Relationship of Topographic Distribution of Geographic Atrophy to Visual Acuity in Nonexudative Age-Related Macular Degeneration

PURPOSE To investigate the topographic distribution of geographic atrophy (GA) and to identify a continuous anatomic endpoint that correlates with visual acuity (VA) in eyes with GA. DESIGN Retrospective analysis of a multicenter, prospective, randomized controlled trial. PARTICIPANTS The Age-Related Eye Disease Study (AREDS) participants with GA secondary to nonexudative age-related macular degeneration. METHODS We manually delineated GA on 1654 fundus photographs of 365 eyes. We measured GA areas in 9 macular subfields in Early Treatment for Diabetic Retinopathy Study (ETDRS) grid and correlated them with VA via a mixed-effects model. We determined the optimal diameter for the central zone by varying the diameter from 0 to 10 mm until the highest r2 between GA area in the central zone and VA was achieved. We estimated the VA decline rate over 8 years using a linear mixed model. MAIN OUTCOME MEASURES GA area in macular subfields and VA. RESULTS The percentage of area affected by GA declined as a function of retinal eccentricity. GA area was higher in the temporal than nasal region (1.30 ± 1.75 vs. 1.10 ± 1.62 mm2; P = 0.005), and in the superior than inferior region (1.26 ± 1.73 vs. 1.03 ± 1.53 mm2; P < 0.001). Total GA area correlated poorly with VA (r2 = 0.07). Among GA areas in 9 subfields, only GA area in the central zone was independently associated with VA (P < 0.001). We determined 1 mm as the optimal diameter for the central zone, in which GA area correlated best with VA (r2 = 0.45). On average, full GA coverage of the central 1-mm-diameter zone corresponded to 34.8 ETDRS letters decline in VA. The VA decline rate was comparable between eyes with initial noncentral and central GA before GA covered the entire central 1-mm-diameter zone (2.7 vs. 2.8 ETDRS letters/year; P = 0.94). CONCLUSIONS The prevalence of GA varies significantly across different macular regions. Although total GA area was poorly associated with VA, GA area in the central 1-mm-diameter zone was significantly correlated with VA and may serve as a surrogate endpoint in clinical trials.