Evaluation and Treatment of Visual Deficits Following Brain Injury

Deficits in Visual Acuity

In the normal eye, most deficiencies in visual acuity are due to defects in the optical system (the cornea or lens or even the length of the eyeball), which cause images to be focused poorly on the retina.¹⁰² The three most common optical defects that reduce acuity are myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. In myopia, the image of an object is focused at a point in front of the retina and is therefore blurred when it reaches the retina. Myopia is corrected by placing a concave lens in front of the eye. In hyperopia the image comes into focus behind the retina, which causes the image to remain out of focus on the retina. Hyperopia is corrected by placing a convex lens in front of the eye. Figure 24-6 illustrates these defects. In astigmatism, light is focused differently by two meridians 90 degrees apart. A cornea that is not perfectly spherical and smooth but is more spoon shaped or dimpled usually causes this defect. It results in blurring of the image because both meridians cannot be focused on the retina. Astigmatism is corrected by placing a cylindrical lens in front of the eye.

Visual acuity deficits primarily occur as a result of impairment in three areas of visual processing: disruption of the ability to focus light onto the retina, inability of the retina to accurately process the image, and inability of the optic nerve to transmit the information to the rest of the CNS for processing.¹⁰⁶ These impairments may be the direct result of a brain injury, a disease process, or a change in the eye occurring incidental to the injury. It is not possible to describe all of the conditions that can result in reduced acuity after brain injury, but the most common are described in the sections that follow.

Occupational Limitations Caused by Reduced Visual Acuity

Reduced visual acuity can cause limitations in a significant number of daily occupations. The severity of the limitation depends on the extent of the loss in acuity and whether there has been a loss of central acuity, peripheral acuity, or both. Loss of central acuity results in an inability to discriminate small visual details and to distinguish contrast and color. Activities dependent on reading, writing, and fine motor coordination (e.g., reading recipes and labels on foodstuffs, dialing a telephone, writing a check, paying a bill, applying makeup, shaving, identifying money, and shopping) will be affected. When peripheral acuity is reduced, as occurs with a VFD, mobility will be affected. The client may be unable to identify landmarks, see obstacles in the path of travel, or accurately detect motion, which may impair his or her ability to ambulate safely and maintain orientation in the environment. This may reduce independence in driving, shopping, and participation in community activities.

Assessment of Performance Skills

All assessment of performance skill begins with observation of the client’s performance in daily activities. Clients with deficits in visual acuity often complain of an inability to read print and may state that the print is too small or too faint to read. Complaints that print is distorted, that parts of words are missing, or that the words run together and swirl on the page are also common. Clients with deficits in CSF may complain of an inability to see faces clearly. These clients may also be unable to distinguish between colors of similar hue, such as navy blue and black, or to detect low-contrast substances such as water spilled on the floor.

If a decrease in visual acuity is suspected, a screening is completed to determine how the acuity has changed. To obtain a complete picture of the client’s visual acuity, both high- and low-contrast acuity are measured. High-contrast acuity is measured both for distance, using a test chart at a distance of 1 m or greater, and for reading, using a text card at 40 cm (16 inches). When measuring visual acuity, the practitioner must be sure that the chart is well illuminated and held at the specified distance from the client. Adequate illumination is important because as illumination decreases, so does acuity (no one can read a letter chart in the dark). Because acuity is depicted as a fraction of distance over letter size (e.g., 20/20 or 20/200), the measurement is not accurate unless the viewing distance is accurate. All test charts specify a distance at which they are to be used, and this should not be altered.

The client’s acuity level is determined by the smallest line of optotypes that can be read with good accuracy. The client is instructed to read the optotypes on the chart out loud, beginning with the largest line and continuing to lower lines until the print is too small to see. Clients with brain injury may have deficits in cognition, language, and perception that interfere with the ability to provide an accurate and timely response in a testing situation. Extra time may be needed for the client to locate the optotype, process the image, and respond. Slowness in responding therefore does not necessarily indicate that the client lacks the acuity to identify the optotype. If the client struggles with the identification of optotypes on each line but is accurate, the test should proceed until a line is reached on which the client can no longer accurately identify the majority of the optotypes.

The most useful chart for the OT practitioner is one that measures visual acuity as low as 20/1000 so that significant reductions in acuity can be measured. Standard charts measure visual acuity primarily in the range that can be compensated for with eyeglasses and measure nothing below 20/200 Snellen acuity. When acuity is below that level, the client is referred to a low-vision specialist for evaluation. Because some conditions such as optic nerve damage or macular diseases can result in profound vision loss (less than 20/400 acuity), it is important for a practitioner to be able to measure acuity in the lower ranges so that appropriate referral and modifications can be made. The LeaNumbers Low Vision Test Chart and the Warren Text Card from the biVABA are examples of test charts that measure visual acuity in the low-vision ranges.

CSF is also assessed by viewing optotypes printed on a chart that is held at a specified distance from the client. However, for this type of testing the optotypes (which may be letters, numbers, symbols, or sine wave gratings) remain the same size but diminish in contrast as one proceeds down or across the chart. The client is asked to identify as many optotypes as possible. There are many forms of CSF tests. The least expensive and most portable test charts are those designed by Dr. Lea Hyvarinen and include the Lea-Numbers Low Contrast Screener (part of the biVABA), the LeaSymbols Low Contrast Screener, and the LeaNumbers and LeaSymbols Low Contrast Tests. When CSF is measured, the client is asked to read down the chart as far as possible until the optotype is too faint to be identified. As with high-contrast acuity testing, the test chart must be held at a specific distance and must be well illuminated to obtain an accurate measurement.

In assessing visual acuity, the OT practitioner is not responsible for diagnosing the cause of the deficiency, but rather linking the presence of the deficiency to a limitation in occupational performance. This is a subtle but important distinction that affects the assessment procedure. When a client has reduced visual acuity, the ophthalmologist or optometrist uses the results of the assessment to determine the cause of the reduction (e.g., damage to the retina or cornea or the presence of a refractive error). With this information, the eye care specialist determines how to manage the condition to restore optimum sight with optical devices (glasses or contact lenses), a surgical procedure, or medication prescription. In contrast, when an OT practitioner determines that a client has reduced visual acuity, the information is used to modify activities and the environment so that the client can compensate for the loss and successfully complete daily activities. For example, if a client cannot read the size of print on a medication label, the OT practitioner determines whether the print can be enlarged to a size that the client can read or determines another way for the client to identify the medication bottle.

