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Intersession repeatability of visual acuity scores in age-related macular degeneration.

PURPOSE
To describe the intersession repeatability of visual acuity measures obtained with Early Treatment of Diabetic Retinopathy Study (ETDRS) charts in patients with age-related macular degeneration.


METHODS
Visual acuity was measured in four sessions over 12 weeks using a standardized protocol with ETDRS charts in 107 nontreated eyes of 107 patients with age-related macular degeneration enrolled in an ongoing clinical trial.


RESULTS
Data from 90 patients were included in the analysis. The 95% coefficient of repeatability (CR) was 12 ETDRS letters and ranged from 9 letters for 29 eyes with small to intermediate drusen only to 17 letters for 25 eyes with late AMD (macular scars or geographic atrophy). Ten (11%) eyes had a 5-letter reduction or more in visual acuity at the week 1 visit compared with baseline. Excluding seven eyes with visual acuity measurements potentially affected by measurement-related factors (a change in testing distance between visits) the revised CR was 10 letters for the cohort (n = 83) and 11 letters for the late-AMD subgroup (n = 18).


CONCLUSIONS
Intersession ETDRS visual acuity measurements are subject to considerable variability in patients with AMD. The variability may be due to both measurement- and disease-related factors. The variable readings have implications for AMD clinical trial design and for the assessment and treatment of patients with neovascular AMD. Further work is needed to determine both the sources of variability in visual acuity measurements and the optimal change criterion for visual acuity measurements in this important group of patients.