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Show Rehabilitation for Visual Disorders Susanne Trauzettel-Klosinski, MD Abstract: Rehabilitation for visual disorders demands thorough assessment of many components of vision and a tailored strategy of maximizing residual function. Magnification with optical or electronic aids and the use of eccentric fixation and specific reading training exercises are helpful techniques in patients with central scotomas. Visual exploration training is beneficial in patients with homonymous hemianopias. Journal of Neuro-Ophthalmology 2010;30:73-84 doi: 10.1097/WNO.0b013e3181ce7e8f 2010 by North American Neuro-Ophthalmology Society Many diseases of the eyes and visual pathways are associated with persisting visual deficits that require rehabilitation. There is an increasing demand for rehabil-itation for these disorders (1,2), particularly in view of increased survival rates and prolonged life expectancy (3-5). A precondition for successful rehabilitation is an exact assessment of visual impairments. The World Health Organization general classification of impairments, dis-abilities, and handicaps (ICIDH) (6), later modified to the International Classification of Functioning, Disability and Health (7) can be well adapted to the visual system (Fig. 1). It considers 3 fields: 1) impairment, which assesses the pathologic condition and the function on the basis of the involved organ(s); 2) disability or activity limitation, which indicates the difficulties caused by the impairment; and 3) handicap or participation restriction, which stands for the resulting problems in the patient's environment. DIAGNOSTIC PROCEDURES IN VISUAL REHABILITATION Determination of visual acuity for distance and near viewing, refractive error, and accommodative amplitude and the optimal prescription of glasses come first. Visual fields must also be determined accurately, because defects involving the central field limit the size of the reading visual field (,5 from fixation). Visual field defects in the periphery can lead to orientation difficulties. To detect small defects, one must use a dense grid or a thorough manual strategy. If perimetry cannot be performed with a standardized instrument, bedside confrontation fields are useful to detect large field defects, especially hemianopias. Tangent screen campimetry may also be used. Contrast sensitivity testing is also critical. Contrast can be improved by optimal illumination or by marking the environment with special high-contrast landmarks. READING In modern society, adults spend approximately 2.5 hours per day reading, especially during work activities. Approx-imately 90% of all jobs require dealing with written material (8). To read newspaper print at a distance of 25 cm, a visual acuity of at least 20/50 (0.4) is necessary. Whereas visual acuity testing depends on recognizing only 1 optotype at a time, reading demands a simultaneous overview of a group of letters. The minimum reading visual field (9) is an area of approximately 2 to the right and left of fixation and corresponds approximately to the ‘‘visual span'' or ‘‘word recognition span'' (10,11). Within this area, letters are seen clearly. Figure 2A shows the functional and morphologic data related to a fundus image. The ‘‘minimum reading visual field'' (turquoise oval) corresponds more or less to the area of the fovea (green oval). Parafoveal information processing can extend the total ‘‘perceptual span'' (‘‘reading visual field'') during 1 fixation in the reading direction up to 15 letters (11,12) (Fig. 2B, red oval). This extended perceptual span provides in-formation about word length, capitalization, and word shape, and offers a preview benefit, which is useful in guiding the next saccade to the appropriate landing position. For fluent reading, a total perceptual span of 5 (15 letters) to the right and 1.3-2 (4-6 letters) to the left of fixation is necessary, as shown in window experiments in Low Vision Clinic and Research Laboratory, Center for Ophthal-mology, University of Tu¨bingen, Tu¨bingen, Germany. Address correspondence to Susanne Trauzettel-Klosinski, MD, Low Vision Clinic and Research Laboratory, Center for Ophthalmology, University of Tu¨bingen, Schleichstrasse 12-16, D-72076 Tu¨bingen, Germany; E-mail: susanne.trauzettel-klosinski@uni-tuebingen.de Trauzettel-Klosinski: J Neuro-Ophthalmol 2010; 30: 73-84 73 State-of-the-Art normal subjects (12) and in patients with homonymous hemianopias (13). The perceptual span is a dynamic parameter that is also influenced by top-down