Intervention

If a significant reduction in visual acuity is noted, the client should be referred to an ophthalmologist or optometrist to determine the nature and cause of the visual loss and whether vision can be restored. Referring clients to specialists can take days, weeks, and even months to complete. The client’s intervention program cannot be placed on hold while the referral is being processed; therefore, the OT practitioner uses the information obtained from the assessment to modify the environment and activities and enable the client to use his or her remaining visual acuity. This is achieved by increasing the visibility of the environment and tasks through manipulation of physical context.

Visual Field Deficits

Damage to receptor cells in the retina or to the optic pathway that relays retinal information to the CNS for processing results in a VFD.^{3,54,80,106,129} Figure 24-1 illustrates this pathway as it changes from the optic nerve to the optic tract to the GCTs. The location and extent of the VFD depends on where the damage occurs on the pathway. Although any type of VFD is possible after brain injury, homonymous hemianopia resulting from a lesion along the GCTs is the most commonly occurring deficit.¹³⁴ Hemianopia (hemi = half, anopia = blindness) means that there has been loss of vision in half of the visual field in the eye. Homonymous means that the deficit is the same in both eyes. A lesion along the GCTs in the right hemisphere causes left homonymous hemianopia; a lesion along the GCTs in the left hemisphere causes right homonymous hemianopia. In stroke, most hemianopias are caused by occlusion of the posterior cerebral artery,^40,134 although a middle cerebral artery stroke such as that experienced by Penny in the case example can also cause this deficit.

Occupational Limitations Caused by Visual Field Deficits

Although a VFD is often considered a mild impairment in comparison to the dramatic loss of use of the limbs, it can create changes in visual processing that significantly limit daily performance.⁴⁰ The most important change occurs in the search pattern used by a person with a VFD to compensate for the blind portion of the visual field. Instead of spontaneously adopting a wider search strategy (turning the head farther to see around the blind field), the person tends to narrow the scope of scanning.^89,132 The person typically turns the head very little and limits visual search to areas immediately adjacent to the seeing side of the body. The reason for this odd strategy is the influence of a visual process known as perceptual completion.^{48,73,91,99,105} Perceptual completion is a process whereby the CNS samples a visual array and internally completes a visual scene based on an expectation of the visual information that would be found in the array, as illustrated in Figure 24-8. The perceptual outcome of this process is that the viewer perceives that he or she is seeing a complete visual scene, even though part of the visual information in the scene was not recorded.^55,105

Perceptual completion provides speed in information processing by enabling an individual to construct a complete visual scene based on partial visual input. Accordingly, it plays an important role in the person’s ability to adapt to fast-paced and dynamic environments. However, in the case of significant visual field loss, the presence of perceptual completion makes it difficult for the client to determine how his or her visual field has changed.^73,99 Because of perceptual completion, a client with a VFD is not immediately aware of the absence of vision after onset of the deficit.^71,73,105 He or she perceives the presence of a complete visual field without gaps or missing information. However, the CNS cannot place objects in a visual scene that it does not actually see. Therefore, the client may not be aware of unanticipated objects on the blind side. As a result, the client may run into a recently placed chair or other obstacles on the blind side or may not be able to find items placed within the blind field. Until the client becomes aware of the VFD, he or she will have the odd perception of a complete visual scene in which objects always seem to be appearing, disappearing, and reappearing, without warning, on the affected side. Uncertainty regarding the accuracy of visual input on the affected side causes the client to adopt a protective strategy in which he or she attends only to visual input from the intact visual field.^89,132 This creates a narrowed scope of scanning restricted to the midline of the body and seeing side. The restriction creates significant limitations in occupations that require monitoring of the entire visual field, such as driving a car or traversing a busy environment.

Even when the person becomes aware of the presence of a VFD, visual search into the blind field is often slow and delayed.^51,78,89,132 Again, the culprit is perceptual completion, which eliminates the presence of a marker to indicate the boundary between the seeing and nonseeing fields. Unable to determine the actual border of the seeing field or where a target might be within the nonseeing field, the client naturally slows down when scanning toward the blind field. The slow visual search toward the affected side increases the difficulty that the client has navigating and finding objects within the environment and also reduces reading speed.

If the hemianopia affects the macular portion of the visual field, especially the fovea, a client may miss or misidentify visual details when viewing objects because part of the object falls into the blind area of the field. This can create significant challenges in reading.^{13,18,29,30,32,68,69,114,133–135} Normal readers view words through a “window” or perceptual span that allows them to see approximately 18 characters (letters) with each fixation of the eye.¹³³ The reader typically moves from word to word by using a series of consecutive saccadic eye movements to cross the line of print. The presence of hemianopia can reduce the width of the perceptual span from 18 characters to as few as 3 to 4. This may cause the client to view only part of a word during fixation and even skip over small words, which often results in misidentification and omission of words.

For example, a client with left hemianopia may read the sentence “She should not shake the juice” as “He should make juice,” with “she” transformed into “he” and “shake” into “make” and leaving out “not” and “the.” Errors such as these cause the client to have to stop and reread sentences, thereby reducing reading speed and comprehension. Accuracy in reading numbers generally creates more challenge for the client than reading words does. Whereas context alerts the client to an error when reading sentences (the sentence does not make sense), numbers appear without precise context, which causes mistakes to go unnoticed. For example, a bill for $28.00 may be misread as $23.00 and the error missed until a notice of insufficient payment is received. Clients making these kinds of errors quickly lose confidence in their ability to pay bills and manage their checkbook and turn over these important daily occupations to someone else.

If the VFD has occurred on the same side as the dominant hand, the client may have difficulty visually guiding the hand in fine motor activities. The most common functional change is a reduction in writing legibility. The client often cannot visually locate and maintain fixation on the tip of the writing instrument as the hand moves into the blind visual field, which causes the handwriting to drift up and down on the line. Writing over something that was just written and improperly positioning handwriting on a form are also common mistakes. Quilting, hand sewing, pouring liquids, and other fine motor activities are likewise frequently impaired.

The changes described (narrow scope of scanning, slow scanning toward the blind side, missing or misidentified visual detail, and reduced visual monitoring of the hand) contribute to a variety of limitations in performance. The primary activities affected include mobility, reading, writing, and the daily occupations dependent on these skills. Such occupations include personal hygiene and grooming, medication management, financial management, meal preparation, clothing selection and care, meal preparation, home management, telephone use, and yard work. In general, the more dynamic the environment where the occupation is completed and the wider the field of view required to perform the task, the greater the limitation. Therefore, only minor limitations are generally experienced in basic ADLs, as opposed to significant limitations in shopping and driving.

