OCT Measurements of the Retinal Pigment Epithelium to Bruch's Membrane Thickness around Geographic Atrophy Correlate with Growth: Short title: Thickened RPE/BM complex predicts faster GA growth.

PURPOSE The retinal pigment epithelium (RPE) to Bruch's membrane (BM) distance around geographic atrophy (GA) was measured using an optical attenuation coefficient (OAC) algorithm to determine if this measurement could serve as a clinical biomarker to predict the annual square root enlargement rate (ER) of GA. DESIGN A retrospective analysis of a prospective, observational case series. METHODS Eyes with GA secondary to age-related macular degeneration (AMD) were imaged with swept-source OCT (SS-OCT) using a 6 × 6 mm scan pattern. GA lesions were identified and measured using customized en face OCT images, and GA annual square root ERs were calculated. At baseline, the OACs were calculated from OCT datasets to generate customized en face OAC images for GA visualization. RPE-BM distances were measured using OAC data from different sub-regions around the GA. RESULTS A total of 38 eyes from 27 subjects were included in this study. Measured RPE-BM distances were the highest in the region closest to GA. The RPE-BM distances immediately around the GA were significantly correlated with GA annual square root ERs (r = 0.595, p<0.001 for a 0-300 µm rim around the GA). No correlations were found between RPE-BM distances and previously published CC flow deficits in any sub-regions. CONCLUSIONS RPE-BM distances from regions around the GA significantly correlate with the annual ERs of GA. These results suggest that an abnormally thickened RPE/BM complex contributes to GA growth and this effect is independent of CC perfusion deficits.