Pattern-related visual stress, chromaticity, and accommodation.

PURPOSE: To investigate the impact of colored overlays on the accommodative response of individuals, with and without pattern-related visual stress (PRVS), a condition in which individuals manifest symptoms of perceptual distortion and discomfort when viewing a 3-cyc/deg square-wave grating. METHODS: Under double-masked conditions, 11 individuals who reported PRVS selected an overlay with a color individually chosen to reduce perceptual distortion of text and maximize comfort (PRVS group). Two groups of control subjects individually matched for age, sex, and refractive error were recruited. Control group 1 similarly chose an overlay to maximize comfort. Control group 2 used the same overlays as the paired PRVS participant. The overlay improved reading speed by 10% (P < 0.001), but only in the PRVS group. A remote eccentric photorefractor was used to record accommodative lag while participants viewed a cross on a background. The background was uniform or contained a grating and was either gray or had a chromaticity identical with that of the chosen overlay. There were therefore four backgrounds in all. RESULTS: Overall, the accommodative lag was 0.44 D greater in the participants with PRVS. When the background had the chosen chromaticity, the accommodative lag was reduced by an average of 0.16 D (P = 0.03) in the PRVS group, but not in the symptom-free groups: in control group 2 the colored background slightly increased the accommodative lag. CONCLUSIONS: Accommodative lag was greater in individuals susceptible to pattern-related visual stress and was reduced by a colored background.

Assessing visual activities of daily living in the visually impaired.

PURPOSE: Visual function assessment questionnaires ask people to rate the difficulty they have performing visual activities of daily living (ADLs). This study examines the relationship between self-reported difficulty and actual performance in such ADLs. METHODS: Twenty four subjects with established bilateral visual impairment initially self-reported their difficulty with 4 ADLs (reading newsprint, reading medicine labels, identifying coins and entering a PIN). Subjects' performance in variants of these ADLs was then assessed by measuring the time taken; by an observer rating subjects' performance; and by the subject rating their perceived difficulty with each specific task. Clinical visual function parameters were also assessed. RESULTS: Varying the assessed ADL task changed how well the task correlated with self-reported difficulty. Clinical visual function, rate of task completion and observer rating of difficulty all correlated significantly with self-reported difficulty, explaining up to 69% of the variance in self-reported difficulty. However, despite replicating the ADLs as closely as possible in the clinical environment the perceived difficulty of the clinic tasks was rated as being less than the initial self-reported difficulty of the real-world task. CONCLUSIONS: The task variant used is important when assessing functional visual performance directly. Timed and observer-rated methods of assessment can be appropriate for assessing functional vision. In this small study, the disconnect between self-reported visual difficulty and perceived or assessed difficulty suggests that functional performance is not the only factor influencing self-report, and responses to visual function assessment questionnaires should be interpreted in this light.