low vision evaluation

Low Vision EvaluationLow Vision Evaluation

Ms MB JAN- 24/01/2012

ContentContent

1. The difference between a low vision exam and a regular exam

2. The Case History3. Evaluating visual performance

4. Evaluating visual performancei. Visual acuityii. Visual field evaluationiii. Contrast sensitivityiv. Colour vision5. Objective refraction6. Subjective refraction7. Ocular health evaluation

OUTCOMESOUTCOMES

At the end of this lecture, learners should be able to:

Discuss the importance of a case history specifically for a low vision patient

Discuss specific questions that will be asked to a low vision patient

Describe the different techniques and charts used to measure a low vision VA (near, distance, aided, unaided etc.)

Discuss the need for evaluating visual fields in a LV patient

Discuss methods and techniques for evaluating visual fields in a LV patient

Discuss the need for evaluating contrast sensitivity in a LV patient

Discuss the need for evaluating colour vision in a LV patient

Discuss the methods and techniques used for evaluating colour vision in a LV patient

Discuss the objective refraction techniques available to the low vision optometrist

Discuss the technique and implications of radical retinoscopy

Discuss the method used for refracting a low vision patient

Analyze a low vision case based on a history, and then decide on and describe the most appropriate evaluation routine for a specific patient

Distinguish between a low vision refraction routine and a normal refraction routine

Explain the concept of JND (just noticeable difference) and be able to use it to test a low vision patient

The pre-evaluation information The pre-evaluation information sheetsheetIt sets clear boundaries on what

you will be able to doDraw up your own sheet in

practice

Information sheetInformation sheet

1. The appointment duration2. Schedule appointment around a

time when patient’s vision is stable

3. Bring with old glasses, magnifiers – even if not usable anymore

4. Think about specific problems the patient is experiencing

5. Start thinking in terms of goals – write down what you would like to achieve

6. Bring along special materials he/she want to be able to use (E.g. books)

7. Bring along a report from the ophthalmologist

8. Follow-up visits or training sessions with equipment may be necessary

9. State that there are no miracles, we will use your remaining vision effectively

The difference between a low The difference between a low vision examination and a regular vision examination and a regular exam exam

Give the differences and explaineach point given

Disadvantages of using Disadvantages of using phoropterphoropterWhy not phoropter?

Case HistoryCase HistoryNB. Very important, It has to be even more detailed

The patient interviewThe patient interviewThe successful patient interview

has 3 functions (Cohen-Cole)◦Gathering data to learn about the

patient’s problem◦Developing rapport, and responding

to the patient’s emotions◦Educating patients about their

problems, and motivating them to adhere to the prescribed treatment

Interview techniquesInterview techniquesBoth parties should be seated at

eye-to-eye heightSeating should be comfortableControl lighting – not too dim or

brightCarefully observe the patient

Use both open-ended and specific questions

May be emotionally chargedNote taking should be done subtly

Be alert to inconsistencies Take sufficient time that patient

doesn’t feel rushed BUT keep it brief – old people tire

more easily Use positive languageQuestion in a friendly, enthusiastic

manner

Adjust pace to that of patient.Don’t use medical jargon, explain

patient’s condition if they do not understand it

Never give false reassurancesPrimary aim is to help patient – don’t

fear to be inquisitive – but respect privacy too!

The purpose of the case The purpose of the case historyhistory

Why is it important to take LVcase history?

The real questions you want The real questions you want answered are:answered are:1. What does the patient want?2. What does the patient need?3. What is the real reason for the

patient’s visit?

Information requiredInformation required1. Basic identifying information

◦ Name, address etc

2. Who accompanied the patient?◦ Support system / self-sufficient?◦ Relative, friend, counselor, teacher

etc◦ Contact person◦ Provide insight into history

3. Referral source◦ Send thank you note◦ Reports

4. Diagnosis of eye condition◦ In patient’s own words◦ See if patient understands condition◦ Begin with patient education on

problems.

