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Carol A Applegate, Janet S Sunness; Circularity Index and other morphologic features as risk factors for the progression of geographic atrophy (GA) from AMD. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2852.
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© ARVO (1962-2015); The Authors (2016-present)
A recent study from AREDS showed that areas of GA that were less circular had a lower more rapid growth rate. The data from the NIH-funded prospective natural history study of GA conducted at Wilmer from 1992 to 2000 were reanalyzed to determine whether the circularity index or other morphologic features were risk factors for more rapid progression in this population.
Annual fundus photographs for the study, and drawings were made of the areas of GA and of spared areas as described previously. Drawings with macular GA contiguous with peripapillary GA were excluded, as were drawings with atrophy that extended to the edge of the photographic field. The study population after this included 766 drawings of 188 eyes with GA of 118 subjects. Using Photoshop CC, the areas of atrophy were selected and the perimeters and areas were measured. The circularity index (GACI) was calculated as the ratio of the actual area to the area calculated from radius=perimeter divided by 2 pi, i.e. assuming it is a circle.
The mean (sd) square root baseline area was 2.59 (1.16) mm, baseline area was 8.10 (6.75) square mm, and enlargement rate was 0.34 (0.22) mm/year. For univariate analysis, the following was found. Circularity: Analyzed continuously, the enlargement rate decreased by 0.024 for every additional 0.1 of circularity. Stratified, the enlargement rate for GACI>0.75 was 0.24, and was significantly different from GACI<0.25 (0.38) and GACI between 0.25 and 0.75 (0.36). Configuration: Multifocal and horseshoe had significantly greater enlargement rates than solid lesions. Number of areas: Eyes with 1 area had a significantly lower enlargement rate than eyes with 2 or more areas (1 area 0.30, 2 or more 0.40, p=0.0012). Fellow eye status: Bilateral GA eyes had lower enlargement rates than fellow eye drusen eyes (bilat 0.32, dru 0.44, fell eye CNV 0.36). The square root baseline area did not have a significant effect on enlargement rate. Multivariate analysis showed that only GA configuration was significant (F=15.40, p<0.001) when the factors listed above were included.
Configuration of GA has a significant effect on enlargement rate. Circularity index shows that the most circular areas (GACI >0.75) progress most slowly. These data may be useful in determining eyes at high risk for more rapid enlargement of GA.
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