Persons with a VFD commonly face significant emotional challenges in adapting to this considerable visual loss. For example, clients with a VFD regularly report feeling a sense of anxiety when moving in unfamiliar environments. Sometimes the anxiety can be so severe that clients experience an autonomic nervous system reaction in which they become nauseated and short of breath and break out into a sweat in crowded environments. One individual with a VFD described this sensation as “crowditis” and reported that he became physically ill if he had to go into a department store or other crowded environment. This anxiety can become debilitating and lead to withdrawal from community activities and social isolation. Other clients report a tremendous loss of self-confidence because of the numerous mistakes that they make during the course of a day, and many state that they experience depression because of their limitations, especially in the ability to drive a car and read accurately.

Assessment

The process of measuring the visual field is known as peri-metry.³ Several types of perimeters are available. They range from simple bedside assessments (such as the confrontation test), which give a gross indication of field loss, to the very precise imaging of a scanning laser ophthalmoscope (SLO).^{3,46,102,105,116} The perimetry test selected depends on the availability and cost of the test and the ability of the client to participate in testing. For example, confrontation testing does not incur any expense and can be performed nearly anywhere, whereas imaging with an SLO must be completed by a specially trained technician in a center that has purchased the $120,000 instrument. In between these two extremes are the tangent screen, Damato Campimeter, manual bowl perimeters (the Goldmann), and automated bowl perimeters (the Humphrey), ranging in cost from $100 to $20,000. In general, the more expensive the apparatus, the more precise the measurement provided.

All perimetry testing involves three parameters: fixation on a central target by the client while the testing is performed, presentation of a target of a specific size and luminosity in a designated area of the visual field, and acknowledgment of the second target without breaking fixation on the central target.³ Testing is done with either static or kinetic presentation of the target. In static presentation, the target appears in a specified area of the visual field without being shown moving to that location. In kinetic testing the target moves in from the periphery until it is identified.^3,102

The most accurate perimetry test available to clinicians is computerized, automated perimetry, which is completed by either an ophthalmologist or optometrist.³ During automated perimetry, the client places his or her chin on a chin rest and fixates on a central target inside a bowl-shaped device. As the person fixates on the central target, lights are displayed inside the bowl in varying locations and intensities. The client responds to each seen light by pushing a small button. The test can be very thorough, with lights presented in more than a hundred locations within the field and the intensity of the light increased in a step threshold sequence if the target is not appreciated the first time. The result is an accurate measurement of the areas of absolute loss (no response) and relative loss (decreased retinal sensitivity) within the field. An ophthalmologist or optometrist may also use a simpler screening test, the tangent screen, to assess the integrity of the central visual field. The tangent screen consists of a black felt screen with a grid stitched into the felt in black thread so that the grid is visible only to the examiner.³ The client sits directly in front of the screen at a distance of 1 m. The client is instructed to fixate on the center of the screen as the examiner moves or places a white target attached to a black wand in a certain area of the screen. Without breaking fixation on the center of the screen, the client indicates when the target is seen. If the client does not see the target when it is presented, that point in the visual field is recorded as a loss. The examiner uses the grid to determine the location of the field deficit.

OT practitioners can screen for a VFD by using simple perimetry testing in combination with careful observation of client performance of daily occupations. Confrontation testing is a bedside examination that provides a crude indication of visual field loss.^102,116 To complete a static confrontation test, the examiner sits in front of the client at a meter distance and has the client fixate on a centrally placed target (the examiner’s eye). The examiner then holds up two targets in each of the four quadrants of the visual field (right upper, right lower, left upper, and left lower). The client indicates whether the targets are seen.^57,102,106 For a kinetic test the examiner stands behind the client and moves a target (generally a penlight) in from the periphery while the client fixates on a central target. The client indicates as soon as the target is noticed. Standardized versions of these tests are included in the biVABA. Because confrontation testing has been shown to be unreliable in detecting all but gross defects, OT practitioners using this form of testing must be careful to correlate their findings with observations of client performance.¹¹⁶ If the confrontation test shows no deficit but clinical observations suggest that a deficit is present, the clinical observations should carry the greater weight in deciding whether a deficit exists.

Assessment using perimetry devices such as the Damato 30-Point Multifixation Campimeter (biVABA) enables OT practitioners to obtain a more accurate measurement of central visual field function. The Damato Campimeter, shown in Figure 24-9, is a portable test card that provides a precise measurement of the central 30 degrees of the visual field. The test grid consists of 30 numbered targets that place the test stimulus at known points in the visual field by moving the eye rather than the target. The test stimulus is a 6-mm black circle that is shown in the center part of the card. The client is instructed to fixate on one of the numbered targets. The test stimulus is then shown in the central window, and the client indicates whether the circle is seen. If the client does not see the black circle, that point in the visual field is recorded as a loss. The test proceeds with the client successively moving the eye to view the numbered targets until the entire field is mapped out.

Clinical observation of the client’s behavior is especially important to confirm the presence of a VFD because of the limitations of perimetry testing.¹⁰² Clients with fluctuating or limited attention, language, and cognition may give unreliable perimetry results. It may also be difficult to distinguish between a VFD and a deficit in visual attention. However, the client’s performance of daily activities will strongly indicate the presence of a VFD. For example, the presence of a VFD may be indicated if any of the following are observed: the client changes head position when asked to view objects placed in a certain plane, the client consistently bumps into objects on one side, the client misplaces objects in one field, or the client makes consistent errors in reading.

Perimetry tests establish only whether a VFD is present and the size and location of the deficit. To determine whether intervention is needed, the practitioner must determine whether the client is able to compensate for the VFD in performing daily activities, as well as the quality and consistency of that compensation. The presence of a VFD can cause significant limitations in daily occupations. The level of impairment will depend on whether the VFD occurs alone or in conjunction with visual inattention. An analysis of occupational performance should be completed to identify limitations in basic and instrumental ADLs. If the client demonstrates difficulty completing an activity, the visual requirements of the activity should be analyzed to determine whether the VFD is interfering with performance. For example, if the client is unable to locate a toothbrush during grooming, is it because the toothbrush is stored on the side of the client’s field deficit?

