OPTOMETRIC TERMINOLOGY

“A pattern” – a horizontal deviation may be different in upgaze versus downgaze. An “A pattern” deviation shows more eso (or less exo) in upgaze.

Abduction – movement of the eyes away from the nose.

Accommodation – the act of focusing the eyes to provide an image clear enough for interpretation. The stimulus to accommodation may come from blur on the retina, or perceived awareness of the proximity of a target. Accommodation is said to be “stimulated” when looking at near objects, and “relaxed” when looking further away. Accommodation is part of the “identification” system; it tells us the “what is it?” of what we are looking at.

Accommodative amplitude – the range of distance or lens power over which the patient can stimulate focus to maintain clarity. A patient who shows a reduced amplitude is said to have an accommodative insufficiency.

Accommodative flexibility- ease with which accommodation can be changed from one distance to another. A patient who has reduced flexibility is said to have accommodative infacility.

Accommodative Spasm- difficulty releasing (relaxing) accommodation.

Acquired Brain Injury (ABI) refers to damage to the brain acquired after birth. It usually affects cognitive, physical, emotional, social or independent functioning and can result from traumatic brain injury (i.e. accidents, falls, assaults, etc.) and nontraumatic brain injury (i.e. cerebral palsy, stroke, brain tumours, infection, poisoning, hypoxia, ischemia or substance abuse). See also TBI

(Visual) Acuity (VA) – clearness or sharpness of sight, the ability to resolve or discriminate contours and to tell when there is a separation of the contour from its background. In the US, it is usually represented as a fraction, which identifies the size of the smallest letters resolved at the testing distance used. The numerator (top number) represents the testing distance used, typically 20 feet. The denominator (bottom number) has to do with the size of the letter read. For example: 20/20 means that an individual is able to resolve the letter on the 20/20 line of the Snellen chart at 20 feet.

Adduction – a movement of the eyes toward the nose.

Afterimage – a visual sensation that persists after the original light stimulation has ceased.

Alternating – switching from one eye to the other. In relation to strabismus, it means that either eye may fixate while the other eye deviates.

1

Amblyopia – the visual condition in which there is a low or reduced central visual acuity that cannot be “corrected” by traditional refractive means (eg. glasses or contact lenses), and which is not attributable to disease, injury, or pathology. Amblyopia is said to exist when there is a set level of acuity, typically 20/40 or worse, or when a difference of 2 or more Snellen acuity lines between the eyes is present. Behaviorally amblyopia is looked upon as a dysfunction that hinders a patient’s ability to gather, process, analyze, and respond to visual information in a meaningful way.

According to Ciuffreda, in functional amblyopia (amblyopia ex anopsia) usually one or more of the following conditions is present before the age of six years and accounts for the amblyopic condition: significant anisometropia, constant unilateral esotropia or exotropia, significant isometropia, significant unilateral or bilateral astigmatism, or image degradation. Binocular competition in an amblyopic patient causes adaptations to be made via neural suppression, leading to reduced VA and dysfunctions in such skills as ocular motility, fixation, accommodation, spatial sense, and speed of perception in the amblyopic eye. Vision Therapy has a high rate of success for patients with functional amblyopia to both improve visual acuity and to develop abilities in the visual functional areas (as mentioned above) that are commonly affected by this condition.

Anaglyphs – are used to provide a stereoscopic 3-D effect, when viewed with special anaglyph glasses (each lens a different color, usually red and green or red and blue). Images are made up of two color layers, superimposed, but offset with respect to each other to produce a depth effect. The picture contains two differently filtered colored images, one for each eye. When viewed through anaglyph glasses they produce a unified stereoscopic image

Analytical examination – a comprehensive optometric exam that probes the functioning of the visual system under varying conditions. The findings from this evaluation help the optometrist to understand how vision might be helping or interfering in the patient’s performance, comfort, etc.

Angle Kappa – the angle between the pupillary axis and the visual axis. It is termed “positive” when the pupillary axis is nasal to the visual axis and “negative when the pupillary axis is temporal to the visual axis. A positive angle kappa (displacement toward the nose) of up to 5 degrees is normal.

2

Aniseikonia – a condition in which the image of an object seen by one eye is different in size and shape from the image seen by the other eye. Anisometropia – the condition in which unequal refractive states exist between the eyes.

Anomalous Correspondence (AC) – in strabismus, the condition in which an area other than the fovea of the strabismic eye is “matched” with, or “corresponds” to the fovea of the other eye as far as determining location and direction. This provides the patient with some degree of “depth perception,” and avoids double vision and visual confusion.

Anterior Chamber – the space between the iris and the cornea.

Antimetropia – the condition where one eye measures hyperopia, and the other eye, myopia.

Aphasia – a loss of the ability to produce and/or comprehend language, due to injury to brain areas specialized for these functions, such as Broca's area, which governs language production, or Wernicke's area, which governs the interpretation of language. It is not a result of deficits in sensory, intellectual, or psychiatric functioning, nor due to muscle weakness or a cognitive disorder.

Apraxia – a neurological disorder characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire and the physical ability to perform the movements. It is a disorder of motor planning which may be acquired or developmental.

Aqueous Humor – the thin, watery fluid that fills the space between the cornea the iris (anterior chamber).  It is continually produced by the ciliary body, the part of the eye that lies just behind the iris. This fluid nourishes the cornea and the lens and gives the front of the eye its form and shape.

Asthenopia – a constellation of symptoms relating to visual discomfort, usually at near, such as blurry vision, watery eyes, itchy eyes, etc.

Astigmatism – the refractive condition in which the light rays from an object are not brought to a single point focus at the back of the eye. Astigmatism is compensated for by the use of lenses with cylinder.

Ataxia –a neurological sign and symptom consisting of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of parts of the nervous system that coordinate movement, such as the cerebellum, the vestibular system, the thalamus, and parietal lobe.

Autonomic nervous system (ANS) – the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These activities are generally performed without conscious control. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, micturition (urination), and sexual arousal. Whereas most of its actions

3

are involuntary, some, such as breathing, work in tandem with the conscious mind. The ANS can be divided by subsystems into the parasympathetic nervous system and sympathetic nervous system. It can also be divided functionally, into its sensory and motor systems.

Bagolini lenses – a pair of finely straited lenses that can be used in diagnosing the status of Correspondence.

Bifocal – a lens which contains two different powers for focusing at different distances. Typically, the bottom part of the lens is for looking at near distances (usually 13 to 16 inches), and the top portion of the lens is for looking further away.

Binocular – also, referred to as “fusion,” refers to the simultaneous perception of information from the right eye and the left eye, organized into a single percept. Binocularity occurs in the brain, and not at the retina. Some of the advantages of Binocular vision are: single vision, stereopsis, enlargement of the field of vision, and compensation for the physiological blind spot.Normal Binocular vision requires:

o Reasonably clear vision in both eyes

o The ability of the retino-cortical elements to function in association with each other to promote the fusion of two slightly dissimilar images i.e. sensory fusion

o The precise co-ordination of the two eyes for all directions of gaze, so that corresponding retino-cortical elements are placed in a position to deal with two images i.e. motor fusion.

Binocular Summation – also called neural summation, when some cells in the visual cortex receive input from both eyes simultaneously, they show binocular facilitation, a greater level of activity than the sum of the two activities evoked separately from each eye. (1 + 1 = 3)

Biocular – refers to the simultaneous perception of information from the right eye and the left eye.

(Physiological) Blind Spot – the place in the back of the eye where the optic nerve leaves to carry information along the visual pathways. Because there are no retinal receptors (rods and cones) in this area, and the nerve is myelinated, rays of light that fall on this part of the retina are not “seen” or transmitted along the optic nerve. We have a physiological (“normal”) blind spot in each eye. During the eye health evaluation, the optometrist probes the size and location of this blind spot, to see if it is normal, and whether there are any “blind” spots (scotomas) in places where there should not be any (“pathological”).

