Visual Impairments Determining Eligibility for Social Security Benefits (2002) / Chapter Skim
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3. Visual Task Performance
3. Visual Task Performance
Pages 126-198
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From page 126... ...
currently relies primarily on tests of basic, ob jectively testable visual functionsnamely, acuity and visual fields with the implicit assumption that these measures can predict ability to perform visually intensive work and daily life tasks. As understanding of the complexity of the relationship between the traditional measures of visual function and an individual's actual abilities to perform important tasks has grown, SSA has become concerned about the predictive validity of such tests and specifically requested the committee to explore the possibility of using measures that more directly test the ability to perform daily life and work tasks.
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From page 127... ...
The committee sought evidence to demonstrate (through both direct observation and self-report) the nature of the relationships between visual function measures such as acuity, visual fields, contrast sensitivity, and others and the actual ability of individuals in a community setting to perform important daily life tasks and other vision-related tasks that would be of importance in a job setting.
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From page 128... ...
First we present the findings on the importance and relationships to visual functions of each of the four task domains: reading, mobility, social participation, and too} use and manipulative tasks. These sections include reviews of available tests for these task domains and recommendations on the use of such tests for disability determination.
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From page 129... ...
The same person with no change in eye disorder or measured impairment might improve his or her reading performance as a result of rehabilitation. Reading also differs from clinical tests of visual impairment in being dynamic in character.
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From page 130... ...
Given the importance of reading to employment and other activities of daily life and the imprecision of estimating reading disability from traditional measures of visual impairment, a strong case can be made for including evaluation of reading performance in disability assessment. As described below, although reading performance is related to measures of visual impairment (acuity, contrast sensitivity, and field)
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PeonIe with mild to moderate visual impairment mav use optical 1 magnifiers, requiring coordination of hand movements, head movements, and eye movements. People with more severe visual impairment may use electronic magnifiers such as closed circuit TV.
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From page 132... ...
People with normal vision can read RSVP text much faster than conventional text (Rubin & Turano, 1992~. Despite high hopes for a similar improvement in speed for neonle with low vision, RSVP provides only a modest benefit 1 ~ 1 1 1 for readers with low vision (Fine & Peli, 1995; Harland et al., 1998; Rubin & Turano, 1994~.
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From page 133... ...
Although Braille reading speeds average about a factor of two lower than print reading speeds, Braille is especially valuable in contexts in which magnifiers or auditory displays are inconvenient. Word processing documents can be converted to Braille codes by software and embossed on Braille printers.
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From page 134... ...
While reading acuity documents the angular size of the smallest print size for which reading is possible, a somewhat larger print size is required for fluent, effective reading. For a given viewing distance, the critical print size, two or more times larger than acuity letters, is the print size beyond which the size of characters no longer inhibits reading performance.
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Reading acuity and critical print size are familiar measures to eye care professionals because of their similarity to letter acuity. The following measures are less familiar and have been used more in rehabilitation or research contexts.
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From page 136... ...
A sustainable reading speed of 176 wpm, while still slow for a normally sighted reader, would probably be adequate for meeting the needs of all but the most reading-intensive jobs. However, a person whose maximum reading speed is 90 wpm or less is functionally disadvantaged in reading, lying more than two standard deviations below the normal mean (Legge et al., 1992~.
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From page 137... ...
in one study, a discrepancy was found in the responses of some people with mild visual impairment between measured reading speed and self-reports of reading difficulty on the Activities of Daily Vision questionnaire (Friedman et al., 1999~. A small proportion of sub jects reported minimal difficulty in reading newsprint despite measured reading speeds less than 80 wpm.
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From page 138... ...
that can be read, but also an assessment of reading speed as a function of print size. Reading acuity, critical print size, and maximum reading speed are three important parameters for characterizing reading vision.
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, critical print size (arrow at the bend) , and reading speed (dashed liner.
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From page 140... ...