mechanisms, such as visual attention. During reading, the holding positions of the eyes between saccades have a mean duration of 250 ms (14). In normal subjects, eye movement recordings show a typical staircase pattern, a sequence of saccades and holding positions (Fig. 8A). Information processing occurs during the holding positions. The retinal area used for reading comprises only a few square millimeters but is highly magnified in the visual cortex (15). The central 10 diameter of the visual field, which accounts for approxi-mately 2% of the total visual field, is mapped onto nearly 50% of the primary visual cortex (16,17). ASSESSING READING ABILITY IN LOW VISION PATIENTS Refractive Error Exact determination of refractive error is necessary in low vision patients. If visual acuity is #20/200, the measure-ment should be performed by ETDRS charts because they allow more steps in the low vision range by reducing the distance. Measuring near visual acuity and range of accommodation are also important here. Magnification Assessing whether magnification would be helpful is an important step. The smallest print size that can be read fluently corresponds to the magnification need. Even though there is a reciprocal mathematical relationship between visual acuity and magnification need, in reality there is often a discrepancy. Reading Speed Reading speed should be determined by having the patient read a paragraph of text aloud. A whole paragraph of text is preferable to a single sentence for more accurate speed measurement and judgment of fluency and mistakes. For this test, a newly developed set of equivalent texts in dif-ferent languages is available (18, http://www.amd-read.net). Fixation Behavior Knowledge of fixation behavior is helpful if discrepancies between good visual acuity and impaired reading perfor-mance arise (as in ring scotomas, see below). Clinical methods of judging fixation are 1) determination of the blind spot in perimetry (Fig. 3C); 2) sighting the position of the corneal reflexes when the patient looks at the examiner; and 3) noting the fixation locus and motion of the eye during direct ophthalmoscopy. Further methods are fixation photography and fixation behavior determined with the scanning laser ophthalmoscope (SLO) (Fig. 4). Parafoveal Contrast Sensitivity Testing This testing provides valuable information on parafoveal deficits (19,20), which can precede central visual loss (20). Eye Movements Recording of eye movements during reading is a valuable method of showing ocular motor behavior during reading. FIG. 1. World Health Organization (WHO) classification of impairments, disabilities, and handicaps (ICIDH) (6) and of functioning, disability and health (ICF) (7) adapted to visual rehabilitation. (Modified from Reference 45.) State-of-the-Art 74 Trauzettel-Klosinski: J Neuro-Ophthalmol 2010; 30: 73-84 FIG. 2. A. Reading-relevant morphologic and functional data on a fundus image. Visual acuity (yellow) decreases rapidly with increasing eccentricity, as does cone density (dark blue). The proportions of the foveola (1 , green circle) and the fovea (5 diameter, green oval) determine the minimum reading visual field (turquoise oval) of 2 to the right and left of fixation and 1 above and below fixation. B. The data in A are related to a reading text. Because of the visual acuity curve (yellow), only in the minimum reading visual field (turquoise oval) can the text be perceived clearly. The total perceptual span (red oval) can be extended up to 5 (or 15 letters) in the reading direction by parafoveal information processing. (Modified from References 22 and 47). State-of-the-Art Trauzettel-Klosinski: J Neuro-Ophthalmol 2010; 30: 73-84 75 REHABILITATION FOR RETINAL AND OPTIC NERVE DISEASES Central Scotomas Patients who have central scotomas that cover the reading visual field can learn to use eccentric fixation (21) in an intact area of the visual field at the margin of the scotoma (22-24). The new fixation locus becomes the new center of the visual field (25,26). This eccentric fixation locus is called the ‘‘preferred retinal locus'' (PRL), even though patients often use more than 1 eccentric locus. The eccentric retinal area used for reading does not have sufficient resolution to read normal newspaper print, so that the ability to read can be regained only by magnifying the text (Fig. 3). Eccentric fixation plus magnification of the text is the basis for the effectiveness of magnifying visual aids in patients with a central scotoma (Fig. 4.). The shift of the scotoma toward the upper visual field