Blindsight – a condition in which the individual responds to visual stimuli without consciously perceiving them. The retina sends its major neural output (after a relay at the LGN in the thalamus) to the visual cortex (striate cortex). This is called the geniculostriate visual pathway. When the striate cortex is removed or

4

damaged, patients can still carry out certain visual discriminations although the level of capacity may change. This is so because there is another visual pathway (called the tectopulvinar pathway) that goes directly from the retina to the Superior Colliculus, Pulvinar, and Parietal Lobe without going to the Visual Cortex, and these structures may remain intact even when the striate cortex is damaged or removed. To see a video demonstrating blindsight, go to: www.beatricedegelder.com/books.html; once there click on TN-blindsight movie. 

Blur – lack of clarity.

Blur point - the point at which an object of regard becomes blurred with the introduction of increasing prism or lens power, or by varying the target’s distance. It may be measured either monocularly or binocularly. Binocularly it represents the point at which the individual maintains a target single by calling upon changes in accommodation.

Break point – during binocular fixation, the point at which diplopia (double vision) occurs with gradually increasing prism or lens power, or by varying the target’s distance.

Brückner Test – A diagnostic test performed using the direct Ophthalmoscope. It may help diagnose asymmetric refractive error, fundus lesions, cataract, and strabismus.

Cataract – the condition in which the crystalline lens loses its transparency and obstructs the passage of light. May be due to the normal aging process or as a result of trauma, etc.

Centering – the selection by the individual of an area of space to direct attention and derive meaning. It is part of the system that tells us the “where is it?” of objects of regard.

Central Nervous System (CNS) – consists of the brain and spinal cord, which serve as the main "processing center" for the entire nervous system, and control all the workings of the body. The CNS is responsible for receiving and interpreting signals from the peripheral nervous system and also sends out signals to it, either consciously or unconsciously.

5

Central Visual Field – the portion of the visual field, directly straight ahead of the eyes, in which we can see clearly and observe detail. This is in contrast to the peripheral field, sometimes called “side vision,” over which we have awareness, but see less distinctly.

Cerebellum – a region of the brain that plays an important role in the integration of sensory perception, coordination, and motor control. In order to coordinate motor control, there are many neural pathways linking the cerebellum with the cerebral motor cortex (which sends information to the muscles causing them to move) and the spinocerebellar tract (which provides proprioceptive feedback on the position of the body in space). The cerebellum integrates these pathways, like a train conductor, using the constant feedback on body position to fine-tune motor movements. Because of this “updating” function of the cerebellum, lesions within it are usually not so debilitating as to cause paralysis, but rather present as feedback deficits resulting in disorders in fine movement (eg. spasticity), equilibrium, posture, and motor learning.

Cheiroscope – an instrument that presents a pattern or image to one eye, which is transferred to and projected out of the other eye. It is used to probe the presence of first-degree fusion and the stability of binocular posture. The 2 primary types of cheiroscope are Wheatstone, which uses sphero-prisms, and the Mirror Stereoscope, which uses mirror images.

Ciliary muscle – the smooth muscle fibers in the area behind the iris that aid the crystalline lens in changing its shape for accommodation.

Comitant – or concomitant, in strabismus, when the angle of deviation is the same in all positions of gaze.

Concave lens – also called minus lens. A lens that is thinner in the middle and thicker at the edges. It is used to compensate for myopia, or nearsightedness. In the Vision Therapy room it is used to cause changes in accommodation and convergence, and to help develop a better balance between these two systems. Concave (minus) lenses make objects appear smaller and closer, the SI of SILO.

Cone – a light-sensitive retinal receptor found in great abundance at the fovea, or macular area. The cones are responsible for clear central vision, color perception, and bright-light seeing. Cones transform light information into chemical energy so that it can be used by the visual system.

Confusion – the condition in strabismus where each of the 2 foveas receives an image of a different object. If these images are not suppressed, and Correspondence is normal, the patient will perceive the 2 objects as superimposed and in the same location. In strabismus of long-standing, the patient is rarely aware of Confusion, due to suppression.

Conjunctiva – a mucus membrane covering the anterior surface of the eye and the lining of the lids.

6

Constant – always present. In relation to strabismus, it means that one eye is always deviated (turned) while the other eye fixates; there is never a time when the eyes are aligned. A patient with constant strabismus may alternate (switch) the eye that deviates, but typically one eye is preferred for fixation.

Contrast Sensitivity – the visual ability to see objects that may not be outlined clearly or that do not stand out from their background. The ability to see a shade of gray on a white background or to see white on a light gray background declines with age. Lack of contrast sensitivity is not the same as blurred vision. Contrast sensitivity is often referred to as "functional vision" beyond how well you see details on a standard eye chart. Low contrast sensitivity may result in problems with night driving, including inability to see traffic lights or spot other cars and pedestrians. People with poor contrast sensitivity also may require extra light to read, and their eyes may become tired when they read or watch television. Poor contrast sensitivity also can cause you to stumble when you fail to see that you need to step down from a curb onto similarly colored pavement.

Low contrast sensitivity can be a symptom of certain eye conditions or diseases such as amblyopia, cataracts, glaucoma, or diabetic retinopathy. Reduced contrast sensitivity sometimes occurs as a side effect of laser vision surgery procedures including LASIK and PRK.

Convergence – the turning inward of the lines of sight to attain or maintain single vision. In the real world there is only convergence, unless fusion is prevented by mechanical or other reasons (such as strabismus). We use the word “divergence,” but it is a relative term, meaning that the eyes are relatively less converged than they were previously.

There are 5 types of convergence:• tonic – the normal muscle tonus present in the living eye• proximal – a “psychological” component, based on perceived awareness

of the closeness of an object• accommodative – convergence reflexly related to accommodation• fusional – convergence stimulated by perceived disparity to attain or

maintain single vision; usually occurs at sub-conscious level• voluntary – the aligning the two eyes with conscious effort

The various types of convergence are controlled by centers in different areas of the brain; all the components must be integrated if fusion is to be effortless. This allows conscious effort and attention to be directed elsewhere.

Convergence Excess – more eso is measured at near than at far. Convergence Insufficiency – more exo is measured at near than at far.

Convex lens – also called plus lens. A lens that is thicker in the middle than at the edges. It is used to compensate for hyperopia, or farsightedness. In the Vision Therapy room it is used to cause changes in accommodation and

7

convergence, and to help develop a better balance between these two systems. Convex (plus) lenses make objects appear larger and further, the LO of SILO.

Cornea – a transparent avascular tissue at the front of the eye which is the first surface that light entering the eye passes through. The cornea forms a major part of the refractive, or “light bending” part of the visual system.

(Normal) Correspondence – in normal binocular vision the fovea of the right eye “corresponds to” or is in “correspondence with” the fovea of the left eye. When corresponding areas of the retinas are stimulated by images of the same or compatible objects, the patient appreciates single vision, or fusion. These retinal areas are “matched” between the eyes, and the stimulation of a pair of corresponding points gives rise to the same visual direction which the brain always localizes in the same direction, whether or not the stimulus is actually from this direction or not.

Cortical level – at the conscious level of thought.

Cover Test – a probe used by the optometrist to provide information about eye teaming. There are 2 types of cover test:

o Alternate Cover Test: a test to detect the presence of a phoria or strabismus. The patient’s attention is directed toward a small fixation target and one eye is occluded for several seconds. The cover is then quickly moved to the other eye. If the eye that had been under the cover moves upon uncovering it, either a strabismus or phoria is present.

o Unilateral Cover Test: A test to detect the presence of a manifest deviation (strabismus or tropia) in the alignment of the eyes. The patient is directed to look at a small target with both eyes and then an occluder is used to cover one eye. The doctor monitors the movement (if any) of the non-covered eye. If there is movement, the presence of a strabismus (tropia) is indicated.

Crystalline lens –the structure in the eye that changes its shape and power to achieve changes in accommodation in response to blur on the retina or a perceived change in distance of the object of regard.

Cyclopean Eye – when looking with two eyes we see the world as if from a single point. This is called cyclopean vision, and the point is called the cyclopean eye. (Cyclops was a one-eyed monster in Greek mythology.) Every perceived visual point has a single perceived visual direction from this cyclopean eye: egocentrically up-down-to the right- or to the left. Thus, binocular localization is integrated and referred to a point which represents the felt position of the body.

