised. Similarly, with words, the previous word is forgotten by the time the next one is recognised

Visual asthenia This form of visual agnosia describes the fading of the cortical image before recognition can take place

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advice on the use of lighting and contrast, should be described. Low vision therapy should also provide training in the use of aids and appliances for vision enhancement, such as optical and elec-tronic magnifi ers, as well as encouraging the use of the other senses as vision substitutes. The issues surrounding frustration and depression need to be understood and addressed within the context of low vision therapy. There are advantages in doing some of this work in a group setting. It is also important to help the family understand the nature and value of residual vision.

References

1. Berg RV, Jose RT, Carter K. Distance learning techniques. In: Jose RT, ed. Understanding low vision. New York: American Foundation for the Blind; 1983:277–316.

2. Taylor RE, Upton LR. Stress and coping: implications for visual impairment. Journal of Vision Rehabilitation 1988; 2:23–28.

3. Adams OF. Assessment and prediction in rehabilitation. Proceedings of the Fifth European Regional Conference of Rehabilitation International; 1990:372–374.

4. Lindner H, Rinnert T, Behrens-Baumann W. Illumination conditions of visually impaired people under private domestic circumstances – clinical study on 91 patients. Klinische Monatsblatter fur Augenheilkunde 2001; 218:774–781.

5. Birch J. Diagnosis of defective colour vision. New York: Oxford University Press; 1993.

6. O’Connell WF. Eccentric viewing. In: Cole RG, Rosenthal RP, eds. Remediation and management of low vision. St Louis: Mosby-Year Book; 1996:27–58.

7. Waiss B, Cohen JM. Visual impairment and visual effi ciency training. In: Cole RG, Rosenthal RP, eds. Remediation and management of low vision. St Louis: Mosby-Year Book; 1996:59–70.

8. Adams OF. Using eccentric vision. New Beacon 1997; 953:4–6. 9. Adams OF. How the blind see. New Beacon 1985; 813:1–3; 814:41–

44; 815:73–77; 816:105–108. 10. Adams OF. Whose brain problem is it anyway? New Beacon 1993;

913:21–22. 11. Dutton GN. Cognitive vision, its disorders and differential

diagnosis in adults and children: knowing where and what things are. Eye 2003; 17:289–304.

12. Bradshaw JL, Mattingley JB. Disorders of object recognition: the agnosias and related phenomena. In: Clinical neuropsychology: behavioral and brain science. San Diego: Academic Press; 1995:83–123.

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13. Sacks O. The man who mistook his wife for a hat. South Yarmouth, MA: John Curley; 1986.

14. Lindsay J, McGlade A, Jackson AJ. Visual impairment and learning disability in adults. CE Optometry 2004; 7:63–67.

15. Ford M, Heshel T. The In Touch handbook, Sections C & I. Cardiff: In Touch Publishing; 1995.

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CHAPTER

Functional visual lossOwen F. Adams

181818

18.1 Introduction

The impact of visual impairment on the life of an individual is much more profound than can be quantifi ed by the simple mea-surement of visual acuity, visual fi eld and contrast sensitivity loss. Similarly, an assessment of the implications of visual impairment must be broader and deeper than a review of the diffi culties asso-ciated with mobility, reading and writing, or switching on the washing machine. Visual impairment impacts on every aspect of a person’s life. Ordinary, everyday social intercourse can, and usually does, present new diffi culties. Meeting people, whether socially or vocationally, is potentially stressful. Going out un-accompanied, going for a walk, shopping, visiting, being visited, even answering the door, can become tasks to be avoided. The demands of education or the workplace can seem insurmountable. Hobbies and sporting activities, which often constitute an impor-tant part of a person’s life, lose their appeal and are abandoned. The temptation to become a recluse can be overpowering.

18.2 The psychosocial dimension

Concern about what other people think is not something that most of us admit to, yet it is a potent factor infl uencing our behavi-our. Everybody wants to feel, and appear to be, competent and

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independent. Nobody enjoys situations in which they feel foolish, or appear to be incompetent or inept. Visual impairment con-stantly creates diffi cult situations that, in turn, precipitate a lack of self-confi dence. This is not so much an intrinsic characteristic of visual impairment as it is the result of how visually impaired people feel they are accepted, or seen, by other people. It is the same characteristic that the French philosopher and dramatist, Jean-Paul Sartre, described when he suggested that ‘Hell is other people’.1

As the vast majority of visually impaired people are aged over 65 years, and the causes are mainly age related, it is all too easy for others to associate ‘failing sight’ in the elderly with the normal ageing process. It is subsequently not recognised as a deeply emo-tional experience that has a very real potential to induce depres-sion. The depression can be intensifi ed by a feeling that ageing will continue to provide such devastating blows to the individual and that they are ‘wearing out’.

It does not matter whether the individual trying to cope is a child playing football or Scrabble, a young adult looking for a boyfriend or girlfriend, or an older person waiting for a bus. Their inability to cope with the visual demands of the situation in the presence of others is deeply damaging to their self-esteem. The experience is of particular signifi cance to the young adolescent who struggles with the already formidable problems of growing up.

Visual impairment does not, of itself, inevitably lead to severe clinical depression. Such an extreme response is, mercifully, rare; the form of depression more commonly encoun-tered is, however, no less real. Loss of a limb or loss of one of the senses has been likened to bereavement, and people are said to go through the same gamut of emotional responses. The visu-ally impaired are no different. Like the bereaved, they are very conscious of what it is they have lost, and feel alone in their grief.2

The relationship between the extent and duration of visual loss and the onset and resolution of depression is, however, complex, and individual responses vary signifi cantly.3–5 In a review of three groups of older, visually impaired patients, the prevalence of depression ranged from 32% to 40%. This compared with age-matched rates of between 14% and 20% in the general population.

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18Functional visual loss 1818

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Many visually impaired people avoid answering the doorbell because, when they open the door, they are often confronted by a silhouetted fi gure who just stands there unannounced. When they ask who it is and are told, often in a tone of voice implying they ought to know, understandably they feel embarrassed and hurt. Visually impaired people sometimes resent it when their friends or relatives forget their condition and expect behaviour from them that they cannot deliver. They may, for example, be accused by a friend of walking past them in the street without speaking. Ironi-cally, on the other hand, the over-helpful friend may offer the visually impaired person assistance that is not required. This, too,

18.3 The reactions of others

Much can be learned from an examination of some of the situa-tions that generate these feelings of uncertainty, anxiety or inade-quacy. The following examples are typical of the type of experience reported by visually impaired people within the ‘safe’ environ-ment of a group discussion or during the course of a counselling session.

An impairment of visual acuity will, for example, minimise the visual cues available to those seeking the attention of a shop assis-tant, bar-worker or receptionist. Because of reduced acuity, one woman reported that she could not see whether she had the atten-tion of the person behind the counter and subsequently waited to be approached. When she noticed that people who had come after her were being served, she asked for the service she wanted and was embarrassed on being told that she would have to wait her turn. Another common diffi culty in this context is that people using eccentric viewing appear to be looking elsewhere. The person behind the counter does not know they are being looked at and, therefore, ignores the apparently otherwise absorbed customer.

Practical advice

• Remember, your patient may have great diffi culty in reading your body language.

• Do your receptionist and other members of the practice team know how to identify and sensitively assist the visually impaired?

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can cause resentment, as the visually impaired person may feel their friend ought to know that they can manage that sort of manoeuvre on their own.

Incidents such as these are very discouraging, particularly to the newly visually impaired, and can easily precipitate a pattern of anxiety and inadequacy, with a tinge of resentment and bitterness. Good counselling skills, which are an important element of the rehabilitation programme, should help to ensure that the visually impaired person realises that, although they themselves are con-stantly aware of their loss, other people, however well intentioned, do forget at times. Allowances have to be made on both sides.

18.4 The social graces

There are certain activities in life, trivial enough in themselves, on which people set great store because they feel that they refl ect the ‘real’ person, the sort of person they are and the sort of person they wish to appear to others. For example, the visually impaired, particularly the elderly, are embarrassed, even humiliated, by poor handwriting because they associate this with poor character.6 In addition, as identifi ed in Section 18.3, recognition of people we meet is an important social grace. These activities are associated with personal dignity and self-respect.

There is a dichotomy surrounding the use of eccentric vision in a social context. Although eccentric viewing unquestionably helps the visually impaired to use their vision to best advantage, it does have a negative social dimension. People like others to look at them when they are speaking, as this signifi es that they are paying attention. If the visually impaired person is looking past or beyond the speaker, it can be disconcerting. Users of eccentric viewing need to be conscious of this and learn to direct their eyes at their companion from time to time, just to make them feel comfortable. Staring straight at a person for a long period of time can, however,

Practical advice

• Introduce yourself by name.• Introduce colleagues in a similar manner.

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be even more disconcerting. Visually impaired people forget, or may never have known, what normal visual behaviour is, and need to (re)learn the eye movements associated with it.

Another area of social concern is associated with eating. Many newly visually impaired people avoid eating in public because of diffi culties associated with locating food on their plate and the embarrassment of food falling over the rim of the plate on to the tablecloth without their noticing it (Fig. 18.1 [Plates 25 & 26]). Choosing well lit restaurants using non-patterned plates and high contrast meals can, of course, help to alleviate such problems. Developing a healthy, mature rapport with friends and, indeed, visually impaired colleagues can help to overcome this sort of potential problem sensitively.

18.5 Entoptic, phantom and other hallucinatory images

Many visually impaired people report ‘seeing’ objects that do not actually exist in the external world. These range from the all too familiar ‘fl oaters and fl ashing lights’ to the more elaborate experi-ences referred to as the Charles Bonnet syndrome.7–10 Patients react differently to these experiences. Some are upset or even fright-ened, believing that this may be the onset of mental illness. Others are intrigued or entertained by them. Many are loath to admit, or acknowledge, that they have these experiences in case others, including family members, think they are going insane. It is important that the patient is reassured about these phenomena: that they are common, normal and do not presage anything sinister. Again, as with many of the emotional aspects of visual impairment, the rehabilitation group is a rewarding atmosphere in which to air these experiences. It only needs one person to admit the phenomenon for others to say that they, also, have had similar experiences, but never liked to talk about them.

These images present with different characteristics and have various origins. ‘Floaters’ are, unquestionably, the most common form of entoptic image and their origins are well documented. Different images are, however, often experienced by people with central scotomas. Most of these patients, throughout the course of their normal everyday life, are unaware of non-seeing areas within their visual fi eld. Sometimes, these non-seeing areas become apparent when seen against a uniformly bland background, and

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A

BFigure 18.1 (Plates 25 & 26) Place setting as seen by someone with normal vision (A) and how it may be seen by someone with visual impairment (B).

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appear to be moving objects. The patient tries to focus on them with a view to identifi cation. It is not uncommon for people to say they have seen small animals such as cats or rodents moving about.

The most dramatic phantom or hallucinatory images are those initially attributed to Charles Bonnet, who in 1760 drew attention to the images described by his 89-year-old grandfather. These images can be quite elaborate in design, colour and content; the most telling characteristic is their clarity of detail. The patients who ‘see’ these images, being visually impaired, cannot possibly see in such detail, illustrating that they are not being ‘seen’ visu-ally. In these cases the brain seeks to interpret inappropriately created stimuli in terms of the physical world. They are sometimes seen as faces, or as people who are often physically deformed. On occasion, patients say they recognise long departed relatives, or scenes may be remembered from childhood.

Personal experience of the author suggests that stress and periods of non-attention are the two most common circumstances associated with the appearance of these unwanted images. Relax-ation and the conscious direction of visual attention are the best ways of dealing with them. Many of the relaxation techniques currently advocated for the alleviation of stress can help. Asking patients to redirect their point of fi xation and alter the plane of focus can reduce or eliminate these images. Patients with a poor attention span fi nd this more diffi cult. Many patients are, however, fascinated by these intricate images and fi nd it diffi cult to ignore them.

Reassurance that these phenomena are common and are not associated with ‘madness’ will, in most cases, relieve patient apprehension. The commonness of these phenomena should not, however, blind us to the possibility of the presence of a more serious neurological dysfunction. Any concern about the latter should initiate referral for neurological investigation.