Print size should be expressed in angular terms when measuring reading acuity and determining profiles of reading speed as a function of print size. Specifying both the height of the print and viewing distance provides a measure of angle.
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if there is a fixed reading distance, the print size may be labeled in terms of angular size as Snellen fractions or logMAR values. Standardizing Testing Procedures The conventional or traditional reading distance is 40 cm, although other viewing distances may be used.
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(For specialized applications, it may be desirable to test reading performance in the left and right eyes separately.) Uniform instructions should apply across sub jects and across print sizes for a given sub ject.
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From page 143... ...
Assuming that reading disability needs to be ascribed to visual impairment, a diagnosed eye disorder or measurable visual impairment provides a prima facie case. If a nonvisual cause of reading disability is suspected, documentary evidence should be included in the assessment (e.g., a low score on the Mini-Mental Status Exam would be indicative of cognitive dysfunction)
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From page 144... ...
The measures of reading performance that have received most attention from clinicians and vision researchers are reading acuity, critical print size, and reading speed. These measures are all reactive to eye problems and are to some degree decoupled from one another.
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. An identical standard deviation of 0.l log units was obtained for a normal control group in a study of reading speeds for people with low vision by Legge et al.
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Re/ationship of Reading Performance to /mpairments of Visua/ Functions Reduced acuity, reduced contrast sensitivity, and loss of macular function are the primary visual impairments affecting reading for people with low vision.
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From page 147... ...
Conventional letter acuity measurements are not, however, good predictors of reading speed when adequate magnification compensates for acuity limitations (Legge et al., 1992; Whittaker & Lovie-Kitchin, 1993~. A recent report indicates that near acuity measurement, based on text or unrelated words, is predictive of reading speeds in people with macular degeneration (Lovie-Kitchin et al., 2000~.
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From page 148... ...
Hemianopsia refers to complete loss of either the left or right side of the visual field, usually due to stroke. Although both types of hemianopsias reduce reading speed, loss of the right visual field tends to produce greater deficits than loss in the left visual field (TrauzettelKlosinski & BrendIer, 1998~.
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proposed that a subset of people with low vision (those with cataract and other forms of cloudy ocular media) shows normal reading performance after loss of contrast sensitivity is accounted for.
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and viewing ~ ~ ~ , ~ distance. Normal reading speed is at maximum for angular print sizes over a lO-fold range from about 0.2 to 2.0 deg (Legge, Pelli, et al., 19851.
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More research is needed to clarify the effects of luminance on reading in people with low vision. The reading envelope of normal vision encompasses a wide range of print sizes, contrasts, and luminance levels.
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. A person whose critical print size is equivalent to 20/60 or less will be unable to read fluently most text in newspapers and other documents of equivalent print size if they are held at a normal reading distance.
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From page 153... ...
We recommend the following criteria for tests of reading vision: . Visual characteristics that are consistent with contemporary standards for acuity tests, including a logarithmic progression of · ~ print sizes; A range of print sizes containing large enough print to be useful with most visually impaired people and small enough to reliably measure reading acuity in normally sighted people; Text passages equated in layout across print sizes; Reproducible rules for estimating reading acuity, critical print size, and reading speed; Binocular testing, unless one eye interferes with the other in reading and the problem can be addressed by covering the interfering eye; and Text passages representative in font and letter spacing of commonly encountered real-world texts.
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From page 154... ...
Route memory has often been ascribed to people with blindness or low vision to explain deficiencies in spatial tasks (cf. Thinus-Blanc & Gannet, 1997~.
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This applies particularly to travel in unfamiliar surroundings which many blind and visually impaired
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Persons with some residual vision can add visual information about large ob jects that can serve as landmarks in the environment. Signs, once located, may be read with a hand-held telescope if visual function is sufficient.
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From page 157... ...
Studies of obstacle avoidance with low vision sub jects (again, mainly in well-controlled environments) have usually shown that acuity level is not important, contrast sensitivity is somewhat important, and the total extent of the visual field is of major importance (Haymes et al., 1996; Kuyk et al., 1998; Long et al., 1990; Lovie-Kitchin et al., 1990; Marron & Bailey, 1982~.