Cyclotropia – a type of strabismus in which the vertical axis of the eye is rotated away from the vertical position. This is often the by-product of surgical intervention (strabismus surgery).

8

Examples:

Cylinder – a type of lens which does not have uniform power throughout. There is full power in one meridian of the lens, gradually decreasing in power to “zero” at a point 90 degrees away from the meridian of power. Cylindrical lenses are used to compensate for astigmatism.

Depression – aiming the eyes downward.

Diopter – a unit of measurement to designate the refractive or bending power of a lens or optical system. The term “diopter” is used in expressing measurement of both lenses and prisms. A one diopter lens (1.00 DS) brings parallel rays of light to a point focus at a distance of one meter. A one diopter prism (1Δ) displaces the image of an object 1 centimeter at a one meter viewing distance.

Diplopia – the condition in which a single object is perceived as two objects instead of one, double vision. Diplopia may be “physiological,” which is the normal, desired perception of double vision of a non-fixated object, eg. the Brock String. Or it may be “pathological,” as in strabismus, when a fixated object is perceived as double because the strabismic eye is not aligned upon it; that is the image of the fixated object falls on a non-macular area of the deviated eye and is not suppressed. The simultaneous stimulation of non-corresponding or disparate retinal elements by a target causes the target to be localized in two different subjective visual directions, and thus appears double.

Directionality – the ability to correctly determine spatial directional properties of individuals, objects, and language symbols.

Dissociation – separating the binocular field into 2 monocular ones, for example when using dissociating prism to make the patient see double.

Divergence – the relaxation of convergence, allowing the two lines of sight to become nearer to parallel, as the object moves away, as BI prisms are introduced, or as the patient looks to a more distant target.

Divergence Excess – more exo is measured at far than at near.

Divergence Insufficiency – more eso is measured at far than at near. Dorsal – towards the back.

Duction – an eye movement involving only one eye (ie monocular).

9

Dynamic retinoscopy – retinoscopy performed while the patient fixates at near. The term dynamic is used because the patient's accommodation is active. This is in contrast to static retinoscopy, which is done while the patient fixates at distance, where theoretically accommodation is relaxed.

Eccentric Fixation – in amblyopia, the condition in which under monocular viewing the amblyopic eye uses a point other than the fovea for straight-ahead viewing.

Elevation – aiming the eyes upward.

Emmetropia – the condition under which an individual does not measure any refractive “error;” the patient sees well at distance without compensatory lenses, and sees blur when plus lenses are applied.

Enucleation – the surgical removal of the entire eye.

Esotropia – in strabismus, the condition in which one eye deviates inward while the other eye fixates.

Excycloversion – rotation of the eye around the anterior/posterior axis toward the temple.

Exotropia – in strabismus, the condition in which one eye deviates outward while the other eye fixates.

Extorsion – rotation temporalward.

Extra-ocular Muscles – six striated muscles that attach to the outside of each eye (total 12) and which allow the eye to move. These muscles coordinate together to produce eye movements in the different positions of gaze:

o Lateral rectus (LR) – abduction (away from the nose), innervated by Cranial Nerve VI (the Abducens)

o Medial Rectus (MR) – adduction (towards the nose), innervated by Cranial Nerve III (Oculo-motor)

o Superior Rectus (SR) – responsible for adduction, elevation, and intorsion, innervated by Cranial Nerve III

o Inferior Rectus (IR) – responsible for adduction, depression, and extorsion, innervated by Cranial Nerve III

o Inferior Oblique (IO) – responsible for abduction, elevation, and extorsion, innervated by Cranial Nerve Cranial Nerve III

o Superior Oblique (SO) – responsible for abduction, depression, and intorsion, innervated by Cranial Nerve IV (Trochlear).

10

 

Table and Diagram SummariesLR abduction abductionMR adduction adductionSR adduction elevation intorsion up and outIR adduction depression extorsion down and outIO abduction elevation extorsion up and inSO abduction depression intorsion down and in

Farpoint – the point upon which the visual axis of the eye is sharply imaged on the retina when accommodation is relaxed. The far point of a “normal” eye is said to be at optical infinity.

Fixation – the process, condition, or act of directing the eye toward an object of regard, causing the image of the object to be aligned on the fovea. During fixation there are small involuntary saccades, which are imperceptible to the naked eye; this means that fixation is an active process where the oculomotor system sends and receives information to the brain in order to keep the image centered on the fovea, where it will best be seen.

Fixation disparity – exists when there is a small misalignment of the eyes when viewing an object binocularly. Since the corresponding points still fall within Panum’s areas, the object is still seen as single. The misaligment may be vertical, horizontal or both. The misalignment (measured in minutes of arc) is much smaller than that of a strabismus, although it may reduce a patient's comfort and level of stereopsis. A patient may or may not have fixation disparity and a patient may have a different fixation disparity at distance than near.

Flipper – a lens carrier designed to hold two pairs of lenses, such as plus lenses on one side and minus on the other, or base-in prisms on one side and base-out prisms on the other side.

Fovea Centralis – a tiny spot in the center of the macular area of the eye which enjoys a high concentration of cones. Visual acuity is said to be the sharpest at the macula, and the eyes move to position the images of objects of regard on the fovea, as that is where they will be seen most clearly.

Frontal Lobe – sometimes referred to as the “executive” part of the brain, the functions of the frontal lobe involve the ability to recognize future consequences resulting from current actions, to choose between good and bad actions (or better and best), override and suppress unacceptable social responses, and determine similarities and differences between things or events.

The frontal lobes also play an important part in retaining longer term memories which are not task-based. These are often memories associated with emotions derived from input from the brain's limbic system. The frontal lobe modifies those emotions to generally fit socially acceptable norms,

11

Fusion – the unification of the individual images from each eye into a unified percept. Fusion has 2 components: sensory and motor.

o Sensory fusion refers to the single, unified percept that results when corresponding retinal areas are stimulated by images of the same object or images of compatible content. It is the ability to appreciate two similar or compatible images, one with each eye and interpret them as one. For sensory fusion to occur, the images not only must be located on corresponding retinal areas but also must be sufficiently similar in size, brightness and sharpness. Unequal images present a severe obstacle to fusion.

o Motor fusion differs in that it is the physical movement of the eyes to achieve a single image when presented with different retinal images to result in or to maintain sensory fusion. It is the ability to align the eyes in such a manner that sensory fusion can be maintained. The stimulus for these fusional eye movements is retinal disparity outside of Panum’s area and the eyes moving in opposite directions (vergence).

Thus, sensori-motor fusion refers to the quality and quantity of the binocular response.

Grades of Fusion – Worth divided binocular vision into grades, relative to the type of demand presented by a target.

o First degree Fusion, or Superimposition refers to the common localization of dissimilar but compatible images presented separately to each eye. An example of a first degree fusion target might be the Fish and the Bowl targets from the Mirror Stereoscope. One eye sees the fish, the other eye sees the bowl. When fusion occurs, the patient will see a fish in a fishbowl.

o Second degree Fusion, or Flat Fusion refers to the single simultaneous perception of identical targets, one presented to each eye. Upon examination of a second degree fusion target, the distance between all corresponding (homologous) points will be found to be the same. An example of a second degree fusion target might be the AN 1 card used in the Brewster stereoscope.

12

Most second degree fusion targets include a first degree fusion component that acts as a suppression control. An example of this might be the AN 2 stereoscopic card. In this target, each eye sees an identical star, but the right eye sees the odd numbers and the left eye sees the even numbers. When fusion occurs a single star with ALL of the numbers should be seen. The star, or second degree fusion component, may act as a “fusion lock,” enhancing or guiding binocular posture, and providing a “framework” for the simultaneous perception of the first degree fusion components.

o Third degree Fusion, or Stereopsis refers to the perception of depth when viewing targets that are designed with retinal disparity. Stereopsis per se is defined as the binocular appreciation of depth due to retinal disparity. Upon examination of a third degree fusion target, the distance between corresponding (homologous) points will vary, resulting in the perception of depth when fusion occurs. Although the distance between corresponding points varies, the differences are not great enough to prevent the entire target from being seen as single. An example of a third degree fusion target might be the Clown Vectogram; When the 2 films are super-imposed, the objects do not coincide exactly. This disparity is what gives rise to the perception of 3-D when the appropriate fusion response is made.