Practical advice

When a patient confi des as to having experienced hallucinatory images, remember that they are taking a risk in telling you. Treat their comments seriously.

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18.6 Understanding low visual acuity

It would be hard to overstate the diffi culty, indeed the impossibil-ity, of explaining a sensory experience to those incapable of expe-riencing it for themselves. How can one explain what it is to feel, to hear, to see, to smell or to taste to someone without one of these senses?

It is equally impossible to describe vision to those who have never experienced it, and low vision is no different in this respect. The adventitiously visually impaired can appreciate and explain their new situation in comparison to how it used to be, but what they are describing is the result of the change in their functional vision; they are not describing their vision. The normally sighted will say, if asked what they can see, that they see everything and see it clearly. Patently they do not: they may see a range of hills in the far distance, but with no real clarity. They accept this as normal and understand that if they were closer they would see details that distance renders invisible. Similarly, the congenital myope will live quite happily with a chronic moderate loss of acuity, believing their vision to be normal until they are given spectacles or contact lenses that demonstrate the difference.

18.6.1 What low vision looks like

There have been many examples of efforts to illustrate how people with impaired vision actually see. The most common are specta-cles with lenses that have been doctored to represent the effects of the various pathologies, and illustrations in books that show pic-tures disfi gured to create the same effect. When fi eld loss is associ-ated with the pathology, it is often only this aspect of the condition that is represented. Areas of the lens are blackened in a pattern mirroring the damage to the retina, but the rest of the lens is still clear and this part of the image remains unaffected. This approach ignores the effects of reduced visual acuity and gives rise to, or perpetuates, the belief that a person with a central scotoma views a world from which the centre is missing, or a person with diabetic retinopathy sees a world with little bits missing throughout their visual fi eld.

The process by which we view and interpret the world is much more complex than this snapshot approach would suggest. To apply this snapshot approach universally would suggest that to

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represent how a normally sighted person sees would be to con-struct a picture in which only the centre is in good focus and full colour, where the clarity diminishes as the person moves away from the centre, to a point where both clarity and colour are lost and, beyond this to a blank area representing the very periphery of the visual fi eld where only movement is discernible. This is, of course, how normally sighted people do perceive the world, but because the healthy eye is constantly changing its point of fi xation they are not conscious of the graded quality of the vision from the centre to the periphery, and so the brain is able to present them with a continuous picture of good overall quality (Fig. 18.2 [Plates 27–32]). The snapshot approach ignores the important role played by constant eye movement in visual perception. It also ignores the role of the brain in visual perception. Research has shown that the brain compensates for the lack of data (scotoma) and presents the viewer with a complete image. The quality of that image will, however, be degraded if the scotoma is in the macular area.

18.6.2 Low visual acuity and fi eld loss

Experience shows that visually impaired people with slowly pro-gressive pathologies are usually conscious only of central visual loss. Patients with glaucoma, for example, may have lost a consid-erable amount of their visual fi eld without being aware of it. These patients rarely present with symptoms associated with fi eld loss, and presenting symptoms are much more likely to equate with diminished contrast sensitivity. Similarly, patients with monocu-lar vision or, indeed, with hemianopia are often wholly oblivious to their reduced fi eld of vision until some circumstance or event brings it to their attention. Those with hemianopia are often sur-prised to be told that the loss is binocular and that it is not simply loss in the eye on the hemiparetic side of the body. On the other hand, minimal central visual loss, or indeed metamorphopsia or distortion in an eye with normal good vision, when experienced suddenly is detected instantly and the patient complains of not being able to see properly. This is very evident in early age-related macular degeneration, when the patient complains of diffi culty in reading or reports that straight lines, such as lamp-posts or window frames, appear bowed or corrugated. Image distortion may also indicate conditions such as retinal tear, retinal pucker or retinal detachment.

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A

BFigure 18.2 (Plates 27–32) Real world scenes and how they may be seen by someone with visual impairment: street scene (A,B).

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C

DFigure 18.2 Continued Countryside view (C,D).

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E

FFigure 18.2 Continued Shop window (E,F), illustrating how diffi cult it may be to recognise the type of shop from the window display.

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G

HFigure 18.2 Continued Diffi culties encountered in a supermarket environment (G,H).

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Acuity is to do with object size, detail and viewing distance. Often, both resolution and recognition are required. A person with low visual acuity is able to see, or recognise, an object at a very much shorter distance than a person with normal vision would see or recognise it. This also means that an object may be seen at one distance but may be recognised only at a much shorter distance. In practical terms, this may mean being able to see a building but not a person standing at the entrance, or a range of hills but not individual fi elds, or a person on the other side of the street, but not someone standing at the end of the street. The most appropriate way, therefore, to illustrate this sort of vision is to make the smaller objects imperceptible or indistinguishable, not to obliterate whole areas of the picture.

18.7 Summary

Visual impairment impacts on every aspect of a person’s life. An inability to cope with the visual demands of a given situation in the presence of others can be deeply damaging to a person’s self-esteem and personal dignity.

There are many situations in which the person with impaired vision is at a disadvantage: meeting people, whether socially or vocationally, going out unaccompanied, going for a walk, shopping, visiting, having visitors, even answering the door. The visually impaired often feel offended when friends or rela-tions forget their disability, and this can lead to resentment and bitterness. They, also, need to learn to make allowances for others.

Many visually impaired people experience entoptic or phantom images. These range from the all too familiar ‘fl oaters’ to more elaborate complex images referred to as the Charles Bonnett syn-drome. Relaxation, the conscious redirection of visual attention, and reassurance that these phenomena are common and not a sign of ‘madness’ will help the patient experiencing these phenomena, and the family, to cope.

Fundamental to the process of helping the visually impaired to cope is an understanding of what it is like to experience visual impairment. Normally sighted practitioners should make every use of realistic methods of illustrating and simulating visual loss.

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References

1. Sartre J-P. Huis clos. Paris: Gallimard; 1945. 2. Dodds AG, Bailey P, Pearson A, Yates L. Psychological factors in

acquired visual impairment: the development of a scale of adjustment. Journal of Visual Impairment and Blindness 1981; 75:306–310.

3. Karlsson JS. Self-reports of psychological distress in connection with various degrees of visual impairment. Journal of Visual Impairment and Blindness 1998; 92:483–490.

4. Teitelbaum LM, Davidson PW, Gravetter HA, Taub HS, Teitelbaum CS. The relation of vision loss to depression in older veterans. Journal of Visual Impairment and Blindness 1994; 88:253–257.

5. Horowitz M, Reinhardt JP. Depression among low vision elders. In: Stuen C, Arditi A, Horowitz A, Land MA, Rosenthal B, Seidman K, eds. Vision rehabilitation: assessment, intervention, and outcomes. Amsterdam: Swets and Zeitlinger; 1999:655–658.

6. Ford M, Heshel T. The In Touch handbook, Section F18. Cardiff: In Touch Publishing; 1995.

7. Lepore FE. Spontaneous visual phenomena with visual loss: 104 patients with lesions of the retinal and neural pathways. Neurology 1990; 40:444–447.

8. Damas-Mora J, Skelton-Robinson M, Jenner FA. The Charles Bonnet syndrome in perspective. Psychological Medicine 1982; 12:251–261.

9. Jacob A, Prasad S, Boggild M, Chandrate S. Charles Bonnet syndrome – elderly people and visual hallucinations. British Medical Journal 2004; 328:1552–1554.

10. Menon GJ, Rahman M, Menon SJ, Dutton GN. Complex visual hallucinations in the visually impaired: the Charles Bonnet syndrome. Survey of Ophthalmology 2003; 48:58–72.

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19.1 Introduction

Every professional who comes into contact with a visually impaired person should be conscious that there are other professionals who may be in a position to make an important, even major, contri-bution to the quality of the service offered to that patient. A review of the links that exist between low vision service providers in the UK and other professionals found wide variations in the nature and level of collaboration.1 The implication was that interprofes-sional awareness training and evaluation is required in this area. The need for a multidisciplinary holistic approach to low vision service delivery has, in addition, been highlighted in the UK by the Low Vision Consensus Group, whose fi ndings are now universally accepted as a template for good practice.2

The number of disciplines that may be involved with a patient at any given time can vary greatly. Patients with age-related macular degeneration (AMD), for example, may have all their ophthalmic needs met by an optometrist or ophthalmologist. Patients with hereditary disorders, such as retinitis pigmentosa, would also benefi t from the advice of a geneticist, whereas the diabetic patient needs the services of the metabolic physician. The need for intraprofessional referrals such as these are easily recog-nised, and are usually made as a matter of course. The need for other interdisciplinary referral to professionals, such as rehabilita-

CHAPTER

Rehabilitation: a multidisciplinary approachOwen F. Adams

191919

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19Rehabilitation: a multidisciplinary approach 1919

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tion workers, social workers, audiologists, occupational therapists and low vision therapists, is not always so obvious, or so predictable.

The list of disciplines that may contribute to patient manage-ment is impressive – if not daunting. From the medical profession there is the general practitioner, ophthalmologist, ENT specialist, neurologist, metabolic physician, paediatrician, geriatrician, psychiatrist and geneticist; there is the practice nurse in the primary care team, the district nurse, hospital ophthalmic nurse, diabetic nurse and psychiatric nurse, as well as those professions allied to medicine such as the optometrist, orthoptist, physiothera-pist, occupational therapist, speech therapist, hearing therapist and audiologist. In addition, there are those other professionals such as the chiropodist, dietician, psychologist, rehabilitation worker, low vision therapist, social worker, disabled employment adviser, social security benefi ts offi cer, education adviser and teacher.

Naturally, no one patient will require the services of all the above, but many would benefi t from the services of some at one time or another. It is important, therefore, that professionals have a clear idea of the contribution they themselves are capable of making and of the contribution that others might make. It is equally important that they have a sound understanding of the particular expertise of the other professions and the reasons for which they may wish to involve them, as well as the method of making such referrals. This is the basis of a sound multi-disciplinary approach to patient management. The purpose of involving another professional is so that, when a patient has been identifi ed as having a need that is not, and cannot be, met by the person who identifi ed it, a referral can be made to a professional colleague, perhaps from another discipline, with more relevant knowledge or experience. This underlines the necessity for both good intradisciplinary and interdisciplinary awareness and understanding.

Early examples of the recognition of the need for good inter-disciplinary and intradisciplinary relationships were the estab-lishment of the Kooyong Low Vision Clinic in Melbourne, Australia, in 19723 and the Center for the Partially Sighted in Santa Monica, California, in 1976.4 Within the UK there are a number of models, each utilising these principles. For example, there is the Royal National Institute of the Blind (RNIB), Camden and Islington centre at Judd Street, London,5 the Bristol Low Vision

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Project at the Royal Eye Hospital, Bristol6 and the Salisbury Sight Centre at the District Hospital in Salisbury.7 In Scotland there is the low vision service based in the Fife Sensory Impairment Centre, Kirkcaldy.8 In Wales there is the recently launched National Low Vision Service based in Cardiff,9 and in Northern Ireland the Regional Low Vision Service at the Royal Victoria Hospital, Belfast.10

19.2 Intradisciplinary and interdisciplinary referrals

Within hospitals and between hospitals, as well as within primary care teams, referrals between medical and associated profession-als are usually routine. The patient with diabetic retinopathy is usually seen by the diabetic nurse, dietician and chiropodist, as well as by the metabolic physician. Within the ophthalmic depart-ment they may be seen by the ophthalmologist, ophthalmic photographer, orthoptist, optometrist and those providing in-house low vision services. Similarly, the patient with a cerebrovas-cular accident (CVA) will be referred by the physician to the occupational therapist and physiotherapist, and, if necessary, to the psychologist.

