Measuring geographic atrophy in advanced age-related macular degeneration

PURPOSE. To present a method developed for measuring areas of geographic at rophy (GA) in advanced age-related macular degeneration. METHODS. A microfilm reader projected the 30 degrees fundus photograph of t he macula. Retinal landmarks, atrophic areas, and spared areas within the a trophy were traced, without access to drawings of other years. The total at rophic area was calculated, as was the atrophy within a four-disc-area circ le centered on the estimated foveal center. The configuration of the atroph y was documented. RESULTS. Avoidable sources of discrepancy included variability in peripapil lary atrophy seen on the photograph, and variability seen in the extent of the field. Reproducibility studies found a median absolute difference of 0. 19 Macular Photocoagulation Study disc areas (DA) in total atrophy between repeat drawings, with 75% of repeat drawings having a difference of less th an 0.33 DA. For central atrophy measures, there was a median difference of 0.08 DA, with 75% of pairs having a difference of less than 0.18 DA. Featur es making the definition of borders of GA difficult include the presence of drusen and pigmentary alteration, a fundus in which choroidal vessels are easily visible, and variation in the appearance of GA within a single area of atrophy. CONCLUSIONS. This method provides a reliable means of measuring the size of atrophic areas in GA and will be useful for measuring longitudinal change. It may be difficult to determine whether central spared areas are present, and correlation with visual acuity and macular perimetry may be helpful.