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From page 158... ...
However the major area in which acuity is vital is in finding and reading the signs on which one depends for orientation and navigation. Signs are designed in overall size and in print size to be located and read by individuals with normal or nearnormal acuity from the distance at which their particular information is needed (20/40 is a common standard for road signs)
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From page 159... ...
They found no effect of acuity level, but people with early onset of narrow visual fields tended to perform more poorly than others. Reduced field size could affect other aspects of navigation by reducing the probability of finding or noticing landmarks and navigational signs.
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From page 160... ...
As noted in the discussion of theories of orientation and mobility, cognitive factors and memory abilities are important in orientation and navigation. For the mobility aspect of the task, the traveler often has to concentrate on the path ahead but be alert to hazards in the lower and horizontal visual fields.
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Summary and Recommendations The most important aspects of visual function for safe and efficient ambulatory orientation and mobility are contrast sensitivity, visual fields, and acuity. The next most important variable is adaptation to low or changing light conditions.
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. Measures of safety are often expressed statistically, such as a risk ratio or odds ratio in which a subgroup of drivers of special interest is compared with a reference group (e.g., visually impaired drivers compared with drivers who have 20/20 visual acuity or better)
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have shown that a 40° radius visual field and smaller can compromise some aspects of driving performance (e.g., road sign identification' obstacle avoidance, reaction time) (Wood & Troutbeck, 1992, 1995; Wood et al., 1993~.
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In studies addressing crash risk, drivers with severe binocular visual field loss (i.e., significant loss of peripheral vision in both eyes) appear to have twice the crash risk of those without this deficit (Ball et al., 1993; Johnson & Keltner, 1983~.
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From page 165... ...
Monocular truck drivers also reportedly carried out most maneuvers in a satisfactory fashion (McKnight et al., 1991~. With respect to safety, drivers of personal vehicles with monocular field loss did not have an elevated crash rate compared with a control group of drivers with normal visual fields in both eyes Johnson & Keltner, 1983~.
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From page 166... ...
Dynamic visual acuity has a stronger unadjusted association to driver safety than does the conventional static acuity test, but the relationship is still weak (HilIs & Burg, 1977; Shinar, 1977~. Three decades ago, a study showed that performance in a motion perception task was one of the best correlates of self-reported crash involvement among a large battery of vision tests (Shiner, 1977)
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From page 167... ...
However, there is no on-road driving evaluation with demonstrated validity and reliability for drivers of wide-ranging ages who are visually impaired. 1 to An alternative to measuring actual on-road driving performance is to use driving simulators.
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Slow visual processing speed and divided attention problems also increase crash risk at least twofold; these problems are not detected bv visual sensory tests (visual acuity. visual fields, contrast sensitivity)
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The committee considered the tests of visual function that may be related to social participation (see Chapter 2~. in addition, we reviewed the literature on vision-related tests that form specific analogues to social participation.
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From page 170... ...
required for recognition of identity and expression. These measures of performance were found to be very hi~hIv correlated to 1 _ ~ _ _ _ _ _ _ _ 1 ~ _ _ _ 1 ~ ` - ~ reading acuity scores and quite strongly correlated to letter chart visual acuity scores.
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From page 171... ...
in a comprehensive evaluation of vision in a population-based study, the SEE pro ject, the contribution of loss of visual acuity, contrast sensitivity, visual field loss, and stereoacuity has been characterized relative to the decline in the ability to match faces in an older population of 2,520 adults. The test comprised a series of 20 presentations of four faces; in each set of four, three are the same person in different poses, and one is a different person.
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From page 172... ...
(Scott et al., 1994~. Parrish et al., in a study of people with glaucoma, found that binocular visual field impairment was not highly correlated with decrements in social function as measured by the SF-36 or NET VFQ once visual acuity impairment was considered (Parrish et al., 1997~.
