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Sina Farsiu, Rachelle V. O’Connell, Stephanie J. Chiu, Katrina P. Winter, Laura A. Clark, Du Tran-Viet, A2A SDOCT Study Group, Joseph A. Izatt, Cynthia A. Toth; Comprehensive Atlas of RPE-Drusen Complex Thickness Maps for Classification of Eyes with and without Intermediate AMD. Invest. Ophthalmol. Vis. Sci. 2012;53(14):844.
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To quantify the normal range and topography of the RPE+drusen complex (RPEDC), consisting of the axial distance of the RPE layer’s apex to Bruch’s membrane, as seen on SDOCT. To utilize RPEDC as a quantitative indicator of AMD status.
We developed DOCTRAP software to semi-automatically measure RPEDC thickness maps in one eye of 118 elderly non-AMD subjects (e.g. Fig.1A) and 256 subjects with intermediate AMD (e.g. Fig.1B&C) from the AREDS2 Ancillary SDOCT Study (ClinicalTrials.gov #: NCT00734487). We interpolated the maps to achieve comparable resolution and registered all normal RPEDC maps to estimate the average normal map (Fig.1D) and its variance (Fig.1F). We deemed RPEDC thicknesses larger or smaller than mean±3×standard deviation as abnormal, i.e. indicative of drusen and geographic atrophy (GA), respectively. In a 5mm diameter cylinder centered at the fovea of each eye, we measured the total RPEDC volume and evaluated the volumes of abnormal RPEDC thickening or thinning by region.
RPEDC was thickest at 0.5mm distance from the fovea in control eyes (Fig.1D). Abnormally thickened RPEDC was more frequent near the fovea (Fig1.H). The RPEDC thickness was on average significantly higher in the AMD eyes compared to control eyes (e.g. 42 vs. 30um in a 1.5mm radius from the fovea, p<0.0001). However, the most efficient method for separating AMD and control eyes was to utilize the volumes of abnormal thickening and thinning of RPEDC as the distinguishing factor (Fig. 1.G-K).
RPEDC volume alone does not efficiently differentiate eyes with intermediate AMD from normal eyes. Analyzing the topographic distribution of normal and abnormal RPEDC thicknesses across a large atlas of eyes allowed us to identify and validate quantitative factors to distinguish AMD from normal. The subsequent quantitative measure based on the volumes of pathologically thickened and thinned RPEDC is powerful for classification of eyes into normal and intermediate AMD categories.
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