Low luminance visual dysfunction as a predictor of subsequent visual acuity loss from geographic atrophy in age-related macular degeneration.

OBJECTIVE: To show that low luminance visual dysfunction is predictive of subsequent visual acuity (VA) loss in eyes with geographic atrophy (GA) resulting from age-related macular degeneration (AMD).
DESIGN: Cohort study examining the prospective natural history study of GA from 1992 through 2000 at the Wilmer Eye Institute. PARTICIPANTS: Ninety-one participants with GA resulting from AMD without choroidal neovascularization in at least 1 eye who completed a 2-year study examination.
METHODS: Annual examinations included measurement of best-corrected VA, low luminance VA, Pelli-Robson contrast sensitivity, reading speed, examination, and fundus photography. The total GA area was quantified, as was the GA within a 10.2-mm(2) circle centered on the fovea. MAIN OUTCOME MEASURES: Visual acuity loss at 2 years and risk factors for visual loss.
RESULTS: Participants with baseline VA of 20/50 or more had a 40% 2-year rate of VA loss of 3 lines or more, compared with 13% for the participants with worse baseline acuities. The baseline low-luminance deficit (LLD) in VA was a strong predictor of subsequent VA loss for all levels of baseline VA. Within the good baseline VA group, the relative risk (RR) of 3-line loss for the worse LLD group compared with the better LLD group was 2.88 (95% confidence interval [CI], 1.13-7.35). The LLD is a stable and reproducible measure. Other significant visual function predictors of subsequent VA loss in eyes with good baseline VA included foveal dark-adapted sensitivity (RR, 4.20; 95% CI, 1.39-12.71) and reduced reading rate (RR, 2.43; 95% CI, 1.11-5.31). The rate of VA loss within the good acuity group was higher when the GA included 25% to 75% of the central 10.2 mm(2) than in eyes with GA including less than 25% or more than 75% of the central 10.2 mm(2). The following were not significant predictors of subsequent VA loss among these participants: age, gender, fellow eye diagnosis, fellow eye VA, baseline GA area, and GA enlargement rate.
CONCLUSIONS: Visual function measures can predict the risk of future VA loss in subjects with GA and good baseline VA. They may allow identification of the highest risk group for VA loss, enabling more efficient design of clinical trials. They also may be appropriate surrogate measures of foveal health in short-term treatment trials.