Hemianop

sia – literally, "half vision" a condition resulting from malfunction or damage to one side of the optic tract (see diagram below). Common causes of hemianopsia are stroke, trauma, and tumor. Hemianopsias may vary from an absolute loss of all vision on one side (light, form, and color), to a relative loss where vision is reduced, but not completely missing. Relative hemianopsias may vary from light or motion detection only in the impaired field to subtle decreases in sensitivity

13

only demonstrated on careful visual field testing. The location of damage or lesion along the visual pathway determines the type of field loss.

o Binasal hemianopsia – vision is missing in the inner half of both the right and left visual fields.

o Bitemporal hemianopsia – vision is missing in the outer half of both the right and left visual fields.

o Homonymous hemianopsia- a loss of vision in the same visual field of both eyes.

Hering-Bielschowsky After Image Test – a diagnostic test used to determine the status of Correspondence between the eyes.

Hering’s Law of Equal Innervation – normally our eyes move together in the same direction, called versional movement. Coordinated binocular eye movements require symmetrical innervation of the muscles of each eye. For example, when looking to the left, the left lateral rectus and right medial rectus muscles simultaneously contract, and the left medial rectus and right lateral rectus muscles relax. Hering’s law states that yoke muscles receive equal innervation. In the example above, the left lateral and right medial rectus muscles are yoke agonist (contracting) muscles. The left medial and right lateral rectus muscles are yoke antagonist (extensor and flexor) muscles.

Hippocampus – a brain structure located inside the medial temporal lobe of the cerebral cortex. It belongs to the limbic system and plays a major role in short

14

term memory and spatial navigation. In Alzheimer's disease the hippocampus is one of the first regions of the brain to suffer damage; memory problems and disorientation appear among the first symptoms. Damage to the hippocampus can also result from oxygen starvation (anoxia), encephalitis, or medial temporal lobe epilepsy. People with extensive hippocampal damage may experience amnesia, that is, inability to form or retain new memories.

Hirschberg Test – a screening test that can be used to detect the presence of strabismus. It is performed by shining a penlight in the person’s eyes and observing where the light reflects off the corneas. With normal ocular alignment the light lands on the center of both corneas. In exotropia the light lands on the medial aspect of the cornea. In esotropia the light lands on the lateral aspect of the cornea. In hypertropia the light lands on the inferior aspect of the cornea. In hypotropia the light lands on the superior aspect of the cornea.

Horopter – (horizon of vision) the sum total of points in space which can be seen as single by the two eyes. It is defined as the locus of all points that are imaged on corresponding retinal elements at a given fixation distance. Thus a line can be drawn through the object of regard such that all the points on the line are imaged on the corresponding retinal elements and are seen singly. All the points not lying on the horopter are imaged by disparate retinal elements and are seen as double. This diplopia elicited by object points off the horopter is called “physiological diplopia.”

Hyperopia - also called farsightedness, the condition in which in the uncorrected eye, light rays come to point focus behind the retina. Hyperopia is compensated for by the use of plus lenses.

15

Hyperphoria – the tendency of one eye to aim higher than the other.

Hypertropia – in strabismus, the condition in which one eye deviates or aims upward, while the other eye fixates.

Hypophoria – the tendency of one eye to aim lower than the other.

Hypotropia – in strabismus, the condition in which one eye deviates or aims downward, while the other eye fixates.

Incycloduction – the rotation of the eye around the anterior/posterior axis toward the nose.

Inferior – lower.

Intermittent – not constant. In strabismus the deviation is manifested irregularly, i.e. it is not always present. There are times and conditions when the eyes are aligned.

Intorsion – rotation nasalward.

Iris – the colored tissue surrounding the pupil which is involved in regulating the amount of light that enters the eye.

Isometropia – the condition in which both eyes have equal or nearly equal refractive status. Just Noticeable Difference (JND) – the smallest amount of change that can be made with the patient being aware of the change. The smaller the JND, the better the patient is at making fine discriminations.

Krimsky Test – a test of binocular motor alignment by which a penlight is shone at the eyes and the position of the light reflex centered with a prism, thus indicating the amount of deviation.

Lag of Accommodation - when presented either with near targets or with minus lenses placed in front of the eyes, most individuals accommodate less than is needed to bring the target into focus. This under-accommodation is referred to as the lag of accommodation and is quantified by the difference between the actual accommodative stimulus and the measured accommodative response.

Laterality – the individual’s ability to understand and identify right and left on his/her own body.

Lateral Geniculate Nucleus (LGN) – one of the primary processing centers for visual information received from the retina of the eye. The LGN is located inside the thalamus of the brain, and is part of the central nervous system. The LGN receives information directly from the retinal ganglion cells via the optic nerve and from the reticular activating system. Neurons of the LGN send their axons through the the optic radiations, a pathway directly to the primary visual cortex, also known as the striate cortex, in the occipital lobe.

16

The LGN is where the process of co-ordinating vision from the two eyes starts, and it acts as a sort of “filter,” determining what and how much information goes to visual cortex. In addition, the LGN receives many strong feedback connections from the primary visual cortex, i.e. information travels in both directions..

Localization – part of the process that helps the individual to identify the “where is it?” of objects in space.

Lustre – also spelled “Luster,” refers to the appearance of 2 different colors, usually red and green, that when viewed simultaneously and superimposed, result in a mix of color, which is often unstable, and frequently described as “muddy brown,” or “orange” and having a glossy or metallic quality.

Macula – an area in the back of the retina, located temporally and slightly below the optic nerve head. The macula contains the fovea centralis.

Macular Integrity Tester (MIT) – an instrument that provides feeback of the location in space where the fovea is aiming. It is useful in testing for and traing Eccentric Fixation.

Maddox Rod – an instrument used by the optometrist in measuring the alignment of the eyes.

Meter – a unit of measurement used in the metric system. One meter is equivalent to 39.37 inches.

Millimeter – one-thousandth of a meter; there are approximately 25 millimeters to the inch.

Minus Lens - also called “concave.” A minus lens changes the path of light so that the focus is on the same side of the lens as is the object, and closer to the lens than the object. A minus lens makes objects of regard appear smaller and closer (the SI of SILO).

Monocular – pertaining to vision with one eye alone.

Monocular Cues to Depth – our ability to appreciate depth comes from both monocular and binocular information. Monocular cues that help us determine relative distances of things include:

Apparent size – small retinal objects are interpreted as distant objects and large retinal objects as near objects. Objects progressively increase in size as they move towards us (looming).

Interposition – relatively nearer objects tend to conceal or overlay more distant objects.

Aerial perspective – water vapor, dust and smoke in the atmosphere scatter light and make distant objects indistinct and relatively color desaturated.

Shading – light falling on solid objects causes shadows to be cast, and on curved surfaces causes a gradation in the intensity of shadow.

17

Geometric perspective – physically parallel lines converge toward a vanishing point at the horizon, e.g. railroad tracks.

Relative velocity – the image velocity of a moving target in the distance is lower than the image velocity of the same moving target when it is nearby.

Motion parallax – movement of the head cause the images of near objects to move opposite the head and the images of far objects to move with the head, assuming the fixation point is at an intermediate distance.

Monocular Fixation in a Binocular Field (MFBF) – used frequently in Amblyopia therapy, it is a created situation where both eyes receive the peripheral information, while the amblyopic eye is presented with a detailed, central task that it alone can perceive. MFBF is used as a “bridge” between monocular and binocular activities and is used to over-ride the tendency of the “good eye” to exert active cortical inhibition over the amblyopic eye.