theoretically represents the most favorable situation for reading. The line of text becomes free for reading and the lower visual field remains free for spatial orientation on the page. However, not all patients show this favorable fixation behavior. Some 20%-50% of patients shift the central scotoma to the right or left of the normal fovea (23,27-29). It is hard to explain why such an unfavorable fixation locus would be chosen. However, apart from the resolution at a certain eccentricity, sustained focal attention, which facilitates stimulus discrimination (19,30,31), influences the choice of a PRL location. Patients with good attentional capabilities in the lower visual field install their fixation locus below the scotoma. If attentional capabilities are reduced in the lower visual field, patients prefer a fixation locus to the left or right of the scotoma (19,32,33). Patients who have established an eccentric fixation locus can regain reading ability by text magnification. The spectrum of magnifying visual aids includes handheld magnifiers, stand magnifiers, simple high-plus spectacles, and telescopic spectacles. Handheld and stand magnifiers have the advantage of a comfortable working distance. When magnifying spectacles are used, the text has to be moved much closer, especially when simple FIG. 3. The minimum reading visual field (central square) related to the 30 visual field (upper panel) and a reading text (lower panel) in a normal subject (A) and in a patient with a central scotoma (B-C). B. When the patient has an absolute central scotoma and uses central fixation, the reading visual field is covered by the scotoma, so that reading is impossible. C. When the patient has an absolute central scotoma and uses eccentric fixation, the scotoma is shifted (here upwards) together with the blind spot, the reference scotoma (upper panel). The insufficient retinal resolution of this eccentric retinal area (middle panel) can be overcome with text magnification (bottom panel). (Modified from Reference 27.) State-of-the-Art 76 Trauzettel-Klosinski: J Neuro-Ophthalmol 2010; 30: 73-84 high-plus spectacles are used. Telescopic magnifying spectacles allow a longer viewing distance, but they are cosmetically unfavorable. In patients with a magnification requirement of more than 8-fold, who have no experience with optical magnification, an electronic reading device, such as a closed circuit television (CCTV) monitor, should usually be chosen. It is important to provide sufficient illumination without glare or ultraviolet or infrared light (cold light source). It is helpful to be able to vary the brightness, which can be achieved by a simple dimmer switch. For far distance viewing, handheld telescopes are useful. The success rate of magnifying visual aids for reading is high. In a cohort of 763 patients in our low vision clinic, only 13% were able to read newspaper print before consultation; 90% were able to do so afterwards. Patients with a central scotoma (n = 293) showed a success rate of 94%. Those with age-related macular degeneration (AMD) (n = 191) showed a success rate of 94% (34), confirmed in a recent study with 835 patients with AMD (35). Training in reading involves proper handling of the visual aids, reading exercises with the aim of enlarging the perceptual span, optimizing eye movements (36), and learning to use the optimal retinal locus. Concerning this last component, several studies have reported posi-tive results (37,38), but there is considerable controversy about criteria and methods for choosing the optimal area (39). Ring Scotomas These defects may easily remain undetected because visual acuity can be good. However, a discrepancy between good visual acuity and impaired reading performance often indicates a ring scotoma. The central seeing island may be too small to include a sufficient number of letters for fluent reading (Fig. 5, 5.2, 5.4, 5.8). If patients learn eccentric fixation for reading magnified texts, they can regain reading ability. Constricted Fields In degenerative retinal diseases and in the late stage of glaucoma, visual fields are often constricted (Fig. 5, 5.3 and 5.9). The central seeing island may be too small for reading, and no peripheral visual field area is available. Reduction of letter size with contrast enhancement may be helpful. When the constriction limits the field to less than 30 , orientation and mobility will be impaired. FIG. 4. Fixation of a target and of a line of text observed with the scanning laser ophthalmoscope in a normal subject (A-B) and in a patient with