Visual historya. Durationb. Previous carec. Nature of vision loss (congenital or

acquired? Stable or progressive?)d. Fluctuation of vision

e. Problems with color visionf. Is there a preferred eye?g. Problem with glare or lighting?h. Current glasses / low vision aidi. Current visual capability (specific task-

related questions)i. Smallest print read? Newsprint Headlines Large print

ii. Able to watch television? ◦ What viewing distance?◦ Size screen?iii. Can you recognize faces at a distance?iv. Can you see well enough to get

around?

l) Family visual history

5. Medical historya) Undergoing treatment for medical

condition?b) Does the patient have a disease

with known ocular implications?c) Is there medical problems that

might affect the use of a LVA? (stroke)

d) Family historye) Allergies and drug sensitivitiesf) Medications (many systemic drugs

have ocular side-effects)

6. Employment or school history◦ Investigate the effect the visual loss

has on the work/school performance◦ Investigate the use of appropriate

devices to alleviate problems◦ Some older people might want to

continue their education

7. Avocations◦ Hobbies or activities

8. Social assessment◦ Does the patient live alone or with

family?◦ How is daily life affected by the vision

problem?◦ Does the patient have a support

network?◦ Is the patient’s independence

threatened?

10. General appearance of patient◦ Well groomed, clean or untidy?◦ Food stains – cannot see that level of detail◦ Poor grooming - emotional disorders such as

depression◦ Walk without assistance?◦ Mobility ◦ Does the patient look ill?

11.Patient goals (Chief complaint) Possibly the most important part of

the case history Allow a full elaboration of the visual

disabilities Patient’s new problem should be

fully investigated

After the patient has completed a list of complaints, several issues should be addressed regardless of the patient’s failure to mention thema. Distance visionb. Near visionc. Orientation and mobility skillsd. Glaree. Lifestyle

External evaluationExternal evaluationSome do this just after VA’s, but

depends on circumstances. Give an example

Brief look into the eyes, do not shine bright lights into the eye

Note the following about the eyes:◦Position of eyes (strabismus)◦Pupil – size, reaction to light,

appearance, ◦Cornea – opacities: size, density,

position◦Lens – opacities, position (especially IOL)◦Motility – strabismus, nystagmus,

restrictionsBinocular dysfunction is usually of

secondary importance

Evaluating visual Evaluating visual performanceperformance

Why?Why?Compare with normal

performance, or accepted standard (eg driving regulations)

Set a baseline for monitoring the condition

Quantify the patient’s own subjective impression of visual performance

Early detection and diagnosis of (other) visual disorders

Assessment of the benefits of an intervention (medical, surgical, rehabilitation) program

Predicting visual function in every day tasks

Visual acuityVisual acuity

Visual acuityVisual acuity1.Why do we want to accurately

measure acuity? 2. Limitations of VA measurement3. Factors affecting VA measurements4. Distance Visual Acuity5. Near Visual Acuity

Why do we want to accurately Why do we want to accurately measure acuity? measure acuity? i. It establishes a baseline from

which to monitor pathologyii. Used to predict the magnification

level of the optical devices that will be required to achieve the patient’s goals

iii. Often requested by other agencies to establish legal blindness, driving privileges, job eligibility etc.

Limitations of VA Limitations of VA measurementmeasurementi. The clinical acuity does not

give an accurate indication of the functional acuity. Explain

ii. Clinical measure of person’s ability to read letters under controlled circumstances

iii. It doesn’t always correlate with daily activities

iv. Function can be influenced by differences in contrast sensitivity, glare sensitivity, motivation and numerous other factors

v. VA can vary due to test setting, illumination, doctor-patient relationship and target contrast

Factors affecting VA measurements

How does each of the following How does each of the following factors affect VA factors affect VA measurement?measurement?i. Lightingii. Optotypeiii. Mental state of the patientiv. Instructions to patient/attitude /

encouragementv. Glare recoveryvi. Educational levelvii. Recognition/memory/speechviii. Motivation

Distance Visual AcuityDistance Visual Acuity

a. VA Notationsb. Acuity chart designc. Currently used chartsd. Measuring distance VA

a.a. VA NotationsVA Notations

1. Snellen◦ Either metric or imperial◦ We use imperial (feet)

2. LogMar (logarithm of the minimum angle of resolution)

3. Decimal: Snellen fraction4. Angular (specified in minutes of arc)

◦ Not used clinically

b.b. Acuity chart designAcuity chart design

The following aspects of chart design can be considered

i. Optotype –◦ style of print and selection of letters◦ Should yield equivalent results to