Myopia – also called “nearsightedness.” The condition in which in the uncorrected eye, light rays come to point focus in front of the retina. Myopia is compensated for by minus lenses.

Nasal – towards the nose.

Near Point of Convergence (NPC) – the closest point that an object of regard can be moved toward the nose without loss of fusion.

Neglect (also called Visual Neglect, Hemispatial agnosia, Visual/spatial Neglect, or Hemi-imperception) – caused by injury from a stroke or other trauma, neglect is a passive unconscious decreased awareness of part of the field of view or other stimuli to one side of the body. It usually occurs with a visual field defect, but may also occur in the absence of field loss. A person with a visual field loss would be aware of the area of loss and likely to make compensations. A person with both visual field loss and visual neglect would unconsciously neglect the area of the field loss and be less likely to compensate for the defect.Damage to the right side of the brain may cause both visual field loss and visual neglect to the left side. Right brain injury neglect is usually more severe than left brain injury neglect. The most common site for visual neglect is the parietal lobe, but damage to frontal lobe and even the deeper structures (thalamus and basal ganglia) may cause it.

Noncomitant – or incomitant, or non-comitant, in strabismus the condition in which the angle of deviation is not constant, but varies according to position of gaze. This may be due to a paresis or paralysis of one or more of the extra-ocular muscles, or from scar tissue after surgery.

Nystagmus - refers to rapid involuntary movements of the eyes that may be from side to side (horizontal nystagmus), up and down (vertical nystagmus) or rotary. Depending on the cause, these movements may be in both eyes or in just one eye. The involuntary eye movements of nystagmus are caused by abnormal function in the areas of the brain that control eye movements. The exact nature of these disorders is poorly understood. Nystagmus may be either congenital (present at birth) or may be acquired (caused by disease or injury later in life).

18

Objective – a test or finding that does not require a patient response.

Objective Angle – in strabismus, refers to the angle by which the line of sight of the deviated eye fails to intersect the fixation target; that is the angle between the lines of sight of the deviating eye and the fixating eye. The objective angle is measured by an objective method, such as corneal reflexes or the unilateral cover test with prisms.

Occipital Lobe - The occipital lobe is the visual processing center of the mammalian brain, and is the location of the primary visual cortex. It contains regions specialized for different visual tasks, such as visuo-spatial processing, color discrimination and motion perception.

Occluder – also called “eye patch,” it is a device used to cover or occlude an eye, thus interfering in the transmission of light through that eye. An occluder may provide total or partial blockage of light and/or form.

Oculomotor Triad – the oculomotor triad consists of ocular accommodation, vergence, and pupil size, and is essential to seeing a clear, single, and controlled image of the outside world.

O.D. – from the Latin, “Oculus Dexter,” abbreviation meaning right eye.

O.S. – from the Latin, “Oculus Sinister,” abbreviation meaning left eye.

O.U. – from the Latin, “Oculi Uterque,” abbreviation meaning both eyes together.

Ophthalmic – pertaining to the eye.

Ophthalmology – medical specialty that deals with diseases of the eye and eye surgery.

Ophthalmoscope – a hand-held instrument used for viewing the interior of the eye. Ophthalmoscopy is part of the eye health evaluation.

Optic Chiasm – The optic nerves from both eyes meet and cross at the optic chiasm at the base of the hypothalamus of the brain. At this point the information coming from both eyes is combined and then splits according to the visual field. The corresponding halves of the field of view (right and left) are sent to the left and right halves of the brain, respectively, to be processed. That is, the right side of primary visual cortex deals with the left half of the field of view from both eyes, and similarly for the left brain. A small region in the center of the field of view is processed redundantly by both halves of the brain.

19

Optic Nerve – part of the nervous system that transmits the impulses of sight from the retina along the visual pathways. There are currently 11 known branches of the optic nerve.

Optokinetic Nystagmus (OKN) - OKN is based on the principle that the eyes tend to follow or track the motion of one element at a time in a steadily moving display. As the tracked element moves out of sight, the eyes will "snap back" to fixate and follow another one. This subcortically-mediated function is termed optokinetic nystagmus (OKN) and is present at about five days after birth. This response can be used as an objective measure of an infant's ability to see detail in a moving stimulus, such as a bar grating or OKN drum. The absence of an OKN response suggests that the infant may not perceive the elements of the moving target as separate.

Organic – caused by a pathological or anatomical problem.

Orientation – part of the process that helps the individual identify and understand “where am I?” in space.

Orthophoria – the condition in which the position of the eyes is not changed when binocularity is broken or interrupted, as during an alternate cover test. The doctor will see no movement upon removing the occluder.

Paired Cranial Nerves – twelve pairs of nerves that emanate from the nervous tissue of the brain, and which ultimately exit/enter the cranium through openings in the skull; thus their name is derived from this association with the cranium. Motor components of the cranial nerves are derived from cells located in the brain.  These cells send axons out of the cranium where they ultimately control muscle (e.g., eye movements), glandular tissue (e.g., salivary glands) or specialized muscle (e.g., heart or stomach). Sensory components of cranial nerves originate from collections of cells that are located outside the brain. These collections of nerve cells bodies are called sensory ganglia.

20

Palpebral Fissure – the area of the eye seen when the lids are open.

Panum’s Areas – in reality Correspondence between the 2 eyes does not occur rigidly, point by point. To each retinal point there is a small elliptic-shaped zone in which an image may fall and still give rise to a common visual direction when stimulated simultaneously with a specific retinal point in the other eye. These zones are called Panum’s areas, and are smaller at the fovea, increasing in size in peripheral retina. This helps to explain why a strabismic may experience gross peripheral fusion even though the eye is deviated.

The increase in the spatial extent of Panum’s area in the peripheral visual field serves three useful purposes:

Increasing size of Panum’s area matches increasing coarseness of peripheral vision. Receptive field size increases and the visual acuity decreases as a function of eccentricity.

Increasing the thickness of Panum’s area prevents peripheral diplopia when fixating flat targets held at close range.

21Cranial Nerve:        Major Functions:

I Olfactory        smell

II Optic        vision

III Oculomotor        eye movement and pupil dilation

IV Trochlear        innervates superior oblique, turns eye down and in

V Trigeminal        chewing somatosensory information from the face & mouthtouch & pain

VI Abducens        moves eye temporally

VII Facial        controls most facial expressions secretion of tears & salivataste, somatosensory information from ear

VIII Vestibulocochlear(auditory)

       hearing equillibrium and balance

IX Glossopharyngeal        taste (posterior 1/3 of tongue) somatosensory information from tongue, tonsils, pharynx; controls some muscles used in swallowing

X Vagus        sensory, motor, and autonomic functions of viscera (glands, digestion, heart)

XI Spinal Accessory        controls trapezius & sternocleidomastoidcontrols swallowing movements controls muscles used in head movement.

XII Hypoglossal        controls tongue movements

Increasing the extent of Panum’s area peripherally makes cyclofusion possible despite cyclovergence errors of as much as 2 degrees between the two eyes.

Panum’s area expands and contracts depending on the size, sharpness and speed of the stimuli.

Parallax – the apparent displacement of an observed object due to a change in the position of the observer. In the real world, parallax is an important cue to depth, and using parallax one can determine the relative distance of objects. Prisms and filters can be used to produce a parallax-like effect in the therapy room (called paradoxical parallax), which evaluates the patient’s ability to respond appropriately to visual information.

Paralysis – the complete loss of muscle function of one or more muscle groups. Paralysis often includes loss of feeling in the affected area.

Paramacular – referring to the area immediately adjacent to and surrounding the macula.

Paresis – a condition typified by partial loss of movement, or impaired movement. In the optometric sense it is usually used to describe the muscles of the eyes.

Parietal Lobe – an area of the brain involved in the visual process. It is currently believed that the majority of the Magnocellular fibers travel to the parietal lobe via the dorsal stream. The parietal lobe deals with somatosensory information (kinesthesis and body awareness), cognition, information processing, pain and touch sensation, spatial orientation, speech, visual perception, timing, and movement. It integrates sensory information from different modalities, particularly determining spatial sense and navigation.