Reading is another daily activity often affected by a VFD. The Visual Skills for Reading Test (VSRT) provides an effective way to measure interference of the VFD in reading performance. The VSRT is designed to assess the influence of a scotoma (or field loss) in the macula on the visual components of reading, including visual word recognition and control of eye movement.¹²⁴ The client is asked to read single letters and words printed on a card. Three different versions of the test card in four font sizes are included in the test to accommodate clients with low vision and to permit retesting. The words are not in context and are designed so that they can be misread and still make sense (e.g., “shot” can be mistakenly read as “hot”). The test measures reading accuracy and corrected reading rate and provides information on the prevalent types of reading errors made by the client. The client’s performance on the letter and reading charts used to measure visual acuity may also indicate the influence of a VFD on reading performance. Because of the wider visual field, a client with a VFD may have more difficulty reading the larger symbols and words on the chart and may be able to read faster and more accurately as the optotypes (and field) decrease in size. Telephone Number Copy, part of the biVABA, provides information about the client’s accuracy in reading numbers. In this test the client is required to copy down telephone numbers that include numbers easily misread by persons with a VFD, such as 6, 8, 9, and 3.

To effectively compensate for the VFD, the client must execute an organized and thorough search of the blind field by using the seeing portion of the visual field. This means that a client with a left VFD must use the right visual field to search both the left and right fields. Clients with a VFD demonstrate difficulty searching both peripersonal space (the space immediately around the body) and extrapersonal space (the space extending from the body into the environment). Deficiencies in searching the peripersonal space affect the performance of basic ADLs such as grooming, dressing, reading, and writing, as well as instrumental ADLs requiring monitoring of a wider visual field, such as meal preparation or leisure activities. Deficiencies in searching the extrapersonal space have a pronounced impact on mobility and affect activities in outside and community environments, such as driving, shopping, and mowing the yard.

To navigate dynamic community environments, the client must use a wide scanning strategy that is initiated on the side of the deficit and executed quickly and efficiently. The client must also be able to shift attention and search rapidly between the central visual field and the peripheral visual field. A variety of observational tests can be used to measure the ability to compensate for the VFD during mobility. An objective assessment of the client’s ability to execute compensatory search strategies can be made with the Dynavision 2000, an apparatus increasingly used in rehabilitation to assess and train visual motor performance (Figure 24-10).^63–66 OT practitioners without access to a Dynavision can use a laser pointer to observe the client’s search capability. The beam of light from the pointer is projected onto various areas of a blank white wall, and the client is instructed to locate and touch the projected red dot. The strategy used by the client to locate the dot and the efficiency of the strategy are noted. Integration of visual scanning with ambulation is the final component of the mobility assessment and must be completed to determine whether the client will be able to compensate for the deficit during body movement. This can be assessed by using tests such as the ScanCourse from the biVABA. To complete a ScanCourse, the client is instructed to walk through a course and identify targets placed in various locations on the left and right sides. The client’s ability to locate the targets on each side during ambulation is noted.

Intervention

The performance limitations experienced by persons with a VFD generally fall into two categories: difficulty with mobility and difficulty with reading. Because of the mobility limitation, clients will experience limitations in daily occupations that must be performed in dynamic environments, such as shopping and participating in community events. Resumption of driving may or may not be a goal, depending on the driving statutes of the state in which the client resides. Some states do not specify a minimum degree of visual field for licensure. In these states a client may be able to safely resume driving if given the proper training. Challenges in reading will cause difficulty completing such activities as financial management and meal preparation.

Although a limited body of research shows that some restitution of the visual field may be possible with intensive rehabilitation,^7,58,59,86 return of visual field function is unlikely.¹⁰⁶ Therefore, the major focus of intervention is to improve compensation for the visual field loss. Compensation for the VFD requires adopting a conscious, cognitive strategy of using head movement to search and broaden the visual field. Because the CNS exercises perceptual completion, the client often lacks insight into the extent and boundaries of the field deficit. Successful compensation requires the client to firmly believe that the deficit exists and that the visual input from the blind side cannot be trusted. A client able to develop this level of insight will usually learn to effectively compensate for the deficit. Every effort must be made through activities and educational materials to make the client aware of the location and extent of the deficit.

Deficits in Visual Attention and Scanning

Studies have shown that disruption of the normal visual search strategy can occur after brain injury. The characteristics of the disruption vary, depending on which hemisphere was damaged. Visual search deficits associated with right hemisphere injury are characterized by avoidance in searching the left half of the visual space.^{10,22,24,37,38,45,47,90} This condition is known as hemi-inattention. Instead of initiating the normal left-to-right visual search pattern, clients with right hemisphere injuries often begin and confine the search to the right side of a visual array. This creates an asymmetric search pattern instead of the normal symmetric pattern. The client misses visual information on the left side and, as a result, may be deprived of the information needed to make accurate identification and decisions.

Hemi-inattention is associated with injuries to the right hemisphere and probably occurs because of a difference in the way that the hemispheres are programmed to direct visual attention.^47,107 As illustrated in Figure 24-12, the left hemisphere directs attention toward the right half of the visual space surrounding the body. In contrast, the right hemisphere directs visual attention toward both the right and left halves of the space surrounding the body. If a lesion occurs in the left hemisphere, visual attention and search toward the right side are diminished, but some attentional capability is still provided by the right hemisphere. A similar lesion in the right hemisphere may completely eliminate attentional capability toward the left because there is no other area directing attention toward the left side.

Hemi-inattention is often confused with the presence of a left VFD in the client. Although both conditions may cause the client to miss visual information on the left side, they are distinctly different conditions and do not have the same effect on performance. When a left VFD occurs, the client attempts to compensate for the loss of vision by engaging visual attention.^10,11,51,75 The client directs eye movements toward the blind left side in an attempt to gather visual information from that side. Because of the field deficit, however, the client may not move the eyes far enough to acquire the needed visual information from the left side and as a result may appear inattentive. In contrast, a client with hemi-inattention has lost the attentional mechanisms in the CNS that drive the search for visual information on the left. No attempt will be made by the inattentive client to search for information on the left side of the visual space, and no eye movement or head turns will be observed toward the left side.^22,51 The most significant change in visual search takes place when the two conditions occur together in a client.^10,20 In this case the client is not receiving visual input from the left side because of a VFD and does not compensate for the loss of visual input by directing attention toward the left side. The combination of hemi-inattention and left VFD creates severe inattention, often called visual neglect. Clients with this condition show exaggerated inattention toward the left half of the visual space surrounding the body and often do not move the eyes past midline toward the left or turn the head toward the left side. Visual neglect may be compounded by neglect of the limbs on the left side of the body or neglect of auditory input from the left side.^45,61 The presence of neglect is consistently associated with poor rehabilitation outcomes.⁵¹

Another change in visual search associated with right hemisphere lesions is a tendency to fixate first on the most peripheral visual stimuli occurring in the right visual field.⁴⁵ If two visual stimuli simultaneously appear in the right visual field, the client will attend first to the most peripheral stimulus.³¹ A client with this tendency makes frequent head turns to attend to events occurring in the right peripheral field, thus giving the impression of being distractible. Yet another change in visual search is a reluctance to rescan for additional information once an area has been viewed, especially if the area is on the left side.⁹⁰ This may cause the client to miss certain visual details when viewing complex visual arrays.