Institution-based professionals need to also be aware of the community-based services that may benefi t patients on discharge from their care. Ideally, such links will have been established well before the time of discharge. Social service departments and local societies provide a range of social and rehabilitation programmes, as outlined in the earlier chapters of this section, which patients can access to their advantage. The disabled em-ployment advisory service fulfi ls an important role for patients of working age. The involvement of the Disabled Employment Advisor (DEA) is, however, dependent upon the receipt of good information and support from the ophthalmologist, optometrist, orthoptist, audiologist, rehabilitation worker and the various therapists who may be involved (occupational, physiotherapy, speech, vision and hearing). Education advisory services are equally relevant to children and young adults, and are also de-pendent upon good interdisciplinary support and information. The importance of involving both parent and teacher cannot be overemphasised.

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Every time a patient meets a professional for the fi rst time expecta-tions are created, and if a further referral is made new expecta-tions will be added. These expectations are based on the patient’s knowledge of that profession and their understanding of the reasons for which the referral was made. A truly multidisciplinary service can be provided only if each professional involved takes a holistic approach to the patient and if there has been good quality communication and exchange of information between the dif-ferent professions and agencies. The need for a coordinator, or key worker, in the multidisciplinary context should be considered. The particular professional who would be the most appropriate will depend upon the needs of the patient and which professions are actively involved at any particular time. A low vision ‘passport’ containing key information recorded by each professional who has previously contributed to the rehabilitation of the patient can also assist, while keeping the patient informed and ‘involved’ in their rehabilitation.

Practical advice

• Consider what other needs your patient may have and who might be able to meet them.

• Inform yourself about other local agencies and the services they provide.

Practical advice

• Satisfy yourself that your onward referrals have been attended to. Ask for an acknowledgement and/or report.

• Make sure that, when there is input from a range of individuals, professionals and agencies, a case coordinator oversees the entire rehabilitation process.

• Although a well integrated, multidisciplinary service is in the best interests of the patient, confi dentiality and consent are important factors to bear in mind. Clinical and personal details about a patient should be sought, or given, only with the express permission of the patient involved.

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19.3 The patient’s expectations

In many cases the fi rst professional that the visually impaired person will consult is an optometrist. This will be done with the very reasonable expectation of being prescribed corrective spec-tacles, or contact lenses, to enable the patient to see clearly again. It is often at this stage that early indicators of possible pathology are identifi ed and, if deemed necessary, referral is made to the hospital ophthalmic service, perhaps through the patient’s general practitioner. Patients should expect the referral to be processed within a reasonable timescale. When the patient gets to the hospi-tal, they will expect to be seen without unnecessary delay and to enjoy a certain degree of privacy during the consultation.

By this time the patient’s imagination has probably gone into overdrive. The optometrist may have said that spectacles or contact lenses are not going to help, and the family doctor will have said it’s a case for an eye specialist at the hospital. When the patient visited the original referring optometrist, the expectation will have been that of one who needed spectacles and, as such, the event will have been expected to be relatively stress free. This new referral to a hospital consultant will create expectations of a dif-ferent order, depending on the reason given for the referral and the patient’s previous experience of hospitals. Expectations may also be coloured by folklore about eyes and going blind. This visit is unlikely to be stress free. For that reason, patients should not only be permitted, but actively encouraged, to bring someone with them to the hospital appointment and for this person to be present during the consultation. The information being given, particularly at this fi rst appointment, is often news that people do not expect and are unable fully to understand, let alone assimilate. They are often so shocked, even frightened, by what they are being told that they are unable to listen intelligently to the rest of the information or diagnosis, prognosis and/or proposed treatment. Although the language used is often, inevitably, alien to most patients and their friends, they will have taken in that there is something seriously wrong and that, although some treatment may be offered, they should not expect a cure.

From this point onward, referrals to the non-medical profes-sionals can be only for help in coping with the situation and should not create unreasonable expectations. Experience shows that referral to the low vision clinic, for example, is often offered

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in terms that give patients the impression they will be able to read again, albeit with new ‘special’ spectacles. This is often interpreted as being able to pick up a newspaper and reading it in the way in which they were accustomed. Such expectations can only end in disappointment.

19.4 Every professional’s expectations

Every professional meeting a referred patient for the fi rst time has the right to expect that the patient has been told about the referral. For example, where the contact is a domiciliary visit or the sending out of an appointment, an unexpected call can be a bad start to any new relationship. The professional also has the right to expect the patient to have been given a reasonable explanation of the purpose for the referral and a general indication of the type of service that might be offered. It is equally important that the refer-ring professional should indicate those tasks, or issues, that need to be addressed without prejudging the precise service that the patient will receive. It is for each professional to make the relevant professional assessment of the patient’s needs and to decide whether, and how, they might meet those needs.

Every professional has the right to expect that each patient who may benefi t from their services is given the choice and opportu-nity to access them. This is best achieved when everyone involved has a good understanding of the skills and knowledge base of other professions. Good cooperation and coordination between professions, and the provision of periodic awareness modules as part of professional in-service training programmes, are essential in this respect. The recognition of different expertise in the world of medicine and allied professions is already well defi ned and relatively straightforward. It is in the community-based services where blurring of roles and areas of work may be less well defi ned or understood.

Every visually impaired person is entitled to a proper assess-ment of need and to have those needs met by the appropriate qualifi ed professional. The rehabilitation worker, for example, cannot operate as an amateur optometrist, or as a social worker. Equally, although the ‘problem’ family with a visually impaired member may need the attention of a qualifi ed social worker, the ‘normal’ family with a visually impaired member does not. The patient who has sustained a CVA may be in need of the attention

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of the physiotherapist, occupational therapist and low vision thera-pist, as well as the rehabilitation worker, psychologist and social worker. The audiologist should expect to be given the opportunity to assess the visually impaired person with a hearing loss, however slight.

19.5 The voluntary sector

Alongside the many professions and organisations referred to in this chapter that might be involved in the delivery of a rehabilita-tion programme, there is a wider range of people and organisa-tions that provide a variety of goods and services for people with a visual impairment.

The voluntary sector includes the family member, friend or neighbour, who provides a free and virtually invisible service by doing such things as reading mail, shopping and offering trans-port, at one end of the spectrum, to the more high profi le national organisations with large budgets that employ paid executives and administrators, at the other. Between these is a plethora of organi-sations working locally or regionally, addressing a wide variety of needs and interests. All of these organisations depend on the goodwill of the individual volunteer. What follows is an overview of the great range of organisations that exist, and the range of services they provide, together with some examples of the various types of society. The named societies have been chosen randomly to illustrate the different types of body within the voluntary sector. A list of the main organisations is provided in the Appendix.

19.5.1 Individual volunteers

There is a vast army of people who, on a voluntary basis, offer their time, skills, knowledge and experience to assist in the cre-ation and provision of a particular service for visually impaired people. They include the often ignored man or woman holding a

Practical advice

The hallmark of a good professional is knowing one’s own skills and limitations, and recognising the skills specifi c to others.

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collection box at the entrance of stores and supermarkets, or drop-ping those collection envelopes through letter boxes; the people who unfailingly organise, or read for, the local talking news-paper; those who become puppy walkers for the guide dog train-ing kennels; the professional and non-professional men and women who serve on the management committees of voluntary organisations, both small and large, locally and nationally. There are also the people who provide a more direct and personal service, such as a befriending service, by calling on lonely or isolated visu-ally impaired people, either in person or by telephone, or who offer a free taxi service to hospital appointments or to assist in shop-ping. In a climate where governments look, increasingly, to the voluntary sector to augment, and in some cases deliver, the statu-tory service, the contribution made by volunteers is essential and their value incalculable.

19.5.2 Local societies

Most counties and cities, and many towns, have an association, society or club involved in some aspect of service for blind or partially sighted people. Examples of these are the Surrey Associa-tion for Visual Impairment, the Dundee Society for Visually Impaired People and the Leeds Jewish Welfare Board. In some cases the service is regional, covering more than one county or town, such as the Blind Centre for Northern Ireland or Merthyr Tydfi l and Mid Wales Institute for the Blind.

Many of the county and city societies started life as charitable or benevolent foundations during the nineteenth century, and offered the opportunity of employment in what were known as workshops for the blind. Because the crafts practised in those institutions, such as chair caning, basket making and brush making, are no longer economically viable, these workshops have either closed or turned to the manufacture of other products such as beds and mattresses, furniture and leather goods, the packag-ing industry, or they have been absorbed into government-led employment enterprises for the generally disabled.

As already stated, many local societies now deliver the statutory service in conjunction with the county or city social services department, as well as providing other types of support such as day centres catering exclusively for blind and partially sighted people. Other, smaller organisations offer other forms of support; it may be a social club, often organised on a self-help basis, and

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sometimes arising from some common interest such as a particu-lar pathology, or pursuit such as a sport or other recreational activity; a local talking newspaper enterprise; or a local branch of a national organisation, such as is described in Section 19.5.3.

19.5.3 National organisations

The national organisations fall into two broad areas: those that are service specifi c and those that are pathology specifi c. The former include such organisations as the Royal National Institute of the Blind (RNIB) and the National Council for the Blind of Ireland (NCBI).

The RNIB offers in excess of 60 different services and is the largest service provider for people with serious sight loss through-out the UK. It provides information, support and advice on all aspects of visual impairment; maintains and manages Braille and tape libraries, including the talking book service; and offers support in the fi elds of employment, education and recreation. A wide range of specialist equipment is available through RNIB resource centres. The NCBI offers a similar range of services in the Republic of Ireland.

The British and Irish Guide Dogs for the Blind Associations (BGDBA or IGDBA) cater mainly for the mobility needs of the visually impaired, and the Partially Sighted Society (PSS) provides a range of goods and services to cater for the needs of the visually impaired person.

The pathology-specifi c organisations are motivated by an inter-est in a specifi c disease process or group of pathologies such as retinal dystrophy, age-related maculopathy, retinitis pigmentosa and diabetic retinopathy. They can provide a forum for people with the same pathology, offering support and advice to newly affected people and their carers. They also fundraise in support of research programmes into the treatment and possible cure of these diseases and disorders.

Alongside the above there are organisations that act as umbrella bodies for groups of associations and societies with similar objec-tives, to provide a common forum and a common lobby in pursuit of their common interest. The National Association of Local Soci-eties for Visually Impaired People (NALSVI) is such a body, as is OPSIS (the National Association for the Education, Training and Support of Blind and Partially Sighted People), which performs a similar function on behalf of a number of organisations involved

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in the education and employment of the visually impaired. There are also many disability and age focused organisations that work in partnership with vision-specifi c organisations.

19.6 Summary

Every professional should be conscious that there are other profes-sionals who may be in a position to make an important, even major, contribution to the quality of the service that is offered to a patient. They should have a clear idea of the contribution they themselves can make, and a sound understanding of the particu-lar expertise of the other professions they may wish to involve. This is the basis of a sound multidisciplinary approach to patient management.

The need for intraprofessional referrals is easily recognised and usually made as a matter of course. The need for interdisciplinary referral is not always so obvious. Referrals between hospital-based medical and paramedical professionals are usually routine. There is also a need to think of the community-based services.

Every professional receiving a referral has the right to expect that the patient has been told about the referral and the reason for which it was made. The referring professional should not prejudge the precise service that the patient will receive.

Every profession has the right to expect that every patient who requires its services is given the opportunity to access them. Every visually impaired person is entitled to a proper assessment of need and to have those needs met by the appropriate qualifi ed professional.

The key to a successful multidisciplinary approach is that every professional knows his or her role and that their role is also known to every other professional involved. The hallmark of a good professional is knowing one’s own skills and limitations, and recognising those of others.

Practical advice

Think of the voluntary sector. Find out what societies and clubs for the visually impaired operate in your area. Would your patient benefi t from their services?

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There is a wide range of people and organisations that provide a variety of goods and services for people with a visual im-pairment; a knowledge of these is needed by those involved in providing low vision services.

References

1. Ryan B, Culham LE, Hill AR et al. Multidisciplinary low vision services in the United Kingdom. In: Arditi A, Horowitz A, Land MA, Rosenthal B, Seidman K, eds. Vision rehabilitation: assessment, intervention, and outcomes. Amsterdam: Swets and Zeitlinger; 1999:542–545.

2. Low Vision Consensus Group. Low vision services: recommendations for future service delivery in the United Kingdom. London: RNIB; 1999.