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From page 173... ...
Neither visual acuity impairment nor visual field loss was significantly associated, after also adjusting for gender, race, and education. Summary and Recommendations The importance of social interaction as a visually intensive task in the workplace environment is generally acknowledged.
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From page 174... ...
Depth perception and color vision were less likely to be reported as important across all tool use tasks. Research on the impact of vision loss, measured using standard tests, on performance involving use of tools in industry could not be located.
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From page 175... ...
in con junction with selected TADL tasks, such a battery might prove extremely useful in determining the extent to which an individual's visual impairment may influence safe and effective job performance. Because there is no standard set of performance-based tests, few studies in this area have been done, and tasks were selected that have 175
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From page 176... ...
. In another study, which combined visual acuity loss and/or visual field deficits into a category of "visual impairment," there was a correlation between visual impairment and performance on an index that included some tool use items (Haymes et al., 2001~.
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Self-Report of Tasks Using Tools Several scales in research instruments include the dimensions of reported difficulty with TADL tasks explicitly, although the tasks themselves may or may not involve the use of tools. Unlike the performance-based tests, however, self-report of difficulties includes not only perceived limitations imposed by vision loss, but also such dimensions as the impact from other comorbid conditions (such as arthritis)
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From page 178... ...
Summary and Recommendations While the committee acknowledges that too} use is an important component of daily activities and in the workplace, there are insufficient data to recommend any battery of performance-based tests that include tools that would determine visual disability for this domain. Data suggest that visual acuity loss and contrast sensitivity loss in particular are related to both self-report of difficulty and slower performance using tools.
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From page 179... ...
Even more basic are measures that assess only visual and integrative vision function, such as visual field or visual acuity, which have traditionally been used as markers of more complex levels of visual performance. At still more basic levels, electrophysiological tests, such as electroretinograms or visual evoked potentials, assess the physiological function of the visual system.
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From page 180... ...
For example, the traditional tests to assess visual function, even visual fields, are mostly ob jective physical measures. in contrast, self-ratings of functioning and well-being may be assessed by use of HRQOL questionnaires that are completed by the individual.
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From page 181... ...
and cataracts (Steinberg et al., 1994~. Modified for the effects of glaucoma and glaucoma treatment, it was included as one of several questionnaires that were used to assess the quality of life in the Collaborative Initial Glaucoma Treatment Study, another clinical trial sponsored by the National Institutes of Health Uanz et al., 2001~.
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From page 182... ...
Whatever visual difficulties are being experienced by the truck driver will not be adequately assessed by a measurement of acuity but will be characterized by a vision-targeted quality of life questionnaire. These results suggest that these questionnaires may in some instances measure visual disability better than routine testing of distance visual acuity with Snellen charts.
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From page 183... ...
on the peripheral vision subscale were associated with more visual field loss, but the strength of the correlation was relatively weak Uanz et al., 2001~. The National Eye institute Visual Function Questionnaire (NET-VFQ)
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From page 184... ...
with diminished vision functioning as measured by visual acuity and/or visual field, data relating a specific score to a specific level of functional performance or disability are not available. Thus, at present, a NET-VFQ score is not translatable to a specific level of visual acuity or visual field impairment.
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From page 185... ...
in an effort to better understand the relationships between visual skills and abilities and workplace requirements, the committee pursued several avenues of empirical data collection. First, an analysis of the most common standard vision measures visual acuity, visual fields, and contrast sensitivity in relation to actual performance on various tasks such as too} use and reading was conducted using the Salisbury Eye Evaluation study data.
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From page 186... ...
Together, these three efforts will, in the future, allow policy makers to better understand and refine the thresholds for determining vision-related disability for specific job categories. Job Analysis Using Labor Databases lob analysis is a process used to examine both the essential functions (i.e., important and frequent tasks)
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From page 187... ...
labor force" (McCormick & leanneret, 1988~. These job titles represent several hundred thousand actual analyses (i.e., multiple analyses of each job title, with the cumulative number of discrete observations varying for each job title from a few to several thousand)
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Usability of the PAQ Database The PAQ database includes 2,523 job titles with specific ratings. Each job was assigned to one of the nine DOL aggregate job categories, such as clerical or agriculture and fisheries.
