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Ronald P. Danis, Amitha Domalpally, Larry D. Hubbard, Ashwini Narkar, James White, Emily Y. Chew, Traci E. Clemons; Index of Non-Circularity of Areas of Geographic Atrophy (GA) Is Related to Progression Rate. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2054.
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We evaluated a parameter based upon an indirect measure of the extent to which the shape of an area of GA in an eye departs from that of a circle as a risk factor for rate of GA expansion in a sample of AREDS eyes.
Among 181 eyes in AREDS that had incident or baseline GA and with 4 years of follow up, the perimeter and area of GA was measured from digitized color photographs using planimetry. A Non-Circularity Index (NCI) was calculated based upon the ratio of the measured area of GA (actual area) to the area of GA expected for a given perimeter (expected area) NCI = actual area/expected area; range 0.0 to 1.0; a value of 1.0 indicates a circular shape and departure from 1.0 indicates non circularity or an irregular shape. Progression rates of eyes with 4 years of follow up were associated with baseline NCI and GA area.
Of 106 eyes with 4 years follow up, the median NCI was 0.5 and the distribution of baseline NCI was roughly equal between the groups 0-0.25, 0.26-0.50, 0.51-0.75, and 0.76-1.0. The 4 year median progression rates were 2.55, 1.76, 1.52, and 0.58 mm2/yr for these NCI categories respectively (p<0.001 ANOVA).
NCI was strongly associated with progression rate of GA and may be a useful predictor for use in clinical trial eligibility. This association also suggests that future rate of enlargement of GA in an eye may be more related to the junctional zone of RPE at risk rather than simply to area of GA.
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