a central scotoma due to Stargardt's disease (C-D). (The text is seen as upside down only for the examiner; it appears upright to the patient.) The patient can read the text with the eccentric retinal locus and 2.5-fold magnification. State-of-the-Art Trauzettel-Klosinski: J Neuro-Ophthalmol 2010; 30: 73-84 77 CHIASMAL DISORDERS In patients with bitemporal hemianopia, the limited temporal fields cause orientation problems. Depth percep-tion may be impaired, which leads to difficulties with near distance tasks such as sewing, threading needles, or using precision instruments. In these cases, convergence causes crossing of the 2 blind temporal hemifields, resulting in a completely blind triangular area posterior to fixation (40). Hemifield Slide Phenomenon Another problem is the hemifield slide phenomenon (Fig. 6), which results from the lack of a normal overlap of the nasal visual fields and which prevents fusion. Therefore, preexisting phorias easily develop into tropias. In cases of preexisting esophoria or intermittent esotropia, patients will experience a separation of the nasal hemifields, causing a blind area in the center of the field. Patients with preexisting exophoria or intermittent exotropia will have an overlap of the 2 hemifields, and patients with preexisting hyperdeviations will experience a vertical separation of the images crossing the vertical meridian (40). The hemifield slide phenomenon can be especially disabling in reading long numbers in tables and bank statements. Patients must be made aware of the hemifield slide phenomenon to guard against misinterpretations of reading material. Monocular reading can be helpful in such cases. The use of a ruler can be a valuable aid to improve navigation on the page. FIG. 5. The principal visual field defects in retinal, optic nerve, and bilateral occipital lobe lesions. The visual rehabilitative approach is based on the functional effects of the field defect independent of its origin. State-of-the-Art 78 Trauzettel-Klosinski: J Neuro-Ophthalmol 2010; 30: 73-84 Retrochiasmal Disorders In retrochiasmal lesions, the visual field defect is homon-ymous, sometimes limited to a quadrant. It may spare or split the macular (fixational) region. When the lesion spares the occipital pole, macular sparing of 2-5 in the blind hemifield along the 0 meridian often occurs (16,17,41,42). If the occipital pole is spared, the visual field will be constricted with defects respecting the vertical midline and showing a ‘‘step'' at the vertical midline (Fig. 5, 5.11). An isolated lesion of the occipital pole causes a small paracentral homonymous hemianopic defect. Bilateral occipital pole lesions may produce binocular central scotomas (Fig. 5.10). Visual rehabilitation is conducted along the guidelines described earlier for central scotomas and constricted fields, except that the problem may be even more challenging as the defects are always binocular. Retrochiasmal lesions may be associated with traumatic brain injury (TBI), an important cause of disability (43-45). TBI often includes perceptual disorders, which are frequently overlooked (46). Their rehabilitation requires a multidisciplinary approach. Reading With Homonymous Hemianopia When the field center is involved (‘‘macular splitting''), homonymous hemianopia causes severe reading problems because half of the reading visual field is missing (Fig. 7A). In ‘‘macular sparing,'' the reading visual field may be preserved and reading can be normal (Fig. 7B). Paracentral homonymous scotomas typically cause severe problems with reading because they obscure half of the reading visual field (Fig. 7C). These small paracentral scotomas are often overlooked in automated perimetry if the grid of the test program is not dense enough. The severity of the reading problem in homonymous hemianopia is also influenced by the side of the defect in relation to the reading direction. In left-to-right readers, a right homonymous hemianopia is extremely impairing because the patient cannot see the oncoming groups of letters or words (Fig. 8C) (13). On the other hand, a patient with left homonymous hemianopia gets through the line quite easily but has difficulties finding the beginning of the next line (Fig. 8B). Eccentric fixation may help some patients with macular splitting (Fig. 9). The use of eccentric fixation (Fig. 9A) causes a little sacrifice of visual acuity but creates an extended perceptual span that is crucial for fluent reading (Fig. 9B). Eccentric fixation causes a shift of the field defect toward the hemianopic side in