Comparing Fundus Autofluorescence and Outer Retinal Thickness on Optical Coherence Tomography in Geographic Atrophy (GA)

Abstract

Purpose : Changes in the outer retina and choriocapillaris¹ have shown to precede the development of RPE atrophy seen on fundus autofluorescence (FAF) in GA. The purpose of our study is to determine whether patterns of FAF in eyes with geographic atrophy (GA) correlate with structural changes seen on spectral domain optical coherence tomography (SD-OCT).

Methods : SD-OCT and FAF images of 8 eyes of 5 patients with GA and RMD were obtained. SD-OCT b-scans through areas of GA were selected for analysis. Using a Matlab program, the choroid, retinal pigment epithelium (RPE), photoreceptor (PR) layer, and outer nuclear layer (ONL) were segmented and thicknesses of each layer were calculated. FAF images co-registered with OCT en face images. Gray level intensities of GA regions on FAF were analyzed using quartile analysis¹. Mean choroid, RPE, PR, and ONL thicknesses were compared across quartiles using one-way ANOVA.

Results : The mean choroid, RPE, and ONL thicknesses were not significantly different across FAF quartiles of the 8 eyes (p<0.99, p<0.08, and p<0.13, respectively). The difference in mean PR thickness across quartiles was statistically significant (p<.001). The mean PR thickness was 115.9 microns in the first quartile, 169.6 microns in the second quartile, 197.8 microns in the third quartile, and 215.0 microns in the fourth quartile.

Conclusions : Photoreceptor layer thickness on SD-OCT varies significantly with FAF levels in GA, while other outer layer thicknesses do not. This suggests that the PRs are most delicate and physically succumb first; the RPE physically may not lose thickness yet, but is already losing FAF and presumably also function. Underlying this is loss of choriocapillaris perfusion¹. These relationships should be pursued as a possibly better detailed mechanism in GA. 1. Sacconi et al, Retina, 2017. 2. Agee et al, IOVS, 2017.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Figure 1: SD-OCT b-scan (top) and corresponding FAF quartile map (bottom). OCT segmentation lines represent the choroidal/scleral interface (teal), outer border RPE (red), inner border RPE (orange), ELM (violet), and inner border ONL (green). On the FAF map, the first quartile is represented in dark blue, second quartile in light blue, third quartile in green, and fourth quartile in yellow. Outliers (upper and lower 2.5% of intensities) are shown in white. The small central GA on OCT has very low AF, and shows near total loss of PRs.