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Janet S. Sunness, Neil M. Bressler, Yan Tian, Judith Alexander, Carol A. Applegate; Measuring Geographic Atrophy in Advanced Age-Related Macular Degeneration. Invest. Ophthalmol. Vis. Sci. 1999;40(8):1761-1769.
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purpose. To present a method developed for measuring areas of geographic atrophy
(GA) in advanced age-related macular degeneration.
methods. A microfilm reader projected the 30° fundus photograph of the macula.
Retinal landmarks, atrophic areas, and spared areas within the atrophy
were traced, without access to drawings of other years. The total
atrophic area was calculated, as was the atrophy within a
four-disc-area circle centered on the estimated foveal center. The
configuration of the atrophy was documented.
results. Avoidable sources of discrepancy included variability in peripapillary
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 than 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. Features 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
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