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Paul F. Stetson, Zohar Yehoshua, Carlos Alexandre A. Garcia Filho, Giovanni Gregori, Philip J. Rosenfeld; Minimum Intensity of OCT A-Scans at the Margins of Geographic Atrophy in AMD. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2047.
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Minimum Intensity (MI) images of OCT A-scans were previously shown to often represent abnormalities in the reflectivity and integrity of the outer nuclear layer and Henle fiber layer. The purpose of this study was to determine if MI can predict the margin of GA that will enlarge.
Patients with GA measuring from 1.25 mm2 to 18mm2 were prospectively enrolled into the COMPLement Inhibition with Eculizumab for the Treatment of Non-Exudative Age-Related Macular Degeneration (COMPLETE) Study. In this study, OCT imaging was acquired at baseline, 12 weeks, and 26 weeks. Two expert graders manually segmented images of GA obtained using OCT (Cirrus™ HD-OCT, Carl Zeiss Meditec Inc.). Baseline scans were compared to the 12- and 26-week follow-up scans, and the 12-week scans were compared to the 26-week scans. Scan coordinates were co-registered using rigid transformation. MI values were studied within a margin of 180 microns around the boundary of GA. MI values in areas with progression of GA were compared using a one-sided t-test with MI values from areas that did not progress.
24 eyes were investigated. Scans from 6 eyes were excluded when registration using rigid transformation resulted in misregistration of more than 100 microns near areas of pathology. When the remaining scans were registered, a statistically significant elevation in MI (p<0.05) was seen in areas of growth in 98/108 comparisons (91%). Over the initial 12 weeks, 92% of the comparisons showed a significantly elevated MI; over the following 14 weeks, 94% of the differences were significant, and over the entire span of 26 weeks, 86% of the differences were significant.
These findings suggest that there is an increase in MI at the margins of GA prior to enlargement. This may indicate disruption of the outer retina in these areas before GA becomes apparent. MI may prove useful as a predictor of enlargement and may be a useful parameter to monitor in eyes with dry AMD undergoing experimental therapies.
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