Visual Impairments Determining Eligibility for Social Security Benefits (2002) / Chapter Skim
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2. Tests of Visual Functions
2. Tests of Visual Functions
Pages 51-125
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From page 51... ...
Next we present the evidence on the testing of contrast sensitivity, followed by other visual functions that the committee judged worthy of consideration as candidates for testing by SSA most of which were mentioned in the earlier NRC report (National Research Council, 1994~. Some closely related functions are grouped in a single section.
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From page 52... ...
Visual acuity is typically measured under conditions of high contrast, using printed or pro jected charts with optotypes like those described above. The results of visual acuity testing are usually expressed in Snellen notation, which is the ratio of the test distance to the distance at which the critical detail of the smallest optotype resolved would subtend ~ minute of visual angle.
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From page 53... ...
, the visual acuity rating, VAR, where VAR = 100 - 50 (IogMAR) , and the Snell-Sterling visual efficiency (VE = 0.2-9.
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From page 54... ...
54 VISUAL IMPAIRMENTS TABLE 2-1 Conversion Table for Visual Acuity Notations Distance Vision LogMAR MAR MAR Decimal VE% VAR notation exact notation* notation*
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From page 55... ...
TESTS OF VISUAL FUNCTIONS Near Vision Snellen Fractions At 40 centimeters Based Based Based Snellen M x on on on notation Units Points height 20ft.*
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From page 56... ...
While there may be some further modifications to chart design or test procedures, it can be expected that letter chart testing will remain the standard means of measuring visual acuity.
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From page 57... ...
1^ ~~ v 10 ~ ~ ~ i~.0SM ~ ~ FIGURE 2-~. Sne~en-type acuity chart.
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From page 58... ...
On the basis of these recommendations, we identify four weaknesses in the current SSA standard: I in the SSA standard, the type of chastest to be used for testing visual acuity is specified only as "Snellen." There is no standardized Snellen chart.
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From page 59... ...
The recommended visual acuity chart design has two steps of size 20/125 and 20/160 between the 20/100 and 20/200 levels, and it is also recommend that credit be given for partial success in reading the sample of letters at each size. The SSA standard for Tmpairment of Central Visual Acuity is that the visual acuity should be 20/200 or worse.
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From page 60... ...
Design There is general agreement that the design of a visual acuity chart should be such that the visual task is the same at each size level, so that size remains the only significant variable from one size level to the next (Bailey & Lovie, 1976~. For this principle to be satisfied, the size progression should be logarithmic, there should be the same it,
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From page 61... ...
between each row and the next. Observation Conditions For assessment of distance visual acuity, test distance should be 3 meters (10 feet)
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From page 62... ...
Source: National Eye Institute National Institutes of Health. OD K o~ :~ oh O.f Eli t .2 ..3 for shortening of the viewing distance to 1 meter when a visual acuity of 4/40 (equivalent to 20/200)
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From page 63... ...
and, if the goal is to assess functional disability, it may be appropriate to take additional measures of visual acuity at nonstandard luminance levels. Glare conditions should be avoided.
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From page 64... ...
(American Medical Association, 1993; American Medical Association & the Committee on Medical Rating of Physical impairment, 1958) for calculating binocular visual efficiency took the monocular acuity of the better eye and added a negative weighting dependent on the visual acuity in the worse eye.
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From page 65... ...
recommended defining visual acuity as the smallest size at which at least 7 out of 10 optotypes are read correctly. The committee indicated that acuity could alternatively be specified as the last optotype size at which all letters were read, plus the number of optotypes read at the next smaller size (e.g., 20/30+3)
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From page 66... ...
Tf the near vision test chart has the same or similar design features as the letter chart used for distance visual acuity, if other test conditions (luminance, contrast, etc.) are the same, and if the subject is wearing appropriate refractive error correction, then the distance and near visual acuity scores should be equivalent to each other.
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From page 67... ...
Given the history and legislation behind the current SSA standard of "20/200 or worse distance acuity" as the principal criterion for visual disability, we recommend continued use of the 20/200 criterion. Since we recommend a visual acuity chart design that would include optotypes at the 20/160 level, applying the "20/200 or worse" criterion literally to scores obtained with such a chart would set the effective criterion to "worse than 20/160 distance acuity." The scoring of the charts currently used in disability determination sets the effective criterion at "worse than 20/100." 67
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From page 68... ...
From the published relationships between acuity and functional abilities, it might be predicted that an individual with reduced visual acuity would have certain deficits in functional abilities in several different functional tasks. However, the individual is likely to function better than expected at some tasks and worse at others.
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From page 69... ...
in normal eyes, the total monocular visual field extent is approximately 160° horizontally and 100° vertically. The visual fields of the two eyes overlap, except for the far temporal visual field of each eye.