3. Lawrence M. Low vision care – the Kooyong experience. Journal of Visual Impairment and Blindness 1985; 79:337–340.

4. Genensky SM. The Carel C. Koch award lecture 1988: understanding and respect: a formula that really works. Optometry and Vision Science 1989; 66:336–338.

5. Rughani S. Advances in low vision care. New Beacon 2005; April:34–39.

6. Giltrow-Tyler JF. The Bristol Low Vision Project: a multi-disciplinary approach. Optometry Today 1988; 4 June:352–354.

7. Humphry RC. A new model of service. OCULUS Supplement 1995; March–April:1–8.

8. Hinds A, Sinclair A, Park J, Suttie A, Paterson H, Macdonald M. Impact of an interdisciplinary low vision service on the quality of life of low vision patients. British Journal of Ophthalmology 2003; 87:1391–1396.

9. Margrain TH, Ryan B, Wild JM. A revolution in Welsh low vision service provision. British Journal of Ophthalmology 2005; 89:933–934.

10. Lindsay J, Bickerstaff D, McGlade A, Toner A, Jackson AJ. Low vision service delivery: an audit of newly developed outreach clinics in Northern Ireland. Ophthalmic and Physiological Optics 2004; 24:360–368.

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Some useful contacts

England

Action for Blind People

14–16 Verney RoadLondon SE16 3DZTel: 0207 635 4800Fax: 0207 635 4900Email: [email protected]

Website: www.afbp.org

British Guide Dogs for the Blind

Head Offi ceHillfi eldsBurghfi eld CommonReading RG7 3YGTel: 0118 983 5555Fax: 0118 983 5433Email: [email protected]

Website: www.guidedogs.org.uk

Appendix

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Appendix

352

British Retinitis Pigmentosa Society (BRPS)

PO Box 350Buckingham MK18 1GZTel: 0128 082 1334Fax: 0128 081 5900Email: [email protected]

Website: www.brps.org.uk

CALIBRE Audio-Library

Aylesbury HP22 5XQTel: 0129 643 2339Email: [email protected]

Website: www.calibre.org.uk

Deafblind UK

National Centre for DeafblindnessJohn and Lucille van Geest PlaceCygnet RoadHamptonPeterborough PE7 8FDTel: 0173 335 8100 (voice/text)Fax: 0173 335 8356Text: 0173 335 8858Email: [email protected]

Website: www.deafblind.org.uk

Diabetes UK Central Offi ce

Natasha Lawrence, Acting Head of Community Fundraising10 ParkwayLondon NW1 7AATel: 0207 424 1000Email: [email protected]

Henshaw’s Society for Blind People

John Derby House88–92 Talbot RoadOld TraffordManchester M16 0GSTel: 0161 872 1234Fax: 0161 848 9889Website: www.hsbp.co.uk

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353

National Association of Local Societies for Visually

Impaired People (NALSVI)

21 Greencliffe DriveYork YO30 6NATel/Fax: 0190 467 1921Email: [email protected]

National Library for the Blind

Far Cromwell RoadBredburyStockport SK6 2SGTel: 0161 355 2000Fax: 0161 355 2098Website: www.nlb-online.org

Opsis (Working with Blind and Partially Sighted People)

c/o Queen Alexandra CollegeCourt Oak RoadHarborneBirmingham B17 9TGTel: 0121 428 5037Fax: 0121 428 5035Website: www.opsis.org.uk

Partially Sighted Society

PO Box 322Doncaster DN1 2XATel: 0130 232 3132Email: [email protected]

Royal London Society for the Blind

Dorton HouseSealSevenoaks TN15 0EDTel: 0173 259 2500Fax: 0173 259 2506Website: www.rlsb.org.uk

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354

Royal National College for the Blind

College RoadHereford HR1 1EBGeneral enquiries: 0143 226 5725Textphone: 0143 227 6532Programme helpline: 0143 237 6621Fax: 0143 237 6628Website: www.rncb.ac.uk

Royal National Institute of the Blind (RNIB)

105 Judd StreetLondon WC1H 9NETel: 0207 388 1266Helpline: 0845 766 9999 (Mon–Fri 09.00–17.00 hours)Textphone: 0800 085 3210Fax: 0207 388 2034Website: www.rnib.org.uk

RNIB Customer Services

PO Box 173Peterborough PE2 6WSTel: 0845 702 3153Textphone: 0845 758 5691Fax: 0173 337 1555

Royal National Institute for Deaf People (RNID)

19–23 Featherstone StreetLondon EC1Y 8SLTel: 0207 296 8000Textphone: 0207 296 8001Infoline: 0870 605 0123 or 0808 808 0123Textphone infoline: 0870 603 3007 or 0808 808 9000Fax: 0207 296 8199Website: www.rnid.org.uk

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355

Sense (National Deafblind and Rubella Association)

11–13 Clifton TerraceFinsbury ParkLondon N4 3SRTel: 0207 272 7774Textphone: 0207 272 9648Fax: 0207 272 6012Website: www.sense.org.uk

St Dunstan’s

12–14 Harcourt StreetLondon W1H 4HDTel: 0207 723 5021 (Mon–Fri 07.00–19.00 hours)Fax: 0207 262 6199Website: www.st-dunstans.org.uk

Scotland


Dundee RoadForfarAngus DD8 1JATel: 0130 746 3531Fax: 0130 746 5233Email: [email protected]


Deafblind Scotland

21 Alexandra AvenueLenzieGlasgow G66 5BGTel: 0141 777 6111 (voice/text)Fax: 0141 775 3311Email: [email protected]

Website: www.deafblindscotland.org.uk

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356

Diabetes UK, Scotland

John Fyfe, National FundraiserSavoy House140 Sauchiehall StreetGlasgow G2 3DHTel: 0141 332 2700Email: [email protected]

RNIB Scotland Resource Centre

Dunedin House25 Ravelston TerraceEdinburgh EH4 3TPTel: 0131 311 8521Fax: 0131 311 8529

RNID Scotland

54a FountainbridgeEdinburgh EH3 9PTTel: 0131 478 7800Textphone: 0131 478 7803Fax: 0131 478 7804

Sense Scotland

5th Floor45 Finnieston StreetClydeway CentreGlasgow G3 8JUTel: 0141 564 2444Textphone: 0141 564 2442Fax: 0141 564 2443

Wales

Diabetes UK, Cymru

Joseph Cuff, National FundraiserQuebec HouseCastlebridgeCowbridge Road EastCardiff CF11 9ABTel: 0292 066 8276Email: [email protected]

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357

RNIB Cymru Resource Centre

Trident CourtEast Moors RoadCardiff CF24 5TD.Tel: 0292 045 0440Fax: 0292 044 9550

RNID Cymru

3rd Floor33–35 Cathedral RoadCardiff CF11 9HBTel: 0292 033 3378Textphone: 0292 033 3036Fax: 0292 033 3035

Sense Cymru

5 Raleigh WalkBrigantine PlaceAtlantic WharfCardiff CF10 4LNTel: 0292 045 7641Textphone: 0292 046 4125Fax: 0292 049 9644

Wales Council for the Blind

Shand House20 Newport RoadCardiff CF1 2YBTel: 0292 047 3954Fax: 0292 045 5710Website: www.wcb-ccd.org.uk

Northern Ireland

Blind Centre for Northern Ireland

70 North RoadBelfast BT5 5NJTel: 0289 050 0999Fax: 0289 065 0001Email: [email protected]

Website: www.bcni.co.uk

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15 Sandown Park SouthKnockBelfast BT5 6HETel: 0289 047 1453Fax: 0289 065 5097Email: [email protected]


Deafblind UK

Northern Ireland BranchCourse Lodge10 Coilhill RoadKillyleaghCo. Down BT30 9STTel: 0284 482 1983 (voice/text)Email: [email protected]

Diabetes UK, Northern Ireland

Bryan Walliker, National FundraiserBridgewood HouseNewforge Business ParkNewforge LaneBelfast BT9 5NWTel: 0289 066 6646Email: [email protected]

RNIB Northern Ireland Resource Centre

40 Linenhall StreetBelfast BT2 8BGTel: 0289 032 9373Fax: 0289 027 8119

RNID Northern Ireland

Wilton House5 College Square NorthBelfast BT1 6ARTel: 0287 127 1750 or 0287 137 4619Textphone: 0287 127 1840Fax: 0287 127 1750

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Sense Northern Ireland Branch

Muriel and Tom Mathers11 The CoachesBrown BraeCroft RoadHolywood BT18 OLETel: 0289 042 1475

Republic of Ireland

Diabetes Federation of Ireland

76 Lower Gardiner StreetDublin 1Tel: 01 836 3022Fax: 01 836 5182Helpline: 185 090 9909Email: [email protected]

Website: www.diabetes.ie

Fighting Blindness

1 Christchurch HallHigh StreetDublin 8Tel: 01 709 3050Fax: 01 709 3010Email: info@fi ghtingblindness.ie

Website: www.fi ghtingblindness.ie

Irish Guide Dogs for the Blind

National Headquarters and Training CentreModel Farm RoadCorkTel: 021 487 8200LoCall: 185 050 6300Fax: 021 487 4152Email: [email protected]

Website: www.guidedogs.ie

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National Council for the Blind of Ireland

Whitworth RoadDrumcondraDublin 9Telephone: 01 830 7033Save Phone: 185 033 4353Fax: 01 830 7787Website: www.ncbi.ie

National Disability Authority

25 Clyde RoadDublin 4Tel/Minicom: 01 608 0400Email: [email protected]

Web: www.nda.ie

AP-H1815.indd 360 9/15/2006 1:31:23 PM

361

Index

A

A655 registration form, 5Abetalipoproteinaemia (Bassen–

Kornzweig syndrome), 49, 50Acceptance of loss of vision, 107–108Accommodation, 190–191, 224

age-related changes, 190with hand magnifi er use, 198,

199–200, 202with stand magnifi er use, 212

vergence of light, 214–215Achromatopsia, 161Activities of Daily Living Scale

(ADLS), 173, 174Acuity reserves, 147Adaptive equipment, 274Adolescents, visual impairment, 46–47

social problems, 326Age Blindness Burden, 13–14Age-Related Eye Disease Study

(AREDS), 86Age-related macular degeneration, 9,

13, 77, 78, 80–87, 107, 117, 313, 340, 348

aetiology, 78cataract, 89choroidal neovascularisation, 80, 81,

82, 83, 84classical membranes, 84, 86occult membranes, 86

clinical features, 78, 80dietary factors in progression

reduction, 86drusen, 78, 80, 84

management pathways, 81dry (atrophic) form, 78, 80

geographic atrophy, 80, 86epidemiology, 21fl uorescein/indocyanine green

angiography, 82–83, 86genetic factors, 78, 83–84information for patients, 309laser photocoagulation, 83, 84

physiological change, 79registration data, 19

rehabilitation services, 295retinal pigment epithelium

detachment, 82symptoms, 80, 333treatment, 84–86visual hallucinations, 82visual prognosis, 86, 87wet (exudative) form, 78, 80, 81–82,

84Age-related visual impairment,

77–100, 326associated depression, 326epidemiological data

global, 14population-based, 20–21

INDEX-H1815.indd 361 9/15/2006 1:34:05 PM

Index

362

registration data, UK, 20treatable causes, 21see also Elderly patients

Ageing-related changesaccommodation, 190visual physiology, 78, 79

Albinism, 9, 28, 33, 36, 37, 40, 74discomfort glare, 161low vision aids, 51

Allowances (Income tax, etc, Attendance), 303–304, 305

Alzheimer’s disease, 99Amaurosis fugax

central retinal artery occlusion, 97, 98

temporal arteritis, 94AMPPE, 71, 72Amsler charts, 85, 155Anger, response to loss of vision, 106Angular enlargement, 192–193Aniridia

discomfort glare, 161lighting requirements, 313

Anosmia, 49Anterior chamber paracentesis, 97Anterior ischaemic optic neuropathy,

98differential diagnosis, 96

Anti-vascular endothelial growth factor aptamer, 86

Aphakiachildren, 51contact lenses, 126

Aplanatic Comfort, 233Arc perimetry, 155Arden grating test, 141, 145Arthritis, 99Aspheric spectacle magnifi ers,

