Morphological Characteristics and Clinical Comparison of Autofluorescence and Polarization-Sensitive Optical Coherence Tomography in Geographic Atrophy

Abstract

Purpose: : Geographic atrophy (GA) is often associated with subtle but proceeding loss of central visual function due to progressing atrophy of the retinal pigment epithelium (RPE) and photoreceptors. Autofluorescence imaging (AF) is commonly used to image GA. Various patterns have been identified and correlated to progression of this disease. Since classification and interpretation of GA in AF is often difficult and compromised by subjective influences, a study was performed to compare the characteristics of AF measurements in GA to polarization sensitive spectral domain optical coherence tomography (PS-SD-OCT) imaging capable to map the RPE in an automated process.

Methods: : 50 eyes of 40 patients representing the entire spectrum of GA patterns in AF were examined in a prospective observational case series. A PS-SD-OCT capable of measuring the degree of polarization uniformity (DOPU) in retinal tissue was used in comparison to Spectralis (Heidelberg Engineering), Cirrus SD-OCT (Carl Zeiss Meditec) and Topcon OCT devices in all patients. Based on the unique property of the RPE to depolarize backscattered light, retinal thickness and RPE integrity maps were generated out of PS-SD-OCT datasets and compared to conventional SD-OCT findings and AF measurements performed with the Spectralis OCT. PS-SD-OCT data was then correlated to AF and conventional SD-OCT imaging.

Results: : Unlike the regular appearance, which can be found in the RPE in healthy eyes, PS-SD-OCT identified the central RPE-atrophy and irregular patterns of elevated RPE at the margins of the atrophic zones. Elevations in the pattern of the RPE could be visualized in automatically generated elevation and summation maps of the degree of polarization uniformity (DOPU). Three-dimensional models allowed correlating discrete changes in the intraretinal morphology with changes in the DOPU images. The hyperfluorescent margins frequently present in AF images of GA correlated with inhomogenous elevations and thickening of the RPE in DOPU images.

Conclusions: : AF and PS-SD-OCT measurements both revealed the size of GA consistently. Hyperfluorescent marginal zones, often associated with progression of the disease could be compared to PS-SD-OCT findings and showed an inhomogenous appearance, indicating that summation effects present in AF imaging might obscure relevant morphological features at the level of the RPE.

Keywords: age-related macular degeneration • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retinal pigment epithelium