Outer Retinal Thickness and Fundus Autofluorescence in Geographic Atrophy

Abstract

Most studies of fundus autofluorescence (FAF) in geographic atrophy (GA) have been nonquantitative, with inadequate registration of image modalities. Furthermore, as pointed out in the recent Consensus Definition for Atrophy Associated with Age-Related Macular Degeneration on OCT, it is unclear whether decreased FAF would be correlated exclusively with a single category of OCT-defined atrophy. We sought to determine how FAF intensity in eyes with GA correlates with structural changes of the outer retina and choroid as seen on co-registered spectral domain OCT (SD-OCT) images. Retrospective cross-sectional. Twenty eyes of 11 patients with GA secondary to non-neovascular age-related macular degeneration (AMD). Spectral domain OCT and FAF images for each eye were co-registered using MATLAB (MathWorks Inc, Natick, MA). On B-scans, the choroid, retinal pigment epithelium (RPE), photoreceptor (PR) layer, and outer nuclear layer (ONL) were segmented. Regions of interest (ROIs) including all atrophic and border regions were selected manually on the FAF scans. Regions of interest were subdivided into quartiles of FAF level to correlate with retinal thickness measurements taken along the B-scans. Mean choroid, RPE, PR, and ONL thicknesses were compared across quartiles using an analysis of variance factorial design testing for interaction effects, adjusted for repeated measures (on both eyes) with a within-subjects factor. Seventeen eyes of 10 patients were selected for analysis. The mean choroidal thicknesses were not significantly different across FAF quartiles, but the overall differences in mean RPE, PR layer, and ONL thicknesses across quartiles were statistically significant (analysis of variance, P < 0.001, P < 0.001, and P=0.015, respectively). Post hoc analysis demonstrated significant differences in thickness among quartiles 1, 2, and 3 for the RPE and PR layers (Tukey, P < 0.01 in each case). The FAF quartiles within GA did not correlate exclusively with single categories of Consensus Definition for Atrophy Associated with Age-Related Macular Degeneration-defined atrophy. Not only RPE but also PR layer thickness on SD-OCT varies significantly with FAF levels in GA. This suggests that although the RPE cells are losing thickness and function, evidenced by decreased FAF from fluorophores, delicate PR cells also succumb early in the disease process. These relationships should be pursued as a possibly better-detailed mechanism in GA.