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From page 70... ...
Peripheral and central vision have been found to be important for performing many daily activities, and people with significantly restricted visual fields experience many difficulties with occupational demands and other activities (Gutierrez et al., 1997; Johnson & Keltner, 1983; LovieKitchin, Mainstone, et al., 1990; Lovie-Kitchin, Woods, et al., 2001; Marron & Bailey, 1982~. As mentioned earlier, visual field measurements are currently used by SSA as part of their visual disability determination procedures.
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From page 71... ...
Turano and colleagues have reported that people with either central or peripheral visual field loss exhibit a deficit in the visual stabilization of body sway (Turano, Dagnelie, & Herdman, 1996; Turano, Herdman, & Dagnelie, 1993~. Tn addition, they have reported deficits in mobility performance in people with restricted visual fields due to glaucoma or retinitis pigmentosa (Geruschat et al., 1998; Turano et al., 1999~.
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From page 72... ...
was significantly influenced by total visual field extent. individuals with smaller visual field extents had poorer mobility performance.
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From page 73... ...
Deficits in the useful field of view are more prevalent in older drivers than is traditionally measured visual field loss. Their findings suggest that the useful field of view may be a better predictor of accidents than visual fields or any other vision test.
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From page 74... ...
However, any activity concerned with too} use/manipulation that incorporates a visual search task (e.g., detection of warning lights on a pane} display, localization of oh jects to reach) may be affected by visual field loss, particularly if it is severe loss in both eyes.
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From page 75... ...
TESTS OF VISUAL FUNCTIONS 135° 1 80° Right Eye (O.D.)
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From page 76... ...
There are several problems associated with the current method of making disability determinations for visual field loss. First, there is the very practical issue that Goldmann perimeters are becoming increasingly scarce, and fewer individuals have the proper training for performing kinetic testing on the C;oldmann perimeter (Anderson ~ Patella, 1999~.
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From page 77... ...
We conclude from our study of available perimetry methods that automated threshold static perimetry procedures should be employed as the method of performing visual field disability determinations. To ensure that accurate, reliable and valid results are obtained, we also recommend that an automated static perimeter meet the following criteria to be considered as an approved visual field device for SSA disability determinations: I
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From page 78... ...
if the sub ject's sensitivity is lower, then the deviation is negative. Mean deviation or mean defect is thus the average sensitivity deviation from the normal values for all measured visual field locations.
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From page 79... ...
Relation to Other Measures Visual field measures can be somewhat independent of visual acuity, contrast sensitivity, color vision, stereopsis, and other central visual function measures. For some disorders, visual field loss can be present when visual acuity and contrast sensitivity are normal.
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From page 80... ...
Automated threshold testing of the central 30° radius seems to be the most appropriate means of obtaining the best visual field information for disability determinations. Recently, there was an investigation of an experimental automated kinetic perimetry procedure implemented on the Humphrey Field Analyzer (Odom et al., 1998~.
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From page 81... ...
The AMA guidelines are not based on empirical data, the procedures have not been validated, and their properties are largely unknown. To account for scotomas and normal visual field locations between major meridians, we recommend that an index of the overall visual field status be used for disability determinations.
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From page 82... ...
Thus, the recommended visual field criterion for SSA disability determinations would be an MD in the better eye of -22 dB or worse. Issues Needing Further Study Aside from studies of driving and a few investigations of mobility performance in people with low vision, there is currently very little information on the relationship between the status of the visual field and performance of daily activities, occupational demands, and task performance.
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From page 83... ...
Another area in need of future research is the development of techniques for providing valid and reliable measures of binocular visual field sensitivity. CONTRAST SENSITIVITY Description Contrast is a measure of the differences in luminance (brightness)
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From page 84... ...
Pelli-Robson contrast sensitivity chart (Pelli, Robson, & Wilkins, 1 988~. Reproduced by permission of Denis Pelli.
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From page 85... ...
For example, contrast sensitivity tests may be sensitive to visual loss caused by cataracts, glaucoma, and multiple sclerosis (diseases in which impairment in contrast sensitivity is common) , in sub jects with little or no loss in visual acuity (Regan, 199Ib)
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From page 86... ...
(1999) suggest that a PelliRobson contrast sensitivity score of less than 1.5 would result in visual impairment and a score of less than 1.05 would result in disability.
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From page 87... ...
. in contrast, for those with visual impairments, a number of studies have shown an association between contrast sensitivity and mobility (Geruschat et al., 1998; Kuyk & Elliott, 1999; Kuyk, et al., 1998; Marron & Bailey, 1982; Rubin, et al., 1994; Turano et al., 1999~.
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From page 88... ...
Combining visual field measures with contrast sensitivity provided the best predictor of mobility performance. Contrast sensitivity is a better predictor of driving performance than visual acuity.