22

Parasympathetic Nervous System – a part of the Autonomic Nervous System. The parasympathetic system returns the body functions to normal after they have been altered by sympathetic stimulation. In times of danger, the sympathetic system prepares the body for violent activity. The parasympathetic system reverses these changes when the danger is over. These changes include: slowing of heart beat, lowering of blood pressure, constriction of the pupils, increased blood flow to the skin and viscera, resumption of peristalsis in the GI tract.

P.D. – also called inter-pupillary distance, refers to the distance, expressed in millimeters, between the pupils of the patient’s eyes.

Perimeter- an instrument used to evaluate the central and peripheral fields of vision.

Periodicity – in strabismus, referring to the distances at which the deviation is manifest.

Phoria – the natural “resting position” of the eyes when they are not viewing the same object at the same time. A phoria represents a “mismatch” between where objects really are and where the person judges them to be.

Photophobia – excessive sensitivity to light, which may include aversion to sunlight and well-lit places.

Plegia - paralysis in which all movement is lost.

Point Zero – in strabismus, this is Jampolsky’s term to define the point on the retina of the deviating eye which receives the image of the object fixated by the fovea of the non-strabismic eye when no vergence demand is present.

Polaroid filters – are special filters which allow full transmission of light in one direction, gradually reducing the amount of transmission to “zero” at a point 90 degrees away. By using a pair of Polaroid glasses with 2 filters oriented in opposite directions from each other and a special set of Polaroid targets we can control the information that is available to each eye. Targets using Polaroid are usually designed to provide a stereoscopic 3-D effect by using 2 similar images which are slightly offset from each other. When viewed through Polaroid glasses they produce a unified stereoscopic image.

Post Traumatic Vision Syndrome (PTVS) – following a TBI, a patient may develop a constellation of symptoms that may include, but are not limited to: blurry vision, diplopia, headaches, spatial disorientation, photophobia, visual hallucinations, poor attention and concentration, and poor visual memory. Conditions often associated with PTVS include convergence insufficiency, accommodative dysfunction, exotropia or exophoria, low blink rate, and poor ocular motility.

Primary Visual Direction (PVD) – the “straight ahead” oculo-centric location normally determined by the fovea of the non-deviated eye, and from which all

23

other spatial determinations are made. A foveally fixated point is interpreted by the individual as being straight ahead, and the other objects in the visual field are experienced as being located above, below, to the side of, etc. the foveally fixated point. Thus, each retinal element has its own subjective visual direction. PVD is associated with the fovea, and is therefore called oculo-centric. This is in distinction to visual direction with respect to the head, which is called ego-centric. If fixation movements are made while the head remains still, oculo-centric direction for each fovea does not change, but ego-centric direction does.

Prism – a wedge shaped lens that changes the direction of light passing through it, but does not change focus. Light entering a prism is deviated toward the base (the thickest portion), and the image of the object being viewed appears to move in the direction of the apex (the point). Prisms are typically designed by the direction of their bases: Base Up, Base Down, Base Right, or Base Left. When used on a binocular basis, they are commonly referred to as Base In (both bases in toward the nose) or Base Out (both bases out towards the ears). Yoked prism refers to the application of prism when the bases of both prisms are oriented in the same direction, i.e. both Bases Up, Bases Down, Bases Right, Bases Left.

Prism can be used in a compensatory way, helping to achieve alignment of the eyes when it is not possible by other means. In the therapy room prisms are also used therapeutically on both a monocular and binocular basis to create a mismatch between the objects in the real world, and where the prisms, because of the way they displace light, cause the visual system to perceive them to be. As the patient resolves these mismatches, he/she learns to use vision in a new, more efficient way. On a binocular basis, they change the demand for convergence in order to keep a target single, and reflexly change accommodation.

Yoked prisms (when the bases of both prisms face in the same direction) are used in vision therapy to help disrupt the normal association between the vestibular and visual systems, and create greater demands for re-orientation in space to compensate for the shift of gravity, postural changes, and sense of orientation imposed by the prisms. These types of prisms can be base right (BR), base left (BL), base up (BU), or base down (BD). When the bases of the prisms are facing the same direction over each eye, the space observed is displaced towards the direction of the apex. This disruption of reality causes the patient to readjust or shift his/her center of gravity to account for the change in position of the space. In addition to the apparent shift in space, yoked prisms in the base up and base down positions can create the illusion of an increase or

24

decrease of the volume of space. In other words, a room will appear to be longer or shorter than it really is when seen through these yoked prisms. Because the visual system is so dominant compared to other systems in the body, the patient will often change gait, head or general body posture, or recalibrate perceived spatial relationships to appropriately match the demands of the “new” reality. Yoked prisms can also play a vital role in therapy for an ABI patient. For example, if a patient constantly perceives the world being shifted to the right, yoked prisms may help “realign” that space for that individual, thus re-establishing a sense of stability and orientation. Other applications of yoked prism include patients with autism, attentional difficulties, with Cerebral Palsy, etc.

Special types of prism (called Peli prisms) can also be incorporated into spectacle lenses, and used as an “alerting” mechanism for patients with visual field defects.

Propioception – a distinct sensory modality that provides feedback solely on the status of the body internally. It is the sense that indicates whether the body is moving with required effort, as well as the reative position of parts of the body, and where they are located in relation to each other.

Pupillary responses – observed responses of the pupils in response to certain stimuli. There are 3 pupillary responses which affect both eyes, even if only one eye is stimulated:

o Direct – the pupil of the eye constricts (gets smaller) when a light is shone into that eye.

o Consensual – the pupil of the fellow eye also constricts when a light is shone into an eye

o Accommodative – the pupils constrict in response to the stimulation of accommdation

Pursuit – the type of eye movement used when following a moving target, to keep the image of the object of regard on the fovea. Pursuits are believed to be mediated in the occipital lobe. The primary stimulus to initiate a pursuit is the speed of the object. Pursuits are relatively slow eye movements (compared to the relative speed of saccades) that involve smoothly tracking a moving target while maintaining an accurate fixation. It is often called a “holding movement” because it allows the patient to hold or maintain the desired target on the fovea. Pursuits allow the individual to extract information from a dynamic and changing environment. The patient has the ability to alter the speed or duration of a pursuit during its progression, whereas that is not possible in a saccade. Before an

25

efficient pursuit can be achieved, one must possess the ability to make and hold a fixation.

Accurate maintenance of fixation on the moving object is accomplished by a combination of smooth pursuits and saccades. When the object is moving faster than the pursuit system can keep pace, the faster saccade system is activated to reduce retinal slip and reposition the object of regard on the fovea. Even though the image is moving, our sensory system adjusts so that we maintain the sense of straight- ahead and the visual perception of the world remains continuous and stable

Recovery – the point at which fusion is regained once broken.

Re-fixation reflex – in the normal eye, the image of a fixated target is centered on the fovea, as that is where it will best be seen. If you are looking to the side of an object instead of directly at it (eg. if you have made an inaccurate saccade, or if a fixated target suddenly moves), it is signaled that the image of the object of regard is blurry, and not viewed straight ahead. The re-fixation reflex at the fovea is stimulated as this “error” of eye position is registered, and the eye makes a corrective movement to put the image back on the fovea. This reflex allows foveal re-fixation from target to target, and maintenance of foveal fixation on a moving target.

Reticular Formation – The reticular formation is a part of the brain that is involved in actions such as awaking/sleeping cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli. It is essential for governing some of the basic functions of higher organisms, and is one of the oldest portions of the brain. It is an important regulator in the autonomic nervous system for such processes as respiration rate, heart rate, and gastrointestinal activity, and also plays an important role in sleep and consciousness as well as modulation of pain. The reticular formation been shown to play a major role in alertness, fatigue, and motivation to perform various activities. Researchers have speculated that the reticular formation controls approximately 25 specific behaviors, including sleeping, walking, eating, urination, defecation, and sexual activity.