conventional perimetry (Fig. 10B), which can be misinterpreted as improvement of the visual field. This process indicates high cortical plasticity, because the new eccentric fixation locus is used not only as the new center of the visual field, but also as the new center of the coordinates of the reading eye movements, which means a shift of the sensory and motor reference (47). Patients spontaneously develop unstable asymmetric fixa-tional eye movements with saccades toward the hemianopic side (Fig. 10A). This phenomenon also leads to a shift of the vertical field border in conventional perimetry (Fig. 10B). Rehabilitation of the Hemianopic Reading Disorder Orientation on the page can be improved by visual and tactile tools such as a ruler or a forefinger, especially in guiding patients with left homonymous hemianopias in finding the beginning of the next line of text. Another approach is turning the text to a vertical or diagonal orientation, but this technique has never been tested in a large patient group. Training in predictive saccades can be beneficial in those with left homonymous hemianopias. Such saccades improve their ability to find the beginning of the next line of text. Scrolled text training programs have been shown to be effective in this regard (48-50). Hemianopic Orientation Disorder Patients with homonymous hemianopias are severely impaired in regard to spatial orientation. However, many spontaneously develop a beneficial compensation strategy: exploratory saccades toward the hemianopic side for better usage of their field of gaze. FIG. 6. Hemifield slide phenomenon in bitemporal hemianopia. Exodeviation leads to an overlap, esodeviation to a gap, and hyperdeviation to a vertical misregistry of the hemifields, causing severe reading disability, especially for long rows of digits. (Modified from Reference 40.) State-of-the-Art Trauzettel-Klosinski: J Neuro-Ophthalmol 2010; 30: 73-84 79 This spontaneous compensation strategy can be sup-ported and improved by saccadic training (see below). Fig. 10C shows the shift of the field defect by saccades in a natural scene. In conventional perimetry, this behavior shifts the field defect to the blind side (51), a pattern that can be misinterpreted as an improvement in the visual field (compare Fig. 10B-C). In saccadic search paradigms, a development of saccadic strategies can be observed. In early stages, patients often use a staircase pattern of saccades to find the target (Fig. 8B) and later show overshoot as a predictive strategy (52). Optical Devices Most patients are confused by the double images and disturbances in spatial orientation caused by optical devices used in an attempt to improve vision in homonymous hemianopia. Binocular sector prisms cause a relocation of the field or a shift of the position of the field loss (53). Although binocular prisms are not effective in treating FIG. 8. Eye movements during reading 1 line of text. A. The normal subject needs 8 saccades per line and approximately 1.5 seconds. B. The patient with left homonymous hemianopia gets through the line quite easily but has difficulty finding the beginning of the next line and makes several small regressions during the return sweep. C. The patient with right homonymous hemianopia makes numerous forward and backward saccades to get through the line; reading speed is prolonged 6-fold over normal. FIG. 7. Right homonymous hemianopia related to the 30 visual field (upper panel) and to the reading text (lower panel). A. In macular splitting, one half of the reading visual field is covered so that reading is impaired. B. In macular sparing, the reading visual field is spared, and reading is normal, although the large field defect hinders orientation. C. In a lesion of the occipital pole, a small paracentral homonymous field defect occurs, which causes severe reading disability. (Modified from Reference 76.) State-of-the-Art 80 Trauzettel-Klosinski: J Neuro-Ophthalmol 2010; 30: 73-84 hemianopia, they have been shown to be beneficial in patients with hemispatial neglect (54). Monocular prisms and mirrors have been used to shift the image of the blind hemifield toward the normal hemifield (55). Unfortunately, these devices usually cause diplopia and confusion. Creating confusion is intentional, because it induces an eye or head movement toward the blind side. However, the diplopia in the central visual field is described as very unpleasant (55). Even so, Hedges et al (51) reported a benefit in 20% of their patients. Monocular sector prisms placed across the whole width of the lens, but