234–239Coil Hyperoculars, 234, 235, 238Coil ready-made hyperoculars, 235,

236Keeler systems, 235–239

Assessment of Visual Function Related Quality of Life Questionnaire (VFQOL), 173, 174

Astigmatism, 120Astronomical (Keplerian) telescopes,

242

enlargement, 245exit pupil, 250, 251length, 244, 246, 247, 248optics, 241–243viewing non-distant objects, 248

Attendance Allowance, 304Attitudes

of patients, 105, 109, 110–112, 327–328

response to loss of vision, 105–108, 294, 301, 326

of practitioners, 104of public, 104–105, 327

Audible thermometers, 277Audiologists, 340, 341, 342, 346Autofocus telescopes, 254Automated perimetry, 155

B

Back vertex power, hand magnifi ers, 199

Bailey–Lovie charts, 132–133, 134acuity, 124design characteristics, 131low contrast, 143, 145word reading, 149, 152

Bar magnifi ers, 218–222advantages/disadvantages, 219enlargement calculation, 219, 221fi eld of view, 221patient instruction, 222

Base-in prism, 125binocular spectacle enlargement,

228, 229, 230Bassen–Kornzweig syndrome

(abetalipoproteinaemia), 49, 50BD8 registration form, 5Befriending service, 347Behavioural problems, 36Behr’s syndrome, 35Benefi t entitlement, 2, 4, 6, 7Bereavement process, 109Bereavement response, 105–108, 294,

301, 326Best’s disease (vitelliform dystrophy),

42–43, 46, 50Biette’s retinopathy, 44Bifocal high-powered additions,

233–234Bifocals prescription, 125

INDEX-H1815.indd 362 9/15/2006 1:34:05 PM

Index

363

Binocularityreading performance, 227–228refraction routine, 124–125telescope viewing, 250, 255vision tests, 125

Bioptic telescopes, 158, 253autofocus, 254

Bitemporal hemianopia, 4Blind pension, 305Blind Persons Act (1920), 3Blind Person’s Income Tax Allowance,

302Blindness

age-related macular degeneration, 78bereavement, 105–107

acceptance, 107anger, 106denial, 105depression, 106grief, 106

cerebral, 33, 36, 37, 39chronic open angle glaucoma, 90congenital cataracts, 34cytomegalovirus retinitis, 73defi nitions, 2, 3–4, 6–7epidemiology, global, 14–15epidemiology, UK

children, 21elderly populations, 20–21population-based data, 20registration data, 17–20

pathological myopia, 66posterior uveitis, 69proliferative diabetic retinopathy,

58public perceptions, 104–105registration, 3–4, 17–20, 303

allowances, 303–304benefi ts, 304concessions, 304

social welfare services, 292Blinking, 315Blue Badge disabled parking scheme,

304Blue-tooth technology, 284–285BP1 registration form, 5Braille, 296, 297, 310

libraries, 348Brain damage, low vision therapy,

320–321

Bright fi eld magnifi ers, 218see also Flat-fi eld magnifi ers

Brightness acuity tester (BAT), 162Bumpons, 300Button guides, 277

C

Cambridge gratings, 141, 145Canadian National Institute for the

Blind, 6Canes, 283, 298Cardiovascular disease, 92, 93Case history recording, 108–109

elderly patients, 77–78functional vision assessment,

168–169refraction, 116–117

Case-controlled studies, 12Cataract, 87, 117

colour vision loss, 159congenital, 30, 33, 34, 50contrast sensitivity reduction, 88

assessment, 144discomfort glare, 161elderly patients, 21, 77, 87–89

with age-related macular degeneration, 89

clinical features, 88prevalence, 87–88visual assessment, 88

epidemiology, global, 14–15epidemiology, UK, 19, 21lighting requirements, 313myopia association, 67surgery, 88–89

information for patients, 309intraocular lens power, 126

visual function questionnaires (quality of life instruments), 173–174

Central retinal artery occlusion (CRAO), 97–98

clinical features, 97management, 97–98

Central retinal vein occlusion (CRVO), 92–94, 107

clinical features, 93differential diagnosis, 96iris neovascularisation, 93, 94ischaemic/non-ischaemic, 93

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Index

364

laser treatment, 93macular oedema, 94management, 94prophylactic laser photocoagulation,

93–94risk factors, 92–93

Central Retinal Vein Occlusion Study, 93–94

Cerebral blindness, 33, 36, 37, 39Cerebral palsy, 36Cerebrovascular accident

ophthalmic terms, 322rehabilitation

low vision therapy, 320multidisciplinary approach, 342,

344–345visual fi elds assessment, 154visual symptoms, 98–99

Certifi cate of Vision Impairment (CVI), 6, 303

Certifi cation, 302categories, 303see also Registration

Charles Bonnet syndrome, 82, 329, 331Chartered Institute of Building

Engineers’ Code, 123–161Cheque-writing guides, 282, 289, 300‘Chest’ magnifi ers, 211Childhood visual impairment, 27–53

accommodation, 190Braille use, 296, 297causes in developing countries,

15–16certifi cation, 5colour vision testing, 42contact lenses, 126contrast sensitivity assessment, 143educational requirements, 50, 51electronic vision enhancement

systems usage, 263electrophysiological testing, 30–33epidemiological data, global, 14,

15–16epidemiology, UK, 21genetic causes, 15large print text (relative size

magnifi cation), 192low vision aids, 50–52management in adulthood, 74ophthalmic disorders, 42–45

parental attitudes, 113psychological aspects, 51, 113reading addition prescription,

190–191retinoscopy, 119symbol acuity charts, 135symptomatic visual diffi culty, 38, 42see also Adolescents; Infants;

NeonatesChiropodists, 341, 342Chopping boards, 277Chorioretinal atrophy, 66Choroidal neovascularisation

age-related macular degeneration, 80, 81, 82, 83, 84

central retinal vein occlusion, 93, 94pathological myopia, 66punctate inner choroidopathy, 70serpiginous chorioretinitis, 71

Chronically Sick and Disabled Persons Acts, 292, 296

City University plates, 42Clinical audit, 167Clip-on mirrors, 156Clocks, 278, 310Closed-circuit television see Electronic

vision enhancement systemsCoil Hyperocular, 234, 235, 238Coil prismatic half-eye spectacles, 231,

232Coil ready-made hyperoculars, 235,

236Coin holders, 283Collagen vascular disease, 97Colour vision assessment, 158–160

children, 42tests

D15, 159Farnsworth 100 hue, 159Ishihara, 158PV16, 159

Colour vision lossacquired superimposed on

congenital disorder, 159, 160, 314

acquired/hereditary, 158, 159contrast enhancement strategies,

314–315rehabilitation advice, 160

Community-based services, 341

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Index

365

Community-based studies, 14Computer use, 74

childhood visual impairment, 51keyboard labelling, 285, 300screen confi guration/on-screen

enlargement, 51, 74, 286speech conversion, 51, 74, 286, 310written communication, 281see also Electronic vision

enhancement systemsComputer-generated contrast

sensitivity charts, 141, 144–145Computer-generated visual acuity

charts, 135–136Concessions, 304, 305Cone dystrophy, 38, 40, 42, 43, 46, 50,

159colour vision loss, 159genetic aspects, 43lighting requirements, 313

Confounding disability, 117Confounding factors, 12Confrontational visual fi elds

assessment, 155Congenital cataract, 9, 33, 34, 50

associated ophthalmic/systemic abnormalities, 34

genetic aspects, 34Congenital deafness, 45Congenital glaucoma, 33, 34, 36Congenital nystagmus, 33

low vision aids, 51Congenital (simple) optic atrophy,

35Congenital toxoplasmosis, 72Contact lens telescopes, 126Contact lens wear, 118

following cataract surgery with age-related macular degeneration, 89

prescribing options, 126Contact-lens-related microbial

keratitis, 13Contrast enhancement, 273

blue-blocking lenses, 283clocks/watches, 278daily living aids, 314–315domestic lighting, 287, 288electronic vision enhancement

systems, 266

glaucoma management, 92information/advice for patients, 310large button telephone characters,

278low vision therapy, 314–315playing cards/board games, 279tape recorder controls, 277writing paper, 281

Contrast reserves, 147, 148Contrast sensitivity, 288, 289

assessment, 140–145edge detection tests, 143–144low contrast acuity charts,

140–143practical relevance, 88, 145sinusoidal grating tests, 144–145temporal summation, 143

ocular predominance determination, 227

threshold requirements, 140Contrast sensitivity function (CSF),

140, 143Coordinator (key worker), 342Corneal grafts, 125Corneal scarring, 161Corneal topography, 120–121Cortical blindness, 74Counselling, 113, 300–301, 328Counting fi ngers (CF), 137Craftwork, 212Cross-sectional studies, 12Cross Cylinder, Jackson, 122Cups, 314CVI 2003, 6, 303Cytomegalovirus (CMV)

congenital infection, 36retinitis, 71, 73

quality of life questionnaires, 176treatment, 73

D

D15 test, 42, 159Daily living aids, 274–285

contrast enhancement, 314–315home environment, 277–279kitchen, 274–277labelling, 285, 300lighting requirements, 314medicines administration, 279–280reading, 282

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Index

366

social services responsibilities, 292travelling/mobility, 283–285writing, 280–281

Daily living skills, rehabilitation programmes, 296–300

Dark adaptation, 169Day centres, 346Delayed visual development, 36,

37–38, 39Denial, 105–106, 110, 112Dependence, 110–111, 321Depression, 311, 312, 320, 326Diabetes mellitus, 117

central retinal vein occlusion risk, 92, 93

glaucoma association, 90insulin injection aids, 279retinopathy see Diabetic retinopathy

Diabetic nurse, 341, 342Diabetic retinopathy, 7, 56–65, 125,

347clinical presentation, 56–58CSMO, 57elderly patients, 21, 92epidemiology, UK, 21, 60grading, 59hard exudates, 58laser photocoagulation, 60, 61–62

side effects, 62, 65low vision support, 62, 64maculopathy, 57, 60, 61–62, 92management, 61–63, 74

multidisciplinary approach, 341patient education, 58prevalence, 60preventive measures, 58progression, 58, 61proliferative retinopathy, 58, 60, 61registration data, 19retinal microaneurysms, 56, 57St Vincent’s Declaration targets,

64–65UK Prospective Diabetic Study, 58vitrectomy, 60–61

Dietary factors, age-related macular degeneration progression reduction, 86

Dieticians, 340, 341Digital voice recorders, 277Directory enquiries, 304

Disability, 7defi nition, 7–8model for rehabilitation

programmes, 294–295Disability glare, 161Disability Living Allowance, 304Disability Working Allowance, 304Disability-adjusted life-year (DALY),

14Disabled employment adviser, 341,

342Disabled Person’s Railcard, 304Disabled Person’s Tax Credit, 304Discomfort glare, 161Disorder, 7, 8Distance acuity

charts, 129–136see Visual acuitychildhood visual impairment, 51specifi cations, 136–137

comparative aspects, 138–139testing strategies, 145–146

Distance visionrefraction routine, 121–123task analysis, 168

Dome magnifi ers, 51see also Flat-fi eld magnifi ers

Down’s syndrome, 120Driving, 6, 8, 51

age-related macular degeneration, 92

with bioptic telescopes, 253glaucoma, 92visual fi eld loss, 156, 158

Drusen, 78, 80, 84

E

E-mail access, 297Early Treatment of Diabetic

Retinopathy Study (ETDRS), 61

Ferris LogMAR charts, 134–135Easyreader system, 99Eating, social aspects, 329Eccentric Fixation Charts, 317Eccentric vision, 310, 316–318

impact on social functioning, 327, 328Edge detection tests, 143–144Education, 50, 51, 347

advisory services, 341, 342

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Index

367

electronic vision enhancement systems usage, 263, 268

task analysis, 169Elderly patients, 77–100

case history recording, 77–78current spectacle use, 117–118lighting requirements, 313

home safety issues, 314for reading, 123

low vision management, 99physiological changes, 78, 79rehabilitation failure, 114vision-specifi c quality of life

instruments, 175visual assessment, 77–78visual loss-related social

impairment, 328see also Age-related visual

impairmentElectronic mobility aids, 284Electronic text conversion, 286Electronic vision enhancement

systems, 74, 192, 194, 257–268, 285–286

advantages/disadvantages, 258, 260children, 51classifi cation, 257comparative aspects, 262–263contrast maximisation, 266contrast reversal, 258, 266costs, 263, 268defi nition, 257elderly patients, 99enlargement, 192, 258, 264, 265, 268fi eld of view, 264–265head-mounted devices, 261–262image enhancement, 267‘mouse’-style devices, 258–261practical issues, 268reading, 262–263, 297

contrast sensitivity infl uence, 266

duration, 266speed, 264

self-focusing, 258training, 267–268user characteristics, 263uses, 263variable magnifi cation, 258