Reticular Activating System is the name given to the part of the brain (the reticular formation and its connections) believed to be the center of arousal and motivation in mammals, including humans.The activity of this system is crucial for maintaining the state of consciousness. Although the functioning of this system is a prerequisite for consciousness to occur, it is generally assumed that this system's role is indirect and it does not, by itself, generate consciousness. Instead, its unique anatomical and physiological characteristics ensure that the thalamocortical system fire in such a way that is compatible with conscious experience. It is also involved with the Circadian Rhythm. It is thought to be the area affected by many psychotropic drugs. General anesthetics work through their effect on the reticular formation.

26

Retinal Rivalry – occurs when 2 very different (conflicting) Images are simultaneously and separately presented to the two eyes. Under normal conditions, the brain will alternately suppress one image, then the other.

Retinoscope – a hand-held instrument that gives the optometrist information regarding the refractive status of an eye. Observation of the retinoscopic reflex also provides valuable information regarding attention, visual posture, and embededness of the visual posture.

Rod - a light-sensitive retinal receptor found in great abundance in peripheral retina. The rods are responsible for dim illumination (scotopic) seeing and motion detection. Rods transform light information into chemical energy so that it can be used by the visual system.

Saccades – A saccade is a relatively quick eye movement (compared to the relative slow speed of pursuit movements) during which the eye “jumps” from one target to another. Saccadic eye movements are thought to be mediated by the parietal lobe and the eyefields in the frontal lobe. The primary stimulus for a saccadic eye movement is the location of the target. It is often called a “catching” movement because it helps the patient “catch” and bring a new target to the fovea. It is faster than all the other eye movements and always starts and ends with a fixation. Like the pursuit, it requires the patient to have the initial ability of maintaining a fixation. Thereafter, the concept of peripheral awareness and the ability to “calculate” the size of the jump needed to arrive at the desired target play a key role in accurate and efficient saccades.

Sclera – the tough, fibrous white outer tunic (coat) of the eye, a continuation forward of the dura matter of the brain covering, where the 6 extra-ocular muscles are attached. Unlike the cornea, the sclera contains blood vessels.

Scotoma – an area within the visual field in which vision is absent or reduced; it may be the result of disease, neurological insult, or prolonged suppression.

Sherrington’s Law of Reciprocal Innervation – a law that explains agonist-antogonist relationships, and monocular eye movements (ductions). It states that when a muscle contracts, its direct antagonist relaxes to an equal extent allowing smooth movement.

27

Sight – or eyesight, relates to visual acuity, the sharpness of vision, or how well a person is able to resolve letters on the Snellen chart, often expressed as a Snellen fraction, eg. 20/20, 20/40, etc. It gives no information as to how much effort is needed to see clearly, to use both eyes together, or how much meaning is obtained from the visual input.

Signs – optometric findings or observations resulting from a visual problem.

SILO – acronym for Small In, Large Out. SILO relates to perceived changes induced by the introduction of lenses or prisms. SILO may be induced by lenses, prisms, target separation, and after-images.

Single Vision – can be classified as:

1. Normal – when it is bifoveal and there is no manifest deviation.

2. Anomalous – when the images of the fixated object are projected from the fovea of one eye and an extrafoveal area of the other eye i.e. when the visual direction of the retinal elements is different. A small manifest strabismus is therefore always present in anomalous single vision.

Snellen Chart – a standard chart of letters used to measure visual acuity.

Spastic – jerky, in VT often used to describe the quality of poor eye movements.

Spatial – of or pertaining to space, or location in space.

Sphere – a lens with equal power in all meridians.

Stereopsis – the binocular appreciation of depth due to retinal disparity (see also Third degree fusion). The eyes are separated in the horizontal plane of the head and thus each eye has a slightly horizontally disparate view of the world. The sensory fusion of these horizontally disparate unequal retinal images results in a three dimensional percept.

Stereoscope – an instrument designed to separate the binocular field into 2 parts, one part for each eye. When fusion is attained, a unified image is seen. It is used to explore both binocular and monocular abilities when both eyes are open. There 2 most common types of stereoscope are Brewster (which uses sphero-prisms), and Wheatstone (which uses mirrors).

Strabismus – or “squint,” or “tropia” refers to the visual condition in which binocular (bi-foveal) fixation is not present. When strabismus is present (manifest), the visual axes of the eyes are not directed toward the same object at the same time. The line of sight of one eye does not intersect the target being observed.

Streff Syndrome – also called “Juvenile Bilateral Functional Amblyopia” or the “Non-Malingering Syndrome,” named after Dr. John Streff. It is a bilateral

28

condition in which there is reduced visual acuity at both distance and near in the presence of minimal refractive error and no evidence of lesion or pathology. The visual acuity at near is more reduced than at distance. Measured VAs may be variable, and may be better with single letters than with full chart or full line presentation. Subjective complaints are usually related to near-point tasks such as reading. Frequently patients will have reduced stereopsis, large accommodative lag on dynamic retinoscopy, and a reduced visual field (tubular or spiral field), that may be variable. There may be difficulties with eye-hand coordination, fixation difficulties, and color vision disturbances. The patient’s general behavior may seem out-of-step or off in timing. Prior to the onset of the condition, most children have been above-average achievers. The syndrome may be associated with a visual or emotional stress occurring in the child's life. It is more prominent during puberty (ages 7-13), girls more frequently than boys. Treatment includes low plus lenses and/or vision therapy. This condition is sometimes incorrectly diagnosed by doctors as Hysterical Amblyopia.

Stress – any condition that causes the organism to make an adaptation.

Subjective – a test or finding based on the patient’s reported personal reaction and ability to respond.

Subjective Angle – in strabismus, the point at which the patient reports a first degree fusion response or higher. In Normal Correspondence the Subjective Angle of strabismus is equal to or within a few degrees of the Objective Angle.

Superior Colliculus (SC) – one of the primary processing centers for visual information received from the retina of the eye. A percentage of the magnocellular fibers that leave the back of the eye do not go to the LGN, but instead to the Superior Colliculus in the mid-brain. In the SC visual information integrates with vestibular information from the semicircular canals, propioceptive information from muscles, tendons, and ligaments, tactile, auditory, and other systems. It is involved in orientation, balance, and postural mechanisms, and keeps the world level. It is part of the process that tells us whether we are moving, the object of regard is moving, or both are moving. Using this information, along with information from other areas of the brain, we construct a personal 3-D representation of space, with ourselves placed at the center.

Suppression – refers to the condition where all or part of the visual field is not perceived. Suppression occurs upon the simultaneous stimulation of both eyes, as the main “purpose” of suppression is to secure single vision where it would not be attainable otherwise. Suppression may be classified as active or passive.

o Active suppression is suppression that occurs when single binocular vision is not attainable to avoid diplopia and visual confusion.

o Passive suppression is suppression that occurs due to gross inequalties in the visual information between the eyes, as in Anisometropia or Amblyopia. Passive suppression is generally thought to be more shallow than active suppression, as it takes less effort for the brain to ignore a blurry image than to suppress a double image. For this reason, passive suppression is often thought to be easier to eliminate.

29

Sympathetic Nervous System – part of the Autonomic Nervous System. It is always active at a basal level, and becomes more active during times of stress. Its actions during the stress response comprise the “fight-or-flight” response, which includes the release of adrenaline and cortisol into the system (the stress hormones), increase in the rate of breathing, particularly in the upper lobes of the lungs (hyperventilation), increase in heart rate, rise in blood pressure, reddening of the skin, pupil dilation, stimulates the conversion of liver glycogen into glucose, shunts blood away from the skin and viscera to the skeletal muscles, brain, and heart, inhibits peristalsis in the gastrointestinal (GI) tract, and inhibits contraction of the bladder and rectum.

Symptoms – a patient’s personal and subjective report to perceived departure from “normal,” eg. blurry vision, headaches, losing place when reading.

Synoptophore – (also called troposcope) an instrument that can be used in the diagnosis and treatment of strabismus.

Traumatic Brain Injury (TBI) – occurs when an outside force traumatically injures the brain. TBI can be classified based on severity, mechanism (closed or penetrating head injury), or other features (e.g. occurring in a specific location or over a widespread area). Head injury usually refers to TBI, but is a broader category because it can involve damage to structures other than the brain, such as the scalp and skull.