Although several distinct changes in visual search have been observed with right hemisphere lesions, only one has been observed following left hemisphere lesions. Clients with left hemisphere injury may show a symmetric decrease in searching for detail when viewing a visual array.^15,45,117 These clients symmetrically scan the visual array for information but do not examine specific aspects of the visual scene to gather additional information. Consequently, they may miss visual details and often cannot accurately interpret or identify the objects around them. Left hemisphere injury does not result in hemi-inattention or neglect.

In general, clients with injuries to either hemisphere are slower in scanning and show more erratic fixation patterns than do persons without brain injury.^74,126 They also have greater difficulty engaging selective attention and executing an organized and efficient visual search strategy. Research has shown that when persons with brain injuries are asked to search complex visual arrays for specific targets, they have difficulty maintaining attention on the salient features of the target and mistakenly select targets with similar features.^93,126 They also demonstrate an inability to superimpose an organized, efficient structure for visual scanning when asked to search an array of randomly displayed objects. For example, if asked to locate a certain individual seated among others on rows of benches (a structured visual array), the injured person would be able to accomplish the task. However, if asked to find the same individual standing in a jumbled crowd of persons (a random visual array), the injured person would display a random approach to searching the array and would probably miss the target.

Occupational Limitations Caused by Visual Inattention

Disruption of visual attention creates asymmetry and gaps in the visual information gathered through visual search. The quality of an individual’s adaptation to the environment decreases because the CNS is not receiving complete visual information in an organized fashion and is therefore unable to effectively use this information to make appropriate decisions. A reduction in visual attention will affect all aspects of the performance of daily occupations. However, the most affected activities will be those that require inspection and integration of significant amounts of visual detail and those completed in dynamic environments. Driving and reading are two diverse examples of tasks often significantly affected by inattention.

Because visual attention is modulated through an extensive neural network involving the entire CNS, some capacity for visual attention is generally retained even in individuals with severe brain trauma.⁸¹ Conversely, because so many neural structures contribute to attention, changes in visual attention occur even with mild injuries.⁹⁹ Whether a change in visual attention affects occupational performance depends on the task to be completed. Tasks such as reading can require enormous amounts of selective visual attention if an individual is reading a highly technical textbook and less selective attention if the individual is reading an advertisement. The task of driving requires continuous global attention to monitor the speed and position of other vehicles and objects and sporadic selective attention to landmarks, street signs, and traffic lights. Whether a deficiency in visual attention occurs after brain injury depends on the circumstances and requirements of the tasks that the client completes.

Assessment

As a process found at the intermediate level of the visual perceptual hierarchy, visual attention can be affected by deficits in lower-level visual functions (visual acuity, oculomotor function, and visual field). Therefore, these functions should be assessed before visual attention is measured. The presence of aphasia and motor impairment can also affect performance on assessments for visual attention. How efficiently and completely a person attends to and takes in visual information determines the ability to use the information for adaptation. Therefore, the emphasis in assessment is on observing how a client initiates and carries out visual scanning to complete a task requiring visual search. During the assessment the OT practitioner should answer the following questions: Does the client initiate an organized search strategy? Can the client carry out the search strategy in an organized and efficient manner? Does the client obtain complete visual information from a visual search? Is the client able to identify visual detail correctly? Does the client’s ability to search for information decrease as the visual complexity of the task increases?

Research has shown that persons with good visual attention demonstrate specific characteristics of search patterns that make them effective in obtaining visual information.^48,122,131 These characteristics include strategies that are organized, symmetric, thorough, resilient, and consistent. Use of these strategies generally results in good accuracy and speed in completion of visual search tasks. In contrast, persons with a significant VFD or inattention often have ineffective search strategies. These individuals demonstrate incomplete or abbreviated patterns in which only a portion of the visual array is searched, usually in a random, unpredictable fashion.^{15,23,37,48,51,74,78,93,126} The organization and accuracy of the pattern often break down when the person is challenged to search more complex visual arrays. Figure 24-13 provides examples of some of the ineffective search strategies used on the visual search subtests of the biVABA by persons with brain injury. A client using ineffective search strategies may not acquire sufficient visual information to complete perceptual processing accurately. The client may acquire the information in such a way that it cannot be used to complete perceptual processing, or the person may not acquire the information rapidly enough to enable adaptation. The subsequent disruption of perceptual processing may cause errors in decision making and adversely affect performance of a variety of ADLs.

When measuring visual attention, the OT practitioner must be aware that visual search can be significantly affected by the presence of both a VFD and hemi-inattention. Because a VFD and hemi-inattention are not the same condition, it is necessary to distinguish between the two to establish an effective intervention plan. This can be difficult, both because similar errors are observed with the two conditions on search tasks and because the two can also occur together in the same client. However, differentiation can be accomplished by observing the strategies used by the client to complete visual search tasks such as those on the biVABA (Figure 24-13). Although both VFDs and hemi-inattention can result in decreased accuracy in identifying targets on a visual search task, the characteristics of the search deficiencies are different.^{10,22,27,28,41,51}

For example, a client with left hemianopia may demonstrate a left-to-right linear search pattern that is abbreviated on the blind side. The search pattern is organized but results in a number of errors on the left because the client did not see that side of the array. In contrast, a client with hemi-inattention may demonstrate an asymmetric pattern in which visual search is initiated and confined to the right side with a disorganized and random search pattern. The pattern also results in a large number of errors on the left. Although accuracy in the search task may be similar for these two clients, the cause of the errors is different. By observing the strategy used by the client to complete the search task, it is possible to distinguish between the two conditions. Table 24-2 compares the characteristics of search patterns used by persons with hemianopia and those with hemi-inattention. When the two conditions occur together, it is important to determine the severity of the inattention because this will determine whether the client is able to learn the strategies needed to compensate for the VFD.