Electro-oculography (EOG), 30

Electrophysiological testing, neonates/children, 30–33, 39–40

Electroretinography, 30Emotional impact of visual loss,

300–301information/advice for patients,

311–312Empathy, 109, 122, 302, 318Employment, 111–112, 347

task analysis, 169use of electronic vision

enhancement systems, 263, 268

Enlarged characters, 273Enlargement, 184

electronic vision enhancement systems, 264, 265, 268

see also Image enlargement; Magnifi cation

Enlargement ratio, 184hand magnifi ers, 205spectacle magnifi ers, 226

Entopic images, 329, 331Epidemiology, 1, 10–22

bias in registration data, 7global data, 14–16

Africa, 13, 14, 15Asia, 14, 15Australia, 14China, 14developing countries, 14Europe, 14India, 14Japan, 14Latin America, 14Middle East, 14New Zealand, 14USA, 14

incidence rates, 12–13methodology, 10, 12–14UK, 16–22

age-related visual impairment, 20–21

children, 21data sources, 16government survey data, 21–22population-based data, 20–21registration data, 17–20

Epiphora/watery eye, congenital glaucoma, 34, 36

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Index

368

Equivalent viewing distance, 184, 194hand magnifi ers, 205

Equivalent viewing power, 184, 193, 194, 196

hand magnifi ers, 199–200specifi cations, 198

Erythrocyte sedimentation rate (ESR), 95

Eschenbach spectacle-mounted reading aids, 233

Experimental studies, 12Eye movements

infant/childhood visual impairment, 29

low vision therapy, 315–316social function, 329

Eye-drop dispensers, 280

F

Face recognition, 142Family and friend support, 113Family Resource Survey data, 22Farnsworth 100 hue test, 159Ferris LogMAR charts, 134–135Fetal alcohol syndrome, 36Field of view, 184

bar magnifi ers, 221electronic vision enhancement

systems, 264–265fl at-fi eld magnifi ers, 221hand magnifi ers, 207stand magnifi ers, 210, 217–218telescopes, 241, 251–252, 254, 255

Filter lenses, glare management, 162Fixation, newborn infant visual

function assessment, 28Flat-fi eld magnifi ers, 51, 218–222

advantages/disadvantages, 219enlargement calculation, 219, 221fi eld of view, 221patient instruction, 222

‘Flecked’ retina, 43, 44Fluorescein angiography

age-related macular degeneration, 82–83, 86

retinal microaneurysms (diabetic retinopathy), 57

Fluorescent lighting, 313Food slicers, 276Forster–Fuchs’ spot, 66

Foveal development, 28Framingham Eye Study, 87Franklin split bifocals, 233

apheric hyperocular lenses, 234Fresnel prisms, 156Front vertex power, hand magnifi ers,

199Functional classifi cation of disability,

11Functional vision assessment, 167–180

case history recording, 168–169task analysis, 167, 168–169

Functional visual loss, 325–337Fundus albipunctatus, 44Fundus fl avimaculatus, 40, 42, 43, 44,

46Fusion, normal development, 29–30

G

Galilean telescopes, 242contact lens/spectacle lens

combination, 254enlargement, 245exit pupil, 250, 251fi eld of view, 252length, 244, 246, 247, 248optics, 243viewing non-distant objects, 248,

249Garden cane tops, 279General medical practitioners, 340, 344General positioning satellites, 284Genetic factors

age-related macular degeneration, 78, 83–84

Best’s disease (vitelliform dystrophy), 43

childhood visual impairment, 15chronic open angle glaucoma, 90cone dystrophy, 43congenital cataract, 34Leber’s amaurosis, 36–37, 46optic atrophy, 33–34, 39, 42retinal dystrophies, 52–53retinitis pigmentosa, 47Sorsby’s macular dystrophy, 52–53X-linked retinoschisis, 43

Geneticists, 339, 340Geniculate ganglia, normal

development, 28

INDEX-H1815.indd 368 9/15/2006 1:34:06 PM

Index

369

Geriatricians, 341, 342Glare

disability, 161discomfort, 161management, 162, 283refl ective, 161sensitivity testing, 161–162

brightness acuity tester, 162Miller–Nadler, 162Vistech MCI 8000, 162

task analysis, 169veiling, 161

Glaucoma, 90, 107acute angle closure (AACG), 91adult-onset, 90central retinal vein occlusion

association, 92, 93chronic open angle (COAG), 90colour vision loss, 160congenital, 33, 34, 36contrast sensitivity reduction, 145,

333elderly patients, 90–92epidemiology, UK, 21genetic aspects, 90juvenile-onset, 90myopia association, 67normal tension, 91pigment dispersion syndrome, 90primary infantile, 90quality of life questionnaires, 176registration data, 19screening, 90visual fi eld loss, 333visual fi elds assessment, 154visual prognosis, 92

Glaucomenfl ecken, 91Goldmann bowl perimetry, 155Grief response, 106

see also Bereavement responseGroup dynamics, 320Group work, 319–320

social function discussion, 327, 329

Guide cane, 298Guide dogs, 284, 299, 347

handling/care training programme, 299

Guide Dogs for the Blind Associations, 348

Guiding techniques, 299Gyrate atrophy, 41

H

Halberg trial clip, 121, 216Hallucinatory images, 329, 331

age-related macular degeneration, 82Hand magnifi ers, 74, 198–209

advantages/disadvantages, 198, 200dioptric equivalent power, 198

calculation, 202elderly patient use, 99eye–lens distance, 207, 208

Badal optical system, 203equal to magnifi er focal length,

202fi eld of view, 203greater than magnifi er focal

length, 206less than magnifi er focal length,

205–206retinal image size, 203

fi eld of view, 207lighting requirements, 287patient instruction, 208–209patient posture, 313practical optics, 199–201relative distance enlargement, 186,

188use with spectacles, 198, 199–200,

202, 205, 209by emmetrope/corrected

ametrope, 203–205equivalent power calculation, 205magnifi er in contact with reading

addition, 205–206use when accommodating, 198, 199–

200, 202Hand movements (HM) vision, 137Handicap, 291

defi nition, 7–8Head-mounted systems

electronic vision enhancement, 261–262

luminance enhancement, 267Hearing loss, 114

in childhood, 36Refsum’s disease, 49Usher’s syndrome, 45

Hearing utilisation, 310

INDEX-H1815.indd 369 9/15/2006 1:34:06 PM

Index

370

Hemianopic fi eld loss, 154, 322, 333bitemporal, 4homonymous, 4, 98, 321low vision therapy, 321

clip-on mirrors, 156Fresnel prisms, 156

Hereditary optic atrophy, 33–34clinical features, 35

HI MAG-LVA 9, 236Hidden agendas, 111Hiding Heidi cards, 143High refractive error

infant/neonate, 33see also Myopia, high

HIV infection, 71, 73Hobbies, 263Homonymous hemianopia, 4, 98, 321Hospital consultations, 343Housing Benefi t, 304Humphreys visual fi elds assessment,

155Hypercholesterolaemia, 58Hypermetropia, compensation in

telescope viewing, 246–247Hypertension, 58, 90, 92, 93Hypoplasia, 33

I

Image enhancement, 267Image enlargement, 184, 185

calculation using equivalent viewing power, 193

methods, 185quantifi cation, 194–196relative distance, 185–189relative size, 191–192

Immunocompromised patients, 71Impairment

defi nitions/classifi cation, 7–10impact on quality of life, 169

Implantable Miniature Telescope (IMT), 89, 127

Incapacity Benefi t, 304Incidence rates, 12–13Income support, 304Income tax allowance, 303Indocyanine green angiography,

82–83Infantile (juvenile) optic atrophy, 35Infants

visual function assessment, 28–30electrophysiological testing,

30–33visual impairment

with apparent visual problem, 33–36

with multiple handicaps, 36signs, 29without detectable opthalmic

abnormalities, 36–38Infl ammatory retinopathies, 69–71

fundal changes, 72Information/advice for patients, 309

causes of visual loss, 309contrast enhancement, 310emotional impact of visual loss,

311–312hospital consultations, 343lighting optimisation, 310low vision aids, 310residual vision use, 309–310sugical interventions, 309vision substitution, 310–311visual physiology, 309

Insulin injection aids, 279International Classifi cation of

Functioning, Disability and Health (ICIDH-2), 8, 10, 11

International Classifi cation of Impairment, Disability and Handicap (ICIDH), 8

International Statistical Classifi cation of Diseases and Related Health Problems (ICD-10), 3

Interviewing patientscase history, 108–109task analysis, 108, 109–111

Intraocular hypertension, 90Intraocular lens

power, 126telescope systems, 126, 254

Introductions, 328Invalid Care Allowance, 304Inverse square law, 287, 313Ishihara test, 158

J

Jaeger charts, 149Job Seeker’s Allowance, 304Jumbo D15 test, 159

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371

Juvenile (infantile) optic atrophy, 35Juvenile-onset glaucoma, 90

K

Kay picture cards, 135Keeler A series charts, 124, 132

near (reading) charts, 149, 150, 152notation, 138–139

Keeler aspheric spectacle magnifi ers, 235–239

Keeler LVA 12, 233Keeler Redi-fi t, 237

magnifi cation, 238optical parameters, 239testing set, 237–238

Keratoconus, 120, 123contact lenses, 126

Keratometry, 120Key worker (coordinator), 342Kitchens

appliance labelling, 285, 300equipment, 274–277

Knives, 277Kollner’s law, 160

L

Labelling aids, 285, 300Labo Clip-ons, 233Lacquer cracks, 66Landolt C Acuity Test Chart Panel,

122Large button telephones, 278Large print, 191, 273

clocks/watches, 278playing cards/board games, 279tape recorder controls, 277

Laser cane, 298Laser iridotomy, 91Laser photocoagulation

age-related macular degeneration, 83, 84

central retinal vein occlusion, 93diabetic retinopathy, 60, 61–62pathological myopia, 66–67punctate inner choroidopathy, 71side effects, 62, 65

Laser trabeculoplasty, 90Lea Test system, 135, 143Learning disability, 36, 320

keratometry, 120

low vision therapy, 321retinoscopy, 119visual acuity assessment, 135

contrast sensitivity, 143Lebensohn’s rule, 125Leber’s amaurosis, 33, 36, 39

gene therapy, 53genetic aspects, 36–37, 46

Leber’s optic neuropathy, 35, 46Letter recognition software, 286Letter of Vision Impairment, 6, 303Leucocoria (white refl ex), 34

infant/childhood visual impairment, 29, 30

Life Satisfaction Index (LSIA 20, LSIA 13, LSIW 8), 173

Lighthouse Low Vision Examination Intake History Form, 168

Lighting, 273, 287–288, 289customisation, 313–314fl uorescent, 313home safety issues, 314information/advice for patients, 310inverse square law, 287, 313magnifi er use, 287reading requirements, 123reading speed infl uence, 148, 149task : surround illumination ratio,

161working distance problems, 125

Liquid level indicators, 273, 274, 276, 310

Local societies, 347–348LogMAR acuity values, 132, 133, 134

near acuity, 146notation, 137, 138–139

LogMAR charts, 141Long cane see Mobility caneLongitudinal studies, 12Low birthweight, retinopathy of

prematurity, 33Low contrast acuity charts, 140–143

see visual acuity chartsLow vision

additional disabilities/disorders, 21defi nitions, 2, 3, 10epidemiology, global, 14patients’ experience, 332–338UK elderly populations, 20–21see also Visual impairment