Landolt Cii. Number of letters per row

◦ Equivalent – equal task progression◦ 5 good clinically

iii. Sequence of Letters ◦ not form words/part of words

iv. Optotype Size◦ 0.1 logarithmic progression of

character size◦ Accurate measurements at both

standard and non-standard test distance

v. Letter spacing ◦ systematic

c.c. Commonly used charts Commonly used charts

1. Feinbloom Number Chart

Refer to your notes for advantages and disadvantages

Of this chart

2. Bailey-LovieAdvantages logMar format Equal number of

letters at each line

Can be used at any test distance

3. Projected cards4. Other

1. Lighthouse distance acuity card (available in our clinic)

2. Lighthouse symbol cards3. Designs for vision pediatric picture

chart4. University of Waterloo Chart5. ETDRS chart

d.d. Measuring Visual Measuring Visual AcuityAcuity

Use special low vision chartsUse a 10feet / 3 m working

distance, or lessEmphasize residual visionOffer encouragement and

realistic feedback

Watch for and encourage eccentric viewing

Let the patient attempt to read all letters on the chart, and look for scotomas

Record as Snellen fraction, e.g 10/700 To convert between feet and meter,

divide by 3.25 (feet to meter) or multiply by 0.3 (meter to feet)

Always measure the acuity correctly: “less than 6/60” is unacceptable

Recording VA Recording VA MeasurementsMeasurementsCan have a measurement

recorded as BEO (both eyes open) – distinguish from OU

Record the fractions read:10/240 + 2 of 10/200 + 1 of 10 / 180

If the patient is unable to If the patient is unable to identify any optotypes, which identify any optotypes, which designations are you going to designations are you going to use?use?

Near VANear VAThe measurement of Near VA is a

very important part of low visionMost low vision patients struggle

with reading, so magnification for near tasks is vital.

Near VANear VA

a. Specification of Nearpoint acuityb. Measuring near acuity with the

M system

a.a. Specification of Specification of Nearpoint acuity Nearpoint acuity

i. M notation◦ Method of choice◦ Metric notation◦ Represents the distance in meters at

which the target subtends an angle of 5’ of arc

◦ 1.00M subtends 5’ at 1m◦ Consistent, meaningful, flexible testing

distance

ii. N notation◦ Point size of lower case Time Roman

print◦ Standardized so that each point is 0.18

mm on the printed page◦ N10 is twice N5◦ Quite valid◦ Necessary to specify both test distance

and target size

iii. Point type◦ Actual print size in printers point notation◦ Size of slug, but not actual print size◦ Not a very good system

iv. Reduced Snellen◦ Characters subtend the same angle indicated

by the designated fraction at 20 feet◦ Specified test distance◦ Not 20 units, not a standard angle at 20

distance units◦ Cannot be used at any other distance◦ Useless - inflexible

Visual field evaluationVisual field evaluationThis another important aspect in

low vision patientDesirable to test all patient’s

fields, but not always possible or practical

Instruments and Instruments and techniquestechniques1.Confrontation test

◦Only a gross estimate of the peripheral field

◦Screening method◦Use light as a target

2. 2. Amsler gridAmsler grid

a. What is it?◦ Hand-held chart used to evaluate central 20°

of vision◦ Can identify early changes like

metamorphopsia or small central scotoma

b. What does it look like?◦ 20 blocks x 0.5mm each

c. How does it work? “Place a finely quared chart before an eye

suffering from an affection of the central region of the retina, and the patient will immediately point out spots and distortions which affect his/her vision”

