Purpose: To determine the degree of concordance for progression rate, size of atrophy, and visual acuity in patients with bilateral geographic atrophy (GA) due to age-related macular degeneration (AMD).
Methods: Analysis was performed in 156 eyes of 78 patients with bilateral GA. Best corrected visual acuity was determined with ETDRS charts. GA was quantified in digital fundus autofluorescence images (excitation, 488 nm; emission, >500 nm) by semiautomated imaging analysis. A linear, two-level, random-effects model was used to assess the natural course of disease. The concordance correlation coefficient (CCC) was calculated to assess the degree of agreement between disease characteristics of the left and right eyes. Bland-Altman plots were applied to compare measurements in the eyes.
Results: CCC between the eyes was 0.310 (95% CI, 0.097-0.495) for visual acuity, 0.706 (95% CI, 0.575-0.801) for GA size, and 0.756 (95% CI, 0.644-0.837) for GA progression rate. Although Bland-Altman plots revealed high concordance for the progression rate, there was considerable discrepancy between both eyes for GA size. [corrected]
Conclusions: GA progression in bilateral atrophic AMD is a symmetrical process; however, GA size may differ substantially between the eyes. High concordance in intraindividual disease progression in the presence of a high degree of interindividual variability indicates an influence by genetic and/or environmental factors rather than nonspecific ageing changes. The relatively small concordance of GA size in this cohort may indicate asymmetric evolution of the disease in affected individuals. The results may be useful in the design of future clinical trials designed to slow the rate of GA progression (Clinical Trials.gov number, NCT00393692).