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372

Low vision aidsage-related macular degeneration,

80, 86children , 50–52currently used device assessment,

118eccentric vision utilisation, 318elderly patients, 99electronic vision enhancement

systems, 257–272for peripheral fi eld loss, 254–255glaucoma, 92hand magnifi ers, 198–209information/advice for patients, 310insulin injection, 279learning process, 113low vision therapy, 319magnifi cation, 183non-optical, 273–290performance evaluation, 167

quality of life instruments, 173reading speed enhancement, 148,

153–154rejection, 112–113spectacle magnifi ers, 223–240stand magnifi ers, 210–222training in use, 310working age persons, 74–75

Low vision enhancement system, 261Low vision image system, 261Low Vision Leafl et, 303Low vision quality of life instruments,

176–178Low Vision Quality of Life

Questionnaire (LVQOL), 177–178

Low vision therapy, 308–323advice for patients see Information/

advice for patientsaims, 308, 309–312

visual habits redevelopment, 312blinking, 315brain-damaged patients, 320–321colour contrast enhancement, 310,

314–315eccentric vision, 316–318eye movements, 315–316family involvement, 321group work, 319–320lighting customisation, 310, 313–314

multidisciplinary rehabilitation, 341, 346

optical low vision aids, 319posture, 313practical aspects, 312–321relaxation techniques, 313

Lowe’s Visual Function Questionnaire, 173

LVI 2003, 6, 303

M

Macular colobomata, 33Macular photostress recovery test,

57Magnifi cation, 183–196

accommodation, 190–191, 224angular enlargement, 192–193electronic (transverse) enlargement,

192, 194equivalent viewing distance, 194equivalent viewing power, 193hand magnifi er specifi cations, 198relative distance enlargement,

185–189relative size enlargement, 191–192terminology, 184–185trade magnifi cation, 184, 205

Magnifi cation ratio, 124Magnifi ers, 103, 111, 112, 114, 118, 297

enlargement quantifi cation, 194–196hand, 198–209spectacle, 223–240stand, 210–222telescope, 241–256

Measles (Rubella), 15Medicines administration, 279–280Melbourne edge test, 141, 143Metabolic physicians, 340, 341, 342Metamorphopsia, 82, 155Michelson’s function, 143Microperimeters, 156Micropsia, 82Miller–Nadler glare tester, 162Minimal angle of resolution (MAR),

137, 138–139MN read charts, 149, 152–153Mobility

aids, 283–285, 297concessions, 304rehabilitation programme, 297–298

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373

Mobility (long) cane, 283, 298training, 298–299

Mobility training, 297guiding techniques, 299long cane use, 298–299orientation skills, 299

Monocular vision, 333Monoculars, 74Motivation, 103, 111–112, 113‘Mouse’-style electronic vision

enhancement systems, 258–261Mr Happy Faces cards, 143Multidisciplinary rehabilitation, 293,

295, 340–350community-based services, 342coordination, 343, 345model services, 341–342needs assessment, 345–346patient expectations, 343, 344–345professional in-service training,

345records, 343referrals, 342–343, 344, 345–346voluntary sector, 346–349

Multifocal placoid pigment epitheliopathy, acute, 71, 72

Multiple sclerosis, 7, 117acute optic neuritis, 68–69

Myopiaassociated ophthalmic conditions,

67glaucoma, 90

compensation in telescope viewing, 246

high, 65, 67contact lenses, 126high-powered near additions, 231

pathological, 65–67choroidal neovascular

membranes, 66fundal changes, 66laser photocoagulation, 66–67

progressive, 74Myopic conus, 66myReader, 267

N

N point system charts, 149–150National Assistance Act (1948), 3, 292,

305

National Association for the Education, Training and Support of Blind and Partially Sighted People (OPSIS), 348–349

National Association of Local Societies for Visually Impaired People (NALSVI), 348

National Cataract Surgery Survey, 88–89

National Council for the Blind of Ireland (NCIB), 348

National Eye Institute Visual Function Questionnaire (NEI-NFQ), 175

National Health Servicesight tests, 304voucher system, 234

National organisations, 348–349Near acuity

add requirement prediction, 124assessment, 146–154

acuity charts, 149–150comparative acuity values, 151reading performance, 146–147

refraction routine, 123–124Near retinoscopy, 119Near vision

task analysis, 168–169testing strategies, 153–154

Needle-threaders, 277, 300Needs assessment

multidisciplinary rehabilitation, 345–346

objectives ranking, 169Neglect, 110–111Neonates

electrophysiological testing, 30–33growth of globe, 27–28normal refractive state, 27visual function assessment, 28visual impairment

with apparent visual problem, 27, 33–36

with multiple handicaps, 36signs, 29without detectable opthalmic

abnormalities, 36–38Neural pathways development, 28Nidek MP1, 156

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374

Night blindness, 38, 47, 49, 50, 52, 267, 313

electronic image enhancement, 267laser photocoagulation side effect, 62

No perception of light (NPL), 137NoIR sun shields, 162Non-optical aids, 273–289

classifi cation, 273daily living see Daily living aidsdefi nition, 273electronic, 285–286patient access, 288practical issues, 288–289

Non-verbal communication diffi culties, 327

Normal tension glaucoma, 91Nottingham Health Profi le (NHP), 172Novo Bino/Mono spectacle

magnifi ers, 233Nursing care costs, 304Nyctalopia, 44, 49, 65Nystagmus, 29, 33, 74

infant/childhood visual impairment, 30

retinoscopy, 119

O

Observational studies, 12Occlusion, reading performance

improvement, 227–228Occlusive tape, 228Occupational therapists, 340, 341, 342,

346Ocular predominance determination,

227Oestrogen therapy, postmenopausal, 93Offi ce of Population Censuses and

Surveys (OPCS) Disability Survey, 22

Onchocerciasis, 14Ophthalmic nurse, 341Ophthalmologists, 340, 341, 342, 344OPSIS (National Association for the

Education, Training and Support of Blind and Partially Sighted People), 348–349

Optic atrophy, 33, 36, 38, 39, 42genetic aspects, 39, 42heredofamilial, 33–34, 35UK registration data, 19

Optic atrophy with diabetes +/− deafness, 35

Optic hypoplasia, 33, 36, 37, 39Optic nerve development, 28Optic neuritis, acute, 67–69

clinical features, 67management, 68quality of life questionnaires,

176Optic Neuritis Treatment Trial

(ONTT), 68Optical character recognition, 297Optokinetic nystagmus, 29, 30Optometrists, 340, 341, 342, 344Orientation skills training, 299Orthoptists, 341, 342

P

Pain on ocular movement, 67Paperweight magnifi ers, 218

see Flat-fi eld magnifi ers Papillaedema, 47, 96

Parkinson’s disease, 99, 117Partial sight

defi nitions, 2, 4–5, 7epidemiology, UK, 20registration, 4–5, 303

benefi ts, 304, 305children, 21concessions, 304, 305registration data, 17–20

Partially Sighted Society (PSS), 348Patient expectations, 343, 344–345Patient–practitioner relationship, 108,

116rapport, 104, 109

Pattern dystrophy, 40Peer support groups, 294Pelli–Robson low contrast letter

charts, 141, 142Pens, 281, 282Pepper visual skills for reading test

(VSRT), 149, 152Perception of light (PL), 137Peripheral viewing techniques, 156

see also Eccentric visionPersonal care, 279–280Phacoemulsifi cation cataract surgery,

88Phakic children, 51

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375

Phantom images, 329, 331Philadelphia Geriatric Centre Morale

Scale, 173Photodynamic therapy

age-related macular degeneration, 86

information for patients, 309punctate inner choroidopathy, 71

Photophobia, 38, 161laser photocoagulation side effect, 62see also Glare

Physiotherapists, 341, 342, 346Pill organisers, 280Plate surrounds, 277Plates, 314, 329PNAC (practical near acuity chart),

153Population-based data, 20–21Portable low vision aids, 74Postage concessions, 304Posterior uveitis, 69–71

infective/non-infective, 69Posture, 313Preclinical interviews, 168Prescribing

see Low Vision aid sectioncontact lenses, 126spectacles, 125

Presumed ocular histoplasmosis syndrome, 70

Preterm infants, retinopathy of prematurity, 33

Prevalence, 12, 13UK registration data, 17

Primary hyperplastic vitreous, 33Primary infantile glaucoma, 90Prismatic Bino Comfort, 233Prismatic half-eye spectacles, 231,

232Pseudoisochromatic plate tests, 159Psychological aspects, 103–115

carers’/companions’ role, 113childhood visual impairment, 51,

113functional visual loss, 325–326patient–practitioner relationship,

108rehabilitation failure, 114response to loss of vision, 105–108

acceptance, 107–108

anger, 106denial, 105–106depression, 106–107grief, 106

Psychologists, 341, 342, 346Punctate inner choroidopathy, 70, 72Pupillary refl exes, infant/childhood

visual impairment, 29, 37Pushbikes, 51–52PV16 test, 159

Q

Quality assurance, 167Quality of life, 169–170

measurement instruments, 169–170administration, 178generic, 170–173low vision-specifi c, 176–178proxy-based, 172vision-specifi c, 173–175

terminology, 170

R

Radiation therapy, 86Radical retinoscopy, 118Rain alerts, 277Randomised controlled trials, 12Reactive depression, 106–107Reading

accommodative demand, 190–191acuity reserve

maximisation, 148requirements, 147, 196

binocular performance, 227–228with stand magnifi ers, 215, 216

contrast reservemaximisation, 148requirement, 147

contrast threshold requirements, 140

daily living aids, 282electronic vision enhancement

systems, 262–263, 264contrast maximisation, 266duration of use, 266image enhancement, 267training, 267–268

Eschenbach spectacle-mounted aids, 233

hand magnifi er use, 209

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376

image enlargement requirements, 196

lighting requirements, 123, 287near acuity determination, 123–124occlusion, 227–228performance assessment, 146–149rehabilitation programme, 296–297speed, 146, 147, 264, 296

target/letter size infl uence, 148, 149

spot or survival, 196stroke patients, 321task analysis, 109–110visual function relationship,

146–147Reading acuity assessment see Near

acuity, assessmentRecord-keeping, visual acuity

assessment, 137Recreation, 348Red desaturation, 69Redi-fi t see Keeler Redi-fi tReferral of Vision Impaired Person, 6,

303Referrals, intradisciplinary/

interdisciplinary, 342–343professional responsibilities, 345

Refl ective bands, 283Refl ective glare, 161Refraction, 116–127

case history, 116current optical corrections, 117–118history-taking, 116–117prescribing options, 125–126subjective routine, 121–125

binocularity, 124–125distance vision, 121–123lighting adequacy, 123near acuity, 123–124near additions, 123, 124optimal working distance, 121,

123pinhole acuity check, 122–123terminology, 121

Refractive errorchildhood visual impairment, 28compensation in telescope viewing,

246–247elderly patients, 99

Refractive surgery, 126Refractor head (phoropter), 121

Refsum’s disease, 49–50Regan low contrast letter charts,

141–142Regional Burden of Blindness (RBB),

13Registration, 3–7, 74, 302, 303

allowances, 303–304, 305anomalies, 7data analysis, 17–20forms, BD8, etc, 5–6, 303statutory defi nitions

blindness, 3–4partial sight, 4–5

Rehabilitation programmes, 293–295communication, 296–297content, 296counselling, 300–301daily living skills, 299–300emotional problems, 300–301failure, 114group work, 293–294mobility, 297–298practical issues, 296–300practitioner stress, 300–301setting, 293vision enhancement, 295vision substitution, 295

Rehabilitation services, 291–305aims/scope, 292, 294delivery systems, 292early referral benefi ts, 295multidisciplinary approach, 293,