The visual search tests that have been described are pencil-and-paper tasks presented in a restricted and well-defined personal space. Determining how the client applies a search strategy to the broader extrapersonal space requires the use of a test such as the ScanBoard described by Warren.¹²² The test, part of the biVABA, consists of a large (20 by 30 inch) board with a series of 10 numbers displayed in an unstructured pattern. The board is placed at eye level and centered at the client’s midline. The client is asked to scan the board and point out all of the numbers that he or she sees. The examiner records the pattern that the client follows in identifying the numbers. Research using this test has shown that adults with normal visual search use an organized, sequential search pattern, beginning on the left side of the board and proceeding in either a clockwise or counterclockwise fashion until all of the numbers are identified. In contrast, adults with deficits in visual attention demonstrate disorganized, random, and often abbreviated search strategies, with numbers frequently being missed on one side of the board. Those with hemi-inattention often show an asymmetric pattern, with visual search initiated and confined to the right side of the board. Clients with a VFD may miss numbers on the blind side but demonstrate an organized search strategy.

Intervention

Information gathered from observing the client complete visual search tests should reveal specific deficiencies in the scanning pattern that the client uses to acquire visual information during the performance of daily tasks. For example, it may be observed that the client does not search toward the left side of visual arrays. If this deficiency is significant, similar performance should be observed when the client completes a daily activity. This could be an inability to locate items placed on the left side of the sink while grooming or a tendency to begin reading a recipe in the middle of the line of print instead of at the left margin.

Depending on the severity of the deficit, some clients with inattention are able to complete basic and habitual daily activities and experience difficulty only with tasks that are unfamiliar or require search of a complex visual array.⁷⁶ Others, especially those with neglect, may have difficulty with such a simple task as finding all the food on their plate. By combining information from visual search tests with that gained from observation while performing ADLs, it is possible to determine whether and how the client’s performance of daily activities has been affected by the impairment in visual search. The goals on the intervention plan should be worded to reflect the specific daily activities compromised by the inattention. For example, the intervention plan could include such goals as “The client will be able to complete grooming independently” or “The client will be able to prepare a simple meal independently.”

The goals established for independent performance of ADLs are achieved by ensuring that the client learns to take in visual information in a consistent, systematic, and organized manner. Before clients can learn to reorganize a visual search, they must understand how their visual search and attention have changed. To facilitate development of this insight, the OT practitioner should carefully review the results of the client’s performance on the visual search tests and show the client how his or her search pattern differed from the norm and caused errors. If after receiving this feedback the client wishes to retake one of the tests, he or she should be allowed to do so. If the client’s performance improves on the retest, this is an indication of the capability of benefiting from therapy intervention and serves as a justification for intervention. Likewise, if the client’s performance does not improve, this helps verify the significance of the deficit and also may indicate reduced rehabilitation potential.

The intervention plan should incorporate compensatory strategies and environmental modification. The primary compensatory strategy taught to a client with hemi-inattention is to reorganize the scanning pattern to begin visual search on the left side of a visual array and progress from left to right.^{5,28,88,125,127} Use of this pattern will counteract the client’s tendency to restrict all visual search to the right side and will increase the symmetry of the search pattern. Clients with left hemisphere injuries do not demonstrate asymmetry in visual search but often fail to notice details when searching visual arrays. These clients should be taught to initiate careful item-by-item search of visual arrays. Two scanning strategies are taught to all clients: a left-to-right linear pattern for reading and inspection of small visual detail and a left-to-right clockwise or counterclockwise pattern for viewing unstructured and extra-personal visual arrays.⁴ Activities should be selected that encourage and reinforce the use of these patterns.

Compensatory strategies can be taught more effectively if intervention activities are designed in accordance with the following guidelines:

Insight on the part of the client into the nature of the visual deficit and how it has affected functional performance is critical to learning compensation.^110–112 According to Toglia,¹¹³ one of the reasons that clients with brain injury do not spontaneously recognize their limitations and the need to compensate is that their concept of their capabilities is based on premorbid experiences. This causes these clients to overestimate their abilities after injury. Without a realistic understanding of limitations, the client may be unwilling to use compensatory strategies. To increase insight, Abreu and Toglia¹ advocate teaching a client to monitor and control his or her performance by learning to recognize and correct for errors in performance. Giving the client immediate feedback about the performance and pointing out deficiencies facilitate this process of error detection. The process can also be facilitated by teaching the client to use self-monitoring techniques such as activity prediction, in which the client predicts how successfully an activity will be performed and identifies the aspects of the activity in which errors are likely to occur. The client then compares actual performance with predicted performance. This technique helps the client develop anticipatory skills and increase awareness of how the deficit affects functional capabilities. The use of video feedback has also been shown to be useful in enabling clients to understand how their neglect behavior affects occupational performance.¹¹²

Some clients, because of the severity of their deficits, lack the cognition to benefit from training in compensatory strategies. Although treatment intervention is limited, such clients may benefit from a modification of the environment to help the client use his or her limited attentional capabilities. The environment can be made more visible and “user-friendly” by reducing factors that place stress on visual processing. Suggested environmental modifications include the following:

Deficits in Oculomotor Function

Deficits in oculomotor control following brain injury generally result from either of two types of disruption: specific cranial nerve lesions causing paresis or paralysis of one or more of the extraocular muscles that control eye movements or disruption of central neural control of the extraocular muscles affecting the coordination of eye movements.^{5,60,72,74,96,97} In the first case, the message to the extraocular muscles through the cranial nerve is blocked; in the second case, the message comes through but is scrambled. In both cases, the functional results are decreased speed, control, and coordination of eye movements. Three pairs of cranial nerves control the extraocular muscles: the oculomotor nerve (III), the trochlear nerve (IV), and the abducens nerve (VI). Among them, these nerves are responsible for controlling seven pairs of striated muscles that surround and attach to the two eyeballs.