Brain trauma can be caused by a direct impact or by acceleration alone. In addition to the damage caused at the moment of injury, brain trauma causes secondary injury, a variety of events that take place in the minutes and days following the injury. These processes, which include alterations in cerebral blood flow and the pressure within the skull, contribute substantially to the damage from the initial injury.

TBI can cause a host of physical, cognitive, emotional, and behavioral effects, and the outcome can range from complete recovery to permanent disability or death. The 20th century has seen critical developments in diagnosis and treatment which have decreased death rates and improved outcome. These include imaging techniques such as computed tomography and magnetic resonance imaging. Depending on the injury, treatment required may be minimal or may include interventions such as medications and emergency surgery. Vision therapy, lenses, physical therapy, speech therapy, and occupational therapy may be employed for rehabilitation.

Temporal Lobe – An area of the brain involved in the visual process. The Parvocellular fibers travel to the temporal lobe via the ventral stream. The temporal lobe is involved with auditory processing, semantics, memory formation, object perception and recognition, naming and verbal memory, comprehension and significance, and high-level visual processing of complex stimuli such as faces, scenes, etc.

Tropia – strabismus, a suffix indicating a mis-alignment of the eyes. Usually combined with prefixes such as eso, exo, hyper, hypo, or cyclo.

30

Unilateral – one-sided; in strabismus it refers to the condition in which the same eye always deviates.

“V pattern” – a horizontal deviation may be different in upgaze versus downgaze. A “V pattern” deviation shows shows more eso (or less exo) in downgaze.

Ventral – towards the abdomen.

Vergences - eye movements involving both eyes in which each eye moves in opposite directions (“disjunctive” movements). Vergence movements help us to attain and maintain fusion by changing the alignment of the eyes.

Versions – teamed eye movements in which each eye moves in the same direction, sometimes referred to as “conjugate” movements.

Vestibular System – the sensory system that provides the dominant input about movement and equilibrium. The vestibular system comprises two components: the semicircular canals, which indicate rotational movements; and the otoliths, which indicate linear accelerations. The vestibular system sends signals primarily to the neural structures that control our eye movements, and to the muscles that keep us upright. The projections to the former provide the anatomical basis of the vestibulo-ocular reflex, which is required for clear vision; and the projections to the muscles that control our posture are necessary to keep us upright.

Vestibulo-ocular reflex (VOR) – a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual field. For example, when the head moves to the right, the eyes move to the left, and vice versa. Since slight head movements are present all the time, the VOR is very important for stabilizing vision: patients whose VOR is impaired find it difficult to read using print, because they cannot stabilize the eyes during small head tremors. The VOR does not depend on visual input and works even in total darkness or when the eyes are closed.

Vision – the process whereby the person obtains meaning from light information; the understanding of what is being seen that enables us to locate objects in space (where), judge size, distance, color, and movement.

Visual Axis – the main line of sight which extends from the fovea to the object of regard.

Visual Discrimination – the ability to visually distinguish similarities and differences.

Visual Figure Ground – the ability to perceive a form, and to locate it when embedded within other forms.

31

Visual Form Constancy – the ability to see the essential elements of a form, and identify them within other forms that may be smaller, larger, rotated, reversed or hidden within other designs.

Visual Memory: The ability to remember the characteristics of a given form after a brief presentation.

Visual Midline Shift – a dysfunction of the ambient (magnocellular) visual process that causes the individual to misperceive their position in the spatial environment. The shift may be lateral or anterior-posterior, and will frequently cause the person to lean to one side, forward, and/or backward. It can affect weight bearing for ambulation, and can occur in conjunction with a hemiparesis (paralysis to one side) following a TBI or stroke.

Visual Motor Integration – the ability to take in, analyze, and reproduce visual information using paper and pencil.

Visual Pathways – there are 2 main pathways that carry visual information from the eye to the brain: the Parvocellular/Focal pathway and the Magnocellular/Ambient pathway. These are parallel processing pathways eachdesigned to process different types of visual information. Neither system functions in isolation of the other or without neural information from the rest of the body. Optimally, both the focal and ambient visual systems reinforce one another and function synergistically. The dichotomy of the magno/parvo pathways is referred to as the the "where/what" or "action/perception" pathways by Goodale and Milner.

• M Cells (magnocellular) are mostly found in peripheral retina and comprise approximately 20% of the retinal ganglion cells. They are large and quick to respond, sampling a large number of temporal inputs over a short period of time. As a result, they provide good temporal resolution for information regarding space and movement. As a result is we do not see space as a series of individual snapshots of space separated in time, but rather it is perceived as a continual and uninterrupted flow of movement.

The magnocellular visual system is involved with spatial vision: orientation (where am I?), localization (where is it?), and timing (when?).

Goodale and Milner also term the magnocellular system a “how to” system, as it provides information on “how to” act on objects.

P Cells (parvocellular) are smaller, slower, and most heavily concentrated in the foveal area. They comprise approximately 80% of the retinal ganglion cells. They receive input from a relatively small number of photoreceptors, allowing for good detail-oriented resolution.

The parvocellular system is involved with object vision: detail and identification (what is it?). In an undamaged and well-functioning visual

32

system, object localization (“where?”) typically precedes object identification (“what?”).

Brief Summary of the Magnocellular and Parvocellular Systems:

MAGNOCELLULAR/AMBIENT PARVOCELLULAR/FOCALPrimarily peripheral Primarily macular and paramacularPrimarily functions at a subliminal or subconscious level

Primarily functions at a liminal or conscious level

Orientation in relation to space and time Detailed recognition of symbols, objects, faces, and locations

Balance +/- dynamic postural changes in relation to eye movements, coupled with the Oculo-Vestibular-Cervical Triad and all other senses

Comparisons of familiar shapes, sizes, forms, textures, colors, symbols, or faces to our memory of familiar, unfamiliar, or similar items

Movement detection par excellence, which guides us in all of our behaviors

Serial processing of letters, words, or objects for recognition and memory storage

Enables us to anticipate change in relation to movement, balance, and posture, and our dynamic environment

Visual completion, i.e. only needing to see part of an object or face to recognize the whole

The primary sense that enables us to have an anticipatory and adaptive nervous system

Functions with the prefrontal lobe “working memory” centers and frontal eye fields. Detailed memory of the immediate environment, including the placement of objects previously used

Global awareness of our surroundings, people, objects, and structures, and the ability to navigate through or around them to obtain a goal or reach a destination

It is estimated that 70-90% of our memory of facts occurs through this system

Visual Sequential Memory – the ability to remember for immediate recall a series of forms in their specific order of presentation.

Visual Spatial Relationships – the ability to see differences among forms when all or a part of a form has a different spatial orientation.

Visualization – the ability to form mental ideas or images in “your mind’s eye,” to retain them for future recall, or for synthesizing into new mental images beyond current or past direct experience.

Vitreous - a thick, transparent substance that fills the center of the eye. It is composed mainly of water and comprises about 2/3 of the eye's volume, giving it form and shape. The vitreous helps to keep the retina in place.

“X pattern” – decreasing convergence from the primary position in both upward and downward gaze.

33

Sources of definitions and images: Dr. Lynn Hellerstein, Dr. Paolo Tacconella, Dr. John Streff, Dr. Robert Kraskin, Dr. Kenneth Ciuffeda, Dr. William Padula, Dr. Gunter Von Noorden, Dr. John Griffin, Dr. Irvin Borish, Dr. Max Schapero, Dr. Israel Greenwald, the Drs. Hugonnier, Dr. Leonard Press, Dr. Theodore Grosvenor, Dr. Rahul Bhola, Dr. Robert Sanet, Dr. Penelope Suter, Tom Headline, COVT, Vicki Bedes, COVT, Irene Wahlmeier, COVT, Gabe Perea, COVT, Phuong Nguyen, OTR/L, personal class and seminar notes and writings, NORA web-site, Wikipedia, vision-therapy.com, OEPF publications.

34