only in the peripheral field, have been reported to be beneficial by expanding the field without causing central diplopia. In 1 study (56), 47% of the patients were still wearing the peripheral prisms after 12 months. However, there was no control group and no control treatment in that study. Optical aids may be helpful in a few patients, but these interventions cannot be generally recommended. Training to Improve the Hemianopic Orientation Disorder In evaluating the many programs that allege success, the following issues should be considered: 1) spontaneous recovery must be ruled out, especially in the first weeks after the neurologic insult (spontaneous recovery normally does not occur after 6 months) (57,58); 2) a control group is essential; 3) the methods used to measure improve-ment must be reliable; and 4) the improvement must be durable. Spontaneous recovery may occur in 7%-53 % of patients, depending on the definition of improvement and the cohort of observed patients (57,59,60). Hier et al (61) reported an improvement of 60%-80%, probably due to compensatory strategies rather than a real change in the visual fields. The main problem with conventional perimetry in assessing improvement is insufficient fixation control. The vertical visual field border depends essentially on the quality of fixation. If fixation is unstable or eccentric, the visual field border is shifted toward the hemianopic side in conven-tional perimetry, which can mimic an improvement of the visual field defect (Figs. 9 and 10). This phenomenon has been shown clearly with fundus-controlled perimetry by SLO (41). Restitution Training Versus Compensation Training There are 2 different approaches in visual rehabilitation for homonymous hemianopia: restoration of lost visual field (‘‘restitution training'') and compensation strategies for visual field loss ("compensation training"). In 2 studies of restitution training, the stimulation has been at the border of the hemianopic field defect (62,63). Here the risk is stray light and especially eye movements toward the stimulus. The authors of the first study (62) reported an improvement of the visual field of up to 40 , but these results could not be confirmed by Balliet et al. (64). In a later study (63), ‘‘visual restitution therapy'' (VRT) was performed by presenting perimetric targets above the threshold along the visual field border. The authors described an extension of the seeing hemifield by approximately 5 . Our laboratory performed a SLO study before and after VRT using fundus perimetry with simultaneous fixation control and a grid of 0.5 spatial resolution horizontally and 1 vertically in the 10 visual field (65). Neither that study nor a study with conventional perimetry (66) could show any improvement in the visual field. Stimulation of the visual field using flickering letters and other targets in a more peripheral area (at 10 ) in the visual field was reported to normalize contrast sensitivity in the blind field in 2 patients (67). To examine this effect, our laboratory used a flickering letter stimulation at 22 FIG. 9 Eccentric fixation in homonymous hemianopia. A. Slight eccentric fixation causes a new functional midline, which causes a new perceptual area. B. In reading, this eccentric fixation creates a small reading visual field on the side of the blind hemifield by shifting the field defect toward the blind side. (Modified from Reference 76.) State-of-the-Art Trauzettel-Klosinski: J Neuro-Ophthalmol 2010; 30: 73-84 81 eccentricity (peripheral to the blind spot), a location that reduces the risk of eye movements toward the stimulus (68). No changes of the visual fields were observed. The reported effects of the 3 restitution studies (62,63,67) should be distinguished from the ‘‘blindsight'' phenomenon, which is an unconscious perception of visual stimuli via the superior colliculus to extrastriate regions without activation of striate visual cortex or V1 (69,70). Whether blindsight training can improve this kind of residual vision to a level that is relevant for everyday life is unresolved (71). The aim of compensation training is to enlarge the field of gaze by frequent eye movements into the blind hemifield and by shifting attention to the blind side. Such training has been reported to be effective in improving the use of the blind hemifield (50,72-74). A multichannel approach with additional acoustic stimuli was also reported to be beneficial (75). However, these earlier studies were done without a control group. 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