When a cranial nerve lesion is sustained, the muscles controlled by that cranial nerve are weakened or paralyzed, a condition known as paralytic strabismus.^82,119 As a result, the eye is unable to move in the direction of the paretic muscles and may even be unable to maintain a central position in the eye socket (i.e., it drifts in or out). Because the eyes must always move in synergy and line up evenly to maintain a single visual image, an individual sees a double image when the movement of one eye is impeded or when the eye’s position changes and does not match that of the other. This condition, diplopia or double vision, is the primary functional disruption observed in individuals with cranial nerve lesions.^82,119

Occupational Limitations Caused by Oculomotor Deficits

The presence of diplopia creates perceptual distortion, which may affect eye-hand coordination, postural control, and binocular use of the eyes. The limitations in performance experienced by the client depend on where the diplopia occurs within the focal range (the range in which a person can keep objects in focus). Diplopia occurring within 20 inches of the face will disrupt reading and activities requiring eye-hand coordination, such as pouring liquids, writing, and grooming. Diplopia occurring at a distance (greater than 4 feet) will affect walking, driving, television viewing, and playing sports such as golf and tennis.

To eliminate the double image, the client will often assume a head position that avoids the field of action of the paretic muscle.^8,72,119 For example, a client with a left lateral rectus palsy (cranial nerve VI) will turn the head toward the left to avoid the need to abduct the eye. A client with paralysis of the right superior oblique muscle (cranial nerve IV) will tilt the head to the right and downward to avoid the action of that muscle.⁸ Unless oculomotor function is carefully assessed, these alterations in head position may be interpreted as resulting from changes in muscle tone in the neck rather than as a functional adaptation purposely assumed to stabilize vision.

Often it is not the cranial nerves that are damaged during brain injury but the neural centers that coordinate their actions. These structures are scattered throughout the brainstem and communicate extensively with cortical, cerebellar, and subcortical areas of the CNS and the spinal cord.^52,77 In cases of traumatic brain injury, diffuse damage may take place throughout the brainstem and affect these control centers. If the centers are damaged, the person will have difficulty executing eye movements even though the cranial nerves are intact.^72,96,97,107 Disconjugate eye movements may occur and cause the client to have difficulty using the eyes together in a coordinated fashion. Dysmetric eye movement, in which the eye undershoots or overshoots a target, may also be observed.¹⁰⁶

Damage to the pretectal nuclei in the brainstem can cause convergence insufficiency, a condition in which the client is unable to obtain or sustain convergence of the eyes.^25,72 Convergence is the muscle action of moving the eyes inward in adduction. It is one of the three components of accommodation, the process that keeps objects in focus as they come into close view. When convergence insufficiency occurs, clients have difficulty obtaining or sustaining adequate focus during near-vision tasks (tasks within 20 inches of the face). Clients with this condition often complain of fatigue, eye pain, or headache after a period of sustained viewing in near tasks such as reading. As the eye muscles fatigue from the exertion of sustaining convergence during reading, clients may begin to complain that the print is swirling and moving on the page. The condition is frequently overlooked in evaluation because cranial nerve function is usually intact and clients’ complaints are instead attributed to inattention, lack of effort, or dyslexia.^25,72

These disturbances in ocular motility can create a variety of functional deficits for the client.^72,84 The speed and range of eye movement may be diminished. This will reduce the speed at which the client is able to scan the environment and take in visual information, thereby causing delays in responding to the environment. The client may have difficulty maintaining a clear image and may experience doubling and blurring of visual images.^53,72 There may be difficulty focusing at different distances from the body. Depth perception may be diminished. These conditions will create significant visual stress for the client and reduce concentration and endurance for activities. The client may respond to this increased stress by becoming agitated and uncooperative in therapy sessions or by complaining of headaches, eyestrain, or neck strain.

Because a number of factors can disrupt the control of eye movements, much skill and expertise are needed to accurately diagnose the oculomotor deficit and design an appropriate treatment intervention. Practitioners who treat this type of dysfunction should do so under the guidance of an optometrist or ophthalmologist who specializes in visual impairment caused by neurologic conditions.^39,84

Assessment

The purpose of an assessment completed by the OT practitioner is to determine whether the client is experiencing limitations in daily occupations because of dysfunction within the oculomotor system. It is not to determine whether the oculomotor dysfunction is the result of a cranial nerve lesion, brainstem injury, or other conditions. Determining the etiology of the dysfunction is the responsibility of the ophthalmologist or optometrist. However, the OT practitioner is often one of the first members of the rehabilitation team to observe that the client may have an oculomotor impairment affecting occupational performance. This frequently places the OT practitioner in the position of requesting further evaluation by an eye care specialist. To make an appropriate referral, it is necessary to perform a screening to identify patterns of oculomotor dysfunction that may account for the functional limitations observed in the client.

In assessing the client, a “listen and look” approach is used wherein the practitioner listens to the complaints being voiced by the client or the rehabilitation staff working with the client and looks for deviations in oculomotor control that may be contributing to these complaints. This approach is described in the biVABA, and the following steps in evaluation are from that assessment.

The first step in assessment is to obtain a visual history from the client. The history is necessary because adults with childhood histories of oculomotor dysfunction or reduced acuity often display oculomotor abnormalities that do not affect functional performance. These individuals frequently wear eyeglasses to correct for the deficiencies; in this case the eyeglasses must be worn during the assessment to obtain accurate results. Areas addressed in this part of the evaluation include whether the client had good vision before the brain injury, whether the client wears eyeglasses, and whether the client has a history of conditions that may affect oculomotor control, such as congenital strabismus, lazy eye, or amblyopia.

Next, the client is asked whether he or she is experiencing diplopia. If the response is affirmative, the client should be questioned about the characteristics of the diplopia. Does the diplopia disappear when one eye is closed? This indicates impairment of the extraocular muscles. Do objects double side to side or on top of one another? Is the diplopia present at near distances or at far distances? Is there any area within the range of focus at which the client is able to achieve single vision? The answers to these questions may suggest which cranial nerve has been injured (Table 24-3) and can also supply important information about limitations that the client may experience in daily activities. The OT practitioner concludes the interview by identifying activities that the client has difficulty performing that could be caused by oculomotor dysfunction. The practitioner should look for a pattern in the client’s response, such as difficulty with activities that require sustained focus in near space (reading, writing, and quilting). The practitioner should pay attention to whether the client’s visual difficulty seems to change with the focal length of the task and whether the client’s fatigue and reduced concentration appear to be related to activities requiring sustained focusing.

The next part of the assessment is observing the client’s eyes and eye movements for deficiencies. First, the eyes are evaluated for asymmetries in pupil size, eyelid function, and eye position as the client focuses on a distant object. Asymmetries such as a dilated pupil in one eye or a droopy eyelid (ptosis) may indicate cranial nerve involvement and suggest difficulty adjusting to light (light sensitivity) and reading. Next, movement of the eyes is observed by asking the client to track a moving object (such as a penlight) through the nine cardinal directions of gaze plus convergence.⁸⁷ This test can be thought of as an active range-of-motion test of the eyes because the nine cardinal directions represent the directions through which the eyes move. The test is used to determine whether there are deviations in strength and function of the extraocular muscles and is completed by observing the eyes move in a binocular test.