Measures the central 20° of vision if the chart is held 28-30cms from the eye

d.d. Types of chartsTypes of charts

i. Standard chart * Every case, and usually sufficient

ii. Diagonal lines* Use with central scotoma

iii. Red on black standard chart Colour scotoma

iv. Spots only Reveals scotoma (no lines to be

distorted)

v. Parallel lines Use horizontally and vertically Shows metamorphopsia

vi. Parallel lines for reading Allows a more minute evaluation of

reading area

vii. Standard block with smaller reading area

Minute examination of juxta-central area Rectangle shows limit of fovea

e.e. General methodGeneral method

Testing distanceOptimal refractionClean, clear, well-lit chartNo ophthalmoscopy etc prior to

evaluationDo monocularly and then BEO to

check for interference/suppression

What chart?◦Start with grid◦Then use lines and spots

Do monocularly and then BEO to check for interference/suppression

f.f. Questions askedQuestions askedi. Do you see the white spot in the

centre of the squared chart?ii. 4 corners? 4 sides? Whole of the

square?iii. Network intact?iv. Lines straight + parallel?v. Anything else?vi. Plotting the distortions?

Colour visionColour visionPathological conditions like

glaucoma and ARMD can cause changes in colour vision, so it is necessary to evaluate this. ◦City University (not available in our

clinic )◦Isihara ◦Farnsworth D15

IsiharaIsihara

Tests for colour deficiency of congenital origin

Limited value in LV

Farnsworth D15Farnsworth D15

Available in our clinic

Check functional tests notes

Refraction Refraction Always obtain the best possible refraction with the best possible VA – to give the lowest magnification, why?

Objective refractionObjective refraction1. Autorefractors

◦ Limited use, due to media problems or eccentric viewing (off axis fixation)

2. Previous glasses◦ Can be a good starting point◦ Just make sure patient is using own

Rx!◦ Patient might have had ocular

surgery since glasses were prescribed

3. Keratometry◦ Useful with astigmatism – amount and

orientation of cyl◦ Patient may have difficulty fixating◦ Can be helpful in detecting irregular

corneal surfaces or irregular astigmatism

4. Retinoscopy◦ Very useful, especially if patient is a

poor responder◦ May be necessary to use radical

retinoscopy

Retinoscopy ◦Always do the ret in a trial frame◦If there is no initial response or no reflex

is seen, try using very large lens changes like +/- 5D, +/- 10D, +/- 20D

Radical retinoscopyRadical retinoscopyRadical retinoscopy means that

the working distance is drastically reduced (as close as 10cm)

Radical retinoscopy can also mean deliberate off-axis scoping to use any visible reflex – this will induce unwanted cylinder, but the results can be potentially valuable

Subjective refractionSubjective refraction

1 General conditions2 The trial frame3 The JND (just noticeable

difference)4 Spherical refraction5 Cylindrical refraction

General conditionsGeneral conditionsUse a 10feet or less working

distanceUse full illumination unless

otherwise indicated (e.g. patient with achromatopsia)

Use the low vision chart in subjective refraction

Always do a trial frame refraction

The trial frameThe trial frame

Why do we use it?

The refraction itselfThe refraction itselfUse standard methods and background knowledge to refine cylinder axis, power and sphere power

The JND (just noticeable The JND (just noticeable difference) difference) Essential conceptThe smallest dioptric step that a

patient is able to discriminateIt is senseless and frustrating to

use 0.25D steps when (because of the visual impairment) the patient can only notice a 1.00D change

Use the 10-feet equivalent as a rough starting point for JND

If the best VA is 10/100, the JND will be 1.00D

10/50 = JND of 0.50D

Spherical refraction Spherical refraction Use the tentative result from your

objective refraction as a starting point

Determine the JND-lens, and check the sphere value with that

“Better with the lens, or without it”, not “one or two”

Patients may have a poor, slow, variable response – could be due to pathology

Cylindrical refractionCylindrical refractionCheck the axis using a hand-held

Jackson Cross-cylinder of +/- 0.50D or +/- 1.00D if possible

You can also use rotation to blur/clear and let the patient rotate the axis her/himself

Cylinder power is checked in the normal way

Double check cyl power with direct

comparison (with or without) – if no subjective or objective improvement, it is not necessary to prescribe

Finally, double check the spherical component again – use bracketing (eg +0.50 and -0.50 should blur equally)

Ocular health evaluationOcular health evaluation

OPTIONS:◦Ophthalmoscopy◦Keratometry◦Tonometry◦Slitlamp ◦Von Herick◦Dilated fundus exam◦Binocular indirect ophthalmoscopy