PURPOSE. To determine the distribution of perceived visual ability for functio nal vision performance among persons with low vision in the Indian state of Andh ra Pradesh. METHODS. As part of a population-based epidemiologic study, the And hra Pradesh Eye Disease Study (APEDS), a 16-item visual function questionnaire was designed and applied to 7363 persons older than 15 years, to record the leve ls of difficulty perceived by the subjects. Of these, 123 persons were found to have low vision. Rasch analysis was used to convert the ordinal difficulty ratin gs of these 123 persons into interval measures of perceived visual ability for f unctional vision. RESULTS. Content validity of the questionnaire was demonstrate d by good separation indices (3.17 and 5.44) and high reliability scores (0.91 a nd 0.97) for person and item parameters. Construct validity was shown with model fit statistics. Criterion validity of the questionnaire was shown by good discr imination among the general vision ratings. The functional situation that requir ed the least visual ability was "reaching an object farther or closer than you thought"; the situation requiring the most visual ability was"recognizing smal l objects."Bivariate regression analysis determined that for every unit of logM AR visual acuity, perceived visual ability for functional vision decreased by 2. 9 logit, which could explain 32%of the variability in the person measure. CONCL USIONS. The described assessment, across a range of visual problems, is a valid way to measure perceived ability for functional vision in persons with low visio n. Perceived visual ability varies with every unit of logarithm of the minimum a ngle of resolution (logMAR) visual acuity.
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