The enlargement of geographic atrophy over time in age-related macular degeneration

Purpose. To determine the rate of spread of geographic atrophy (GA) and the symmetry between eyes. Methods. Fundus photographs were taken annually in a prospective natural history study of GA. The atrophic areas for each date were drawn without reference to drawings from other dates. The areas of atrophy were digitized, and measured by computer. 74 patients with bilateral GA (148 eyes) had 293 fundus photographs drawn and analyzed. Average age was 79 yr (66 to 90 yr). Results. 1. For the first photo drawn on each eye, the median total area of atrophy was 4.4 da (MPS disc area, 1 da= 1.77 sq mm), with a range of 0.1 to 27.7 da. There was strong correlation (r=.83) betwee 1 an eye and its fellow, and 50% of eyes had areas within 1.1 da of the fellow eye. The size of the area was negatively correlated with visual acuity, but not with age. 2. For the 90 eyes with ≥ 2 sets of photos available, the median rate of spread of GA was 0.73 da/yr. Only 9 eyes had less than 0.1 da/yr enlargement; the remainder had rates ranging from 0.1 to 5 da/yr. The rate tended to increase with increasing size of atrophic area. 25% of the 40 patients with ≥ 2 sets of photos for both eyes had rates that differed by less than 0.13 da/yr between eyes; the median absolute difference in rates between eyes was 0.38 da/yr. 3. For the 50 eyes with ≥ 3 sets of photos, the second interval rate did not correlate simply with the first interval rate, except that the rate tended to decline if the initial rate was high. Conclusions. The median rate of enlargement of GA was 0.73 da/yr, with 90% showing enlargement. GA is symmetric between eyes in the size of the atrophy in 50% of cases, and 25% have high symmetry of rates between eyes.