The impact of visual impairment on objective and subjective measures of physical disability: SEE project

Purpose. Previous epidemiological studies have shown that visual impairment (VI) is associated with self-perceived difficulty performing everyday tasks. However there is little evidence concerning the association of VI and actual performance of those tasks. The purpose of this report is to compare the relationship between VI and self-perceived difficulty to the relationship between VI and objective task performance. Methods. Visual impairment was assessed with a battery of standardized psychophysical tests administered to 2520 participants in the Salisbury Eye Evaluation (SEE) project. Tests included distance acuity, letter contrast sensitivity with and without glare, stereoacuity, and automated visual fields. Selfperceived difficulty was assessed with interviewer-administered questionnaires. Objective task performance was measured for reading, face recognition, measured walk, stair climb, and telephone use. Each performance-based test had a corresponding questionnaire item. Results. Participants who reported difficulty with a task generally performed the task slower than those who reported no difficulty. The differences were substantial for the reading and mobility tasks (45% slower for those who reported difficulty), but smaller for face recognition and telephone use (12% slower). There was good correspondence between predictors of self-perceived task difficulty and slow task performance. For example, distance acuity and stereoacuity were significant predictors of reported difficulty and measured reading speed for fine print. Conclusions. The association between VI and self-perceived disability is similar to that between VI and objective task performance.