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From page 89... ...
Another difficulty is that test-retest reliability for the Vistech charts has been shown to be lower than for some other contrast sensitivity tests (Rubin, 1988~. Reliability is a critical requirement for disability determination.
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From page 90... ...
in addition to the Vistech, there are also several low (fixed) contrast letter charts available, as well as CRT-based contrast sensitivity tests.
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From page 91... ...
In short, a lO-fold loss of letter contrast sensitivity would be quite disabling. Relation to Other Measures Contrast sensitivity measures provide information that is related to, but is also distinct from, high-contrast visual acuity measures.
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From page 92... ...
may show significant contrast sensitivity loss with little visual acuity loss and, as discussed in Chapter 3, contrast sensitivity is a better predictor of mobility and reading performance than visual acuity. Quality of /nformation Avai/ab/e A number of different contrast sensitivity tests are available.
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From page 93... ...
Therefore, we recommend adding contrast sensitivity as an additional basis for disability determination for individuals with visual acuity between a lower limit of 20/50 and an upper limit of 20/200. Tt is not necessary to measure contrast sensitivity in individuals who meet the SSA medical listings criteria for visual acuity or visual fields, but it is recommended for those with visual acuity between 20/50 and 20/200 and other indications or self-report of serious visual impairment.
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From page 94... ...
94 Q Ct ._ An LO En En Cal o o .
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From page 95... ...
exist for this condition, but they have not been extensively used with working-age visually impaired subjects and therefore require further study. Another area requiring further study is the contrast sensitivity testing of young children (see Chapter 4~.
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From page 96... ...
and the Farnsworth pane} D-15 test (which distinguishes individuals with severe color vision deficiencies from those with normal color vision or only mild color vision losses)
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From page 97... ...
This list represents a very small subset of the total number of occupations in the general workforce. Quantifying Performance Several varieties of color vision tests are used for clinical and occupational purposes.
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From page 98... ...
The D-15 test clearly distinguishes persons with severe color vision deficiencies and those with normal color vision or only mild to moderate deficit. Tt also is able to accurately determine the type of color vision deficiency (red/green/blue)
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From page 99... ...
Color vision has a minor or negligible role for most jobs, and we recommend that it not be considered further with regard to visual disability determination.
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From page 100... ...
With the eyes looking ahead, each eye's field extends about 95° toward the temple and about 55° toward the nose in Caucasians (Fischer & Wagenaar, 1954~. The overlapping region is known as the binocular visual field and normally spans horizontally the central 110°.
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From page 101... ...
or binocular nvalry, a sometimes haphazard switching of vision from one eye to the other. Binocular function is unusually sensitive to visual experience during development.
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From page 102... ...
102 VISUAL IMPAIRMENTS Evaluation Why the Measure Might Be Usefu/ Failure to combine information from the two eyes can lead to a reduced ability to see small differences in depth. Moreover, under some circumstances, the vision of the two eyes might conflict, making vision poorer than if one eye alone was used.
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From page 103... ...
The Lang stereo test is also similar, except that it uses a Fresne} lens above the test plate to produce slightly different images to the two eyes, while avoiding the need for special glasses. Recommendations Our recommendations here concern impairments of binocular function and are distinct from our recommendations in other sections that other visual functions should be tested binocularly.
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From page 104... ...
Although visual search is not a basic visual sensory function, it is a function of the visual system and can therefore be considered a visual function as defined in Chapter 1. Previous research on normally sighted persons has demonstrated that it is possible to predict visual search performance in laboratory tasks on the basis of visual sensory factors, such as visual acuity, contrast sensitivity, and visual field sensitivity (Carrasco & Chang, 1995; Carrasco & Frieder, 1997; Geisler & Chou, 1995; Verghese & Nakayama, 1994~.
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From page 105... ...
Recommendations .., Given the available evidence to date, the committee recommends at this time that a test of visual search ability not be used in the visual disability determination process. Since visual search is a fundamental aspect of seeing, further work is needed to clarify the relationship between visual search impairments and the performance of workrelated tasks.
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From page 106... ...
Vision at Low Light Levels The normal visual system can adapt to a wide range of light levels, although acuity and contrast sensitivity are reduced as light level is reduced. However, ability to function in low light is dramatically disrupted in aging (Adams et al., 1988; Sloane et al., 1988)
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From page 107... ...
, fundus albi punctatis, and glaucoma (GIovinsky et al., 1992~. Large changes in visual acuity can occur with relatively modest changes in illumination in many people with impaired vision (Lie, 1977; LovieKitchin & Bowman, 1985; Sloan, 1969~.
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From page 108... ...