295, 339–349patient access, 303

Rehabilitation workers, 340, 341, 342, 345, 346

Rejection of low vision aids/advice, 112–113

Relative distance enlargement, 185–189

required near enlargement calculation, 188, 189

spectacle magnifi ers, 224, 226Relative size magnifi cation, 191–192Relaxation techniques, 313, 331Residential care costs, 304Residual vision, 10, 309, 310Retinal detachment, 333

cytomegalovirus retinitis, 73diabetic retinopathy, 58myopia, 67

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377

Retinal development, 28Retinal dystrophies, 348

molecular genetics, 52–53Retinal pigment epithelium

detachment, 82Retinitis pigmentosa, 9, 105–106, 107,

340, 348associated neurological disorders,

49clinical features, 47, 48, 49early onset (childhood), 38, 41, 42,

45, 46, 47–49genetic aspects, 47low vision aids, 51night blindness, 38, 47, 267quality of life questionnaires, 176treatment approaches, 53Usher’s syndrome, 45visual fi elds assessment, 155

Retinitis punctata, 44Retinoblastoma, 30, 33, 34Retinopathy of prematurity, 33Retinoscopy, 118–119

children, 119cycloplegic refraction, 119near, 119radical, 118

Reverse telescopes, 156Rheumatoid arthritis, 117Room temperature, 277Rosser Index of Disability and

Distress, 173Royal National Institute for the Blind

(RNIB), 348Rubella, 15, 36, 113RVI 2003, 6, 303

S

Saccadic movement exercises, 315Saccadomania (‘dancing eyes’), 30Safety modifi cations, 273

kitchen equipment, 274–277St Vincent’s Declaration, 64–65Scanning laser ophthalmoscope, 155Scanning techniques, 156Screen-readers, 297Self-esteem, 326, 328Sensorial aids, 273–289

classifi cation, 273daily living see Daily living aidsdefi nition, 273

electronic, 285–286patient access, 288practical issues, 288–289

Serpiginous chorioretinitis, 71, 72Severe Disablement Allowance, 304Sheridan–Gardner letter matching

cards, 135Shopping, 327Short Form 36 (SF36), 172–173Sickness Impact Profi le (SIP), 172Sight enhancement aids, 300Sight substitution, 300‘Sighted guide’ skills, 293Sinusoidal grating tests, 144–145Sloan distance acuity charts, 132Sloan M series charts, 124, 149, 152Smell sensation ultilisation, 311Snellen acuity charts, 129–131Snellen equivalent (near) system

charts, 149Snellen fraction notation, 136–137,

138–139Social clubs, 347–348Social functioning, 326

eating, 329visual behaviour, 315, 328–329

Social Security Act (1935; USA), 6Social security benefi ts, 304, 305, 341Social services referrals, 342Social welfare services, 292Social workers, 340, 341, 345, 346Software, 286

speech conversion, 51, 74, 286, 310SOLA LVA 25, 233Sonic mobility aids, 284Sorsby’s macular dystrophy, 52–53Southampton Self Esteem Scale, 173Spectacle addition

use with fi xed focus stand magnifi ers, 212

optimisation, 215–216vergence of light, 214–215

use with hand magnifi ers, 198, 199–200, 202, 205–206, 209

Spectacle magnifi ers, 74, 223–240advantages/disadvantages, 223, 224aspheric, 234–239

Coil Hyperocular, 234, 235, 238Coil ready-made hyperoculars,

235, 236Keeler systems, 235–239

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378

binocular enlargement, 228–231decentration calculation, 228–230

childhood visual impairment, 51comparison with near telescopes, 239demonstration to patient, 240dioptric equivalent power, 228elderly patients, 99front vertex power, 223occlusion of poorer eye, 227–228practical optics, 223–225practical use, 240predicted add requirement, 124prism base-in incorporation, 125,

228, 229, 230prismatic half-eye spectacles, 231relative distance enlargement, 188,

224, 226shallow/half-eye frames, 226spherical, 231, 233–234

high-powered addition bifocal, 233–234

high-powered addition of single vision, 231, 233

working distance reduction, 223, 224, 225–226

Spectacle microscope, 223Spectacle presciption change, 122, 123Spectacles

current prescription, 117prescribing options, 125

Speech conversion software, 51, 74, 286, 310

Speech therapists, 341, 342Speed-reading, 296Spherical spectacle magnifi ers, 231,

233–234high-powered addition bifocal,

233–234high-powered addition of single

vision, 231, 233spot reading, 147

Stairs, 315Stand magnifi ers, 210–222

advantages/disadvantages, 210–211‘chest’ design, 211childhood visual impairment, 51elderly patients, 99fi eld of view, 210, 217–218fi xed focus, 211, 212–213fl exible ‘arm’, 211

lighting requirements, 287patient instruction, 222patient posture, 313practical optics, 211–213relative distance enlargement, 186,

188variable focus, 211–212vergence of light, 213–217

emergent vergence measurement, 216–217

reading addition optimisation, 215–216

working distance, 210Stargardt’s disease, 28, 40, 42, 43, 46,

50STEDI-FIT 10c, 236Stigma, 105, 112Storage container labelling, 285Stroke see Cerebrovascular accidentSubnormal vision, defi nitions, 2, 10Suicide, 107Sunvisors/hats, 283Support groups, 294Suppression, 227Survey data, 21–22Survival reading, 147Swedish ‘multi-lens’ concept, 234Swollen optic disc, differential

diagnosis, 96Symbol cane, 283, 298Symbol matching charts, 135

contrast sensitivity assessment, 143Syphilis, 97Syringes, 279

T

Tactile aidsclocks/watches, 273, 278, 310labelling, 285measuring tapes, 300playing cards/board games, 279scales, 273

Tactile senses utilisation, 310–311Talking aids

books (audiobooks), 277, 278, 310, 348clocks/watches, 278microwave cookers, 277, 310newspapers, 310, 347scales, 277signs, 277

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379

Tangent screen perimetry, 155Tape recorders, 277Task : surround illumination ratio, 161Task analysis, 108, 109–111

functional vision assessment, 167, 168–169

needs objectives ranking, 169preclinical interviews, 168spectacles prescription, 125

Tax relief, 304Teachers, 340, 341Telemicroscopes, 249, 255

enlargement measurement, 253Telephone button labelling, 285Telescopes, 99, 241–255

advantages/disadvantages, 241astronomical see astronomical

(Keplerian) telescopesautofocus, 254bioptic, 158, 253contact lens/spectacle lens

combination, 126, 254depth of fi eld, 246designs for mobility, 253–254enlargement, 244–245, 249

measurement, 252–253exit pupil, 250–251, 252fi eld of view, 241, 251–252, 254, 255Galilean see Galilean telescopeslength, 243–244, 246, 247, 248monoculars, 74practical aspects, 255practical optics, 241–243reading cap addition, 249, 250refractive error compensation,

246–247spectacle magnifi er comparisons,

239vergence of light, 245–246viewing non-distant objects,

248–250Television licence fees, 304Television watching, 263Temporal arteritis, 94–95, 97, 98

clinical features, 94–95corticosteroid treatment, 95differential diagnosis, 96ESR, 95temporal artery biopsy, 95visual prognosis, 95

Terminology, 1–4Text conversion, 286Text enlargement, 286Thomson Test Chart 2000, 136Timers, 276Tinted glasses, 283Touch typing, 281, 282Toxoplasma retinochoroiditis, 69–70

congenital, 36lesion reactivation, 69, 70

fundal changes, 72primary acquired infection, 70

Trabecular meshwork inducible glucocorticoid responsive gene product (TIGR), 90

Trachoma, 14Tracing exercises, 315Tracking exercises, 315, 316Trade magnifi cation, 184–185

hand magnifi ers, 205Training

electronic vision enhancement systems, 267–268

low vision aids use, 310mobility (long) cane, 283, 298–299

Traumatic visual loss, 73–74with brain damage, 320

Travel concessions, 304Travelling aids, 283–285Tray liners/holders, 277Trial frame, 121Twin studies, 84Typing

electronic vision enhancement systems use, 263

touch, 281, 282Typoscopes, 282

U

United Kingdom Prospective Diabetic Study, 58

Usher’s syndrome, 45Uveitis

anterior, 72posterior, 69

V

Value added tax exemption, 274VEGF, 86Veiling glare, 161

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380

Vibrating watches, 273Vision substitution advice, 310–311Vision-specifi c quality of life

instruments, 173–175low vision, 176–178

Visolett magnifi ers, 218see Flat-fi eld magnifi ers

Vistech MCI 8000, 162Vistech VCTS chart, 141, 145Visual Activities Questionnaire

(VAQ), 175Visual acuity, 129

normal development, 28ratings, 137, 138–139reserve requirement for reading,

147, 148Visual acuity assessment, 129–145

distance acuity charts, 129–136Bailey–Lovie, 132–133computer-generated, 135Ferris, 134Keeler A series, 132Sloan distance, 132Snellen, 130–131Symbol, 135Waterloo, 134

distance acuity specifi cations, 136–137

comparative aspects, 138–139distance testing strategies, 145–

146high contrast charts, 129–139see distancelow contrast charts, 140–145

Bailey–Lovie, 143edge detection, 144Pelli–Robson, 142Regan, 142Sinusoidal grating, 144–145Symbol, 143

near vision chartsBailey–Lovie, 152Jaeger, 149Keeler A, 150MN, 152N point, 149–150Pepper, 152PNAC, 153Sloan M, 152Snellen, 149

near vision testing strategies, 153–154

reading (near acuity), 146–154comparative acuity values, 151

record-keeping, 137Visual agnosia, 321, 322Visual alexia, 321, 322Visual asthenia, 321, 322Visual behaviour, 315, 328–329Visual development, 27–28Visual effi ciency ratio values, 137,

138–139Visual fi eld loss

driving safety, 156, 158low vision aids, 254–255patients’ experience, 332, 333rehabilitation advice/assistance,

156, 158statutory defi nitions of blindness, 4,

6, 7Visual fi elds assessment, 154–158

central fi elds, 155–156peripheral fi elds, 155

Visual Function after Pan-Retinal Photocoagulation (VF-PRP) survey, 174–175

Visual function assessment, 129–163cataract, 88colour vision, 158–160elderly patients, 77–78glare sensitivity, 161–162visual acuity see Visual acuity

assessmentvisual fi elds see Visual fi elds

assessmentVisual Function Index (VFI), 173Visual Functioning Index (VF14), 173,

174Visual hallucinations, 82Visual impairment

associated social impairment, 327, 328

defi nitions, 1–10, 303blind registration, 3–7Canada, 6children, 5Europe, 6–7USA, 6World Health Organisation, 2–3

elderly people, 77–100

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381

see also Age-related visual impairment

information/advice for patients, 309traumatic causes, 73–74working age persons, 56–75see also Low vision

Visual Performance Questionnaire (VPQ), 175

Visual physiologyageing-related changes, 78, 79information/advice for patients, 309

Visual Status Inventory (VSI), 175Visually directed reaching, infant

visual function assessment, 29Visually evoked potential (VEP), 30Vitelliform dystrophy (Best’s disease),

42–43, 46, 50Vitrectomy, 60–61Vitreous haemorrhage, 58Voice recorders, 273Volk lens, 57Voluntary sector, 346–349

individual volunteers, 346–347local societies, 347–348national organisations, 348–349

Voting, 304VTM dome, 219

W

Wallets, 283Watches, 273, 278, 310Waterloo charts, 134Webber function, 143White refl ex see LeucocoriaWhite sticks see Canes

Working distanceaccommodation for near vision

improvement, 190–191electronic (transverse) enlargement,

192reduction with spectacle magnifi ers,

223, 224, 225–226relative distance enlargement, 185,

186relative size magnifi cation, 192spectacles prescription, 125

World Blind Union, 7World Health Organization (WHO)

defi nitions of visual impairment, 2–3

International Classifi cation of Functioning, Disability and Health (ICIDH-2), 8, 10, 11

International Classifi cation of Impairment, Disability and Handicap (ICIDH), 8

World wide web access, 297Writing, 328

aids, 212, 280–281guides/frames, 281, 300

implements, 281, 282paper, 281rehabilitation programme, 296use of electronic vision

enhancement systems, 263

X

X-linked retinoschisis, 41, 42, 43X-linked retinitis pigmentosa, 47

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low vision manual-0750618159

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