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From page 189... ...
First, the data collected do not arise from a random sample of jobs within each of the i,817 unique job titles or the nine aggregate categories. Second, and even more importantly, among individuals with specific jobs, the selection of the sample may not be representative of all persons holding that specific job.
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From page 190... ...
The PAQ instrument gathers information on the following visual and perceptual characteristics of jobs: near visual acuity, far visual acuity, depth perception, and color discrimination. Tt does not include assessments of visual field or contrast sensitivity.
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From page 191... ...
As seen in Table 3-l, for the distribution of job titles in the database, far acuity, depth perception, and color perception are of low or minor importance or do not apply to 80 percent or more of respondents. However, 69 percent of the respondents rated near acuity as of moderate importance, with 10 percent rating it as of high or extreme importance.
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From page 192... ...
The levels are numerically coded as <3 = low or minor importance; 3 = moderate importance; 4 = high importance; TABLE 3-2 Rating of the importance of Vision to tote Performance by Broad Category of Job (percentage) Vision importance Prof/Tech Clerical Service Ag/Fish Near Acuity Not Applicable to Low 11 14 45 51 Moderate 77 82 46 49 High 11 4 ~ O Extreme 1 0 1 0 Far Acuity Not Applicable to Low 84 93 69 52 Moderate 11 4 23 24 High 4 3 5 19 Extreme 1 0 2 5 Depth Perception Not Applicable to Low 88 98 82 61 Moderate ~ 2 13 25 High 4 1 3 11 Extreme O O 1 3 Color Perception' Not Applicable to Low 87 94 80 89 Moderate 9 4 12 11 High 3 2 7 0 Extreme 1 1 1 0 (N)
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From page 193... ...
Service jobs and agricultural/fisheries jobs do not rate near acuity as important as do the professional/technical and clerical and sales jobs. However, depth perception is rated more important for jobs in agriculture/fisheries and benchwork, compared with professional and clerical jobs.
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From page 194... ...
exists only at the aggregate nine-category level, not for any of the 2,523 specific job titles nor across the aggregate of job titles; · Each of the 2,523 job titles has an unknown number of measurement sessions and an unknown number of observations per measurement session; The cumulative measurements for each job title are averaged over a 30-year time period and thus may not fully capture changes in workplace requirements as job functions change over time; · The PAQ was intended to be used for other purposes than the one the committee is undertaking; The vision variables are limited (no contrast sensitivity and no visual field items) and the near vision variable is measured differently from far vision, color, or depth perception.
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From page 195... ...
. 195 Analyses of the PAQ database demonstrate that near visual acuity is rated to be of high or extreme importance in 9.7 percent of 2,523 job titles, while far acuity is of similar import in 6.2 percent, depth perception in 4.9 percent, and color perception in 4.l percent.
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From page 196... ...
Reading tests are available that should be able to meet such criteria after modest additional research and development efforts, and we recommend that SSA support such research. We recommend the following criteria for reading tests: Visual characteristics that are consistent with contemporary standards for acuity tests, including a logarithmic progression of · ~ print sizes; A range of print sizes containing large enough print to be useful with most visually impaired people and small enough print to reliably measure reading acuity in normally sighted people; Text passages equated in layout across print sizes; Reproducible rules for estimating reading acuity, critical print size, and reading speed;
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Mobility The committee recommends no testing of ambulatory or driving mobility at this time. The evidence suggests that most ambulatory mobility problems will be captured by tests of visual functions: contrast sensitivity, visual fields, and acuity.
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Tests of visual acuity and contrast sensitivity should capture some of the relevant disability in social participation. Tests of social participation should not have high priority at this time, although they may merit reconsideration in the future.
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