During the test, the OT practitioner observes the following: (1) symmetry of eye movement, (2) whether the eyes move the same distance in each direction, (3) whether the eyes are able to stay on target with a minimum of jerking movements, and (4) whether the client is able to hold the eyes in a deviated position at the end of the range for 2 to 3 seconds. Restriction of eye movement in a specific direction or difficulty moving the eyes in a specific direction may indicate impaired oculomotor function.⁸² Observing the eyes as they track an object moving toward the bridge of the nose tests convergence. Most adults can maintain focus and track an object to a distance of approximately 3 inches from the bridge of the nose. At that point one eye usually breaks fixation and moves outward. The point at which convergence is broken is known as the near point of convergence.⁸²

Although the near point of convergence is 2 to 3 inches from the bridge of the nose, few adults ever view objects that closely. Therefore, limitations in convergence are not generally functionally significant unless the client is unable to converge the eyes and easily maintain convergence to a distance of 12 to 16 inches from the bridge of the nose. An inability to converge the eyes to this distance and maintain convergence for several seconds while focusing on an object may cause the client to have difficulty performing tasks in near vision that require sustained focus. Observation of convergence insufficiency may explain complaints made by the client regarding such tasks as reading, writing, quilting, or sewing.

The final component of the assessment is diplopia testing, which is completed only if the client is complaining of diplopia.¹⁰⁶ Diplopia testing is used to determine the severity of the diplopia and whether it is caused by a “tropia” or a “phoria.” Tropia is the suffix applied when there is a noticeable deviation of the position of one eye in relation to the other when the client is viewing an object.^106,119 Phoria is the suffix used when there is a deviation of the eye that is held in check by fusion and is therefore not noticeable when the client is focusing on an object. These terms are used in conjunction with a prefix describing the direction of the deviation. Four prefixes are used: “eso,” meaning turning in of the eye; “exo,” turning out of the eye; “hypo,” turning downward of the eye; and “hyper,” turning upward of the eye. Esotropia therefore describes an observable, inward deviation of the eye commonly described as “crossed eyes,” whereas esophoria indicates that the eye drifts inward when the client is not focusing on an object but is held in check when the client is focusing on an object.⁷²

Diplopia testing is based on the principle that when an eye is required to fixate on an object, it will do so with the fovea. If an eye that is not fixating on a target is suddenly required to foveate, it will achieve foveation by making a saccade toward the target. By requiring the client to fixate with both eyes on a target and then covering one of the client’s eyes during fixation, the examiner can determine whether both eyes are aligned in focusing on the target and, if not, which eye is the deviant (strabismic) one.^87,118 Two tests are used: a cover/uncover test, which is completed when a tropia is suspected, and a cross or alternate-cover test, which is completed when a phoria is suspected.^87,118 If both eyes are aligned equally and fixating on the target, no movement of either eye will be observed when one is covered. If the eyes are not aligned, the deviating eye will move to take up fixation when the nonaffected eye is covered. Clients with tropias generally complain of constant diplopia when viewing objects and must have one eye occluded to eliminate the diplopia. Clients with phorias often complain of diplopia only intermittently, usually when fatigued or stressed by sustained viewing of a target. Although a phoric client may complete most activities without diplopia, he or she may experience significant visual stress, which can be manifested as headaches, eye strain, or decreased concentration.

The information gathered from the assessment should be compared with the client’s visual complaints and observations of his or her occupational performance to determine whether the oculomotor dysfunction is contributing to the client’s functional limitations. For example, the presence of convergence insufficiency may help explain the difficulty that the client is having in maintaining concentration when reading. As another example, the observation of downward movement of the left eye during the cover/uncover test may explain why the client complains of feeling off balance and unsure when descending stairs. If oculomotor deficiencies are observed that appear to limit occupational performance, referral should be made to an ophthalmologist or optometrist for further evaluation to determine the cause of the deficiency, the prognosis for improvement, and treatment options.

Intervention

The presence of oculomotor dysfunction does not usually prevent the completion of daily occupations; however, it does make completion of daily activities both tedious and fatiguing. The client may express reluctance to perform some activities or even stop performing them because of the constant visual stress. Motor and postural control may also be compromised and consequently reduce safety when navigating the environment. For these reasons, oculomotor dysfunction must be addressed during intervention, although it is not specifically identified as a goal on the intervention plan. That is, the goal remains a functional one such as safe and accurate completion of meal preparation, shopping, or bill paying, and management of the oculomotor dysfunction becomes one of the methods used to achieve the goal.

Intervention can be divided into four types: occlusion, application of a prism, eye exercises, and surgery.^{12,19,108,119} The last three interventions are used to re-establish fusion and binocularity and are performed only by ophthalmologists or optometrists. OT practitioners, under the direction of a physician, may apply occlusion. Most oculomotor dysfunction clears up without intervention within 6 to 12 months after the brain injury.^97,119 Accordingly, ophthalmologists do not generally believe that it is necessary to provide any intervention other than eliminate the diplopia for the client’s comfort during the recuperation period. If the diplopia persists and becomes chronic, surgery can be used to re-establish fusion. Optometrists often choose a remediation approach and prescribe eye exercises to re-establish binocularity, in addition to using occlusion and a prism.^12,102 Brief descriptions of these interventions follow. The treatment option selected for a client depends on the prognosis for recovery, the client’s ability to participate in therapy, family and financial resources, and the eye specialist providing consultation.

1. What determines whether treatment intervention is needed for a client with a visual impairment?

2. What three aspects of environments/tasks can be modified to increase their visibility for a client with visual impairment?

3. What prevents a client from automatically compensating for a VFD by turning the head farther to see around the blind field?

4. What kind of protective behaviors do persons adopt following onset of a VFD? Why do they adopt these strategies?

5. What is the normal search pattern executed by most adults when viewing an unstructured visual array? A structured array?

6. What is the primary compensatory strategy taught to the client with hemi-inattention?

7. What is the most crucial lower-level visual process contributing to the ability to complete visual cognitive processing?

8. What changes occur in the visual search pattern of a client with hemi-inattention?

9. When would partial occlusion be used for the client? Describe the technique used to apply partial occlusion.

10. How does convergence insufficiency affect reading performance?