The return to normal visual function is a gradual process; it may take many seconds but sometimes extends to over 30 minutes. Difficulty adapting to poor or changing light levels is widely acknowledged to have a serious impact on the mobility of many visually impaired persons (Geruschat & Smith, 1997; Sz~yk et al., 1990~.
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From page 109... ...
Disability glare can also be of retinal origin, when strong stimulation of one large region of the retina affects the sensitivity of other regions of the retina. The impact of veiling glare depends on the contrast and acuity demands of the visual task.
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From page 110... ...
is a hemispherical bow} with a controlled glare source held close to the eye, with a 12 mm aperture that allows the viewing of test targets. The clinician chooses the specific test task (e.g., ETDRS chart, Pelli-Robson chart, Bailey-Lovie low-contrast visual acuity chart)
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From page 111... ...
Meanwhile, the inclusion of contrast sensitivity testing should at least partly address the need for testing under less than ideal viewing conditions that are closer to those encountered in the real world. VISUAL EFFICIENCY SSA recognizes that impaired central acuity and impaired visual fields, neither of which alone would meet the disability standard in the listings, can in combination result in an overall impairment that is disabling.
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From page 112... ...
there is a logarithmic relationship between visual acuity and overall performance. Thus, for example, an acuity of 20/80 is as much worse than 20/40 as an acuity of 20/200 is worse than 20/100.
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From page 113... ...
Because of this, the committee recommends that the logMAR score be used directly in the computation of an overall measure of visual performance for disability determination, as described in the section on combining measures, below. There is no need to compute any index of central visual efficiency.
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From page 114... ...
. Taking normal log contrast sensitivity as 2.0, an expression of impairment that is commensurate with those obtained from the recommended measurements of visual acuity and visual fields would be 2 - CS.
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From page 115... ...
in the meantime, we recommend that SSA continue its current practice of giving equal weight to the measures of visual acuity and visual fields. Recommendations Beyond establishing commensurate scales for characterizing acuity, visual fields, and contrast sensitivity, we need to be able to compute an aggregate indicator of impairment.
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From page 116... ...
Recognizing that we must give equal weight to visual fields and to visual acuity (or contrast sensitivity) , but that we use either a measure of acuity or a measure of contrast sensitivity, we recommend that the overall measure of impairment should be computed as: aggregate impairment = logMAR + MD/22 when the scores to be combined are visual acuity and visual field and aggregate impairment = (2 - CS)
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From page 117... ...
suggest that the current acuity standard and the current visual field standard represent severely impaired vision. Nevertheless, the evidence also shows that overall visual performance varies continuously, and roughly linearly, with the measures of visual acuity, visual fields, and contrast sensitivity that we have recommended.
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From page 118... ...
Children An aggregate impairment score may be calculated for children who are old enough to be tested using the instruments designed for adults. RECOMMENDATIONS FOR TESTS OF VISUAL FUNCTIONS The committee's recommendations for the testing of visual functions for determination of disability focus on strengthening the testing of visual acuity and visual fields and adding one additional test, of contrast sensitivity, under certain circumstances.
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From page 119... ...
Since we recommend a visual acuity chart design that would include optotypes at the 20/160 level, applying the "20/200 or worse" criterion literally to scores obtained with such a chart would set the effective criterion to "worse than 20/160 distance acuity." The scoring of the charts currently used in disability determination sets the effective criterion at "worse than 20/100." The recommended charts have a 20/100 line that would allow SSA to maintain the criterion at the current effective acuity level, but SSA must make the decision on whether this should be done.
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From page 120... ...
We propose the following criteria for any perimeter to be used by SSA for disability determination: I The automated static perimeter should be capable of performing threshold testing using a white size TTT Goldmann target and a 31.5 apostilb (10 cd/m2)
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From page 121... ...
Contrast SensitivityTesting The committee recommends that contrast sensitivity be assessed as an additional basis for disability determination for claimants who do not meet the current medical listing criteria for disability, but who have acuity between 20/50 and 20/200 and show other evidence or self121
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From page 122... ...
Testing of binocularity, visual search, and adaptation to glare and luminance change, although worthy of further study because of their potential importance to visual task performance, are not recommended with the tests now available. Well-documented severe impairments of visual functions other than acuity, fields, or contrast sensitivity could be taken into account as "adjustments" in the disability determination process.
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From page 123... ...
We need only add the scores to compute an overall measure. Recognizing that we must give equal weight to visual fields and to visual acuity (or contrast sensitivity)
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From page 124... ...
as well as to tests of basic visual functions. Research Recommendations Research is needed relating the outcome of visual assessment using such tools as visual acuity charts to an individual's ability to function in the workplace and in society.
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From page 125... ...
New tests are available to test low luminance, low-contrast acuity, but they have not been extensively used among working-age visually impaired people and therefore require further study, which would also be useful for tests of binocularity and of visual search and related functions.
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