Abstract
Purpose :
The retinal pigment epithelium (RPE) is susceptible to regional atrophy in several retinal degenerative diseases, such as age-related macular degeneration (AMD). Variations of RPE phenotype and function with retinal location influence the development of Geographic Atrophy, a late stage of AMD. Understanding the precise location and the nature of RPE phenotypic and molecular differences will be invaluable to study retinal diseases. In this work, we provide a detailed and comprehensive morphometric map of the entire human RPE and show how it changes in AMD.
Methods :
RPE/choroid flatmounts were generated from more than 20 human non-AMD and AMD eyes. The entire flatmounts were stained for RPE cell borders and imaged. An open-source software for image analysis, based on machine learning, was developed to quantify RPE morphometry. Spreadsheets with raw data and heatmaps were generated to compare regional RPE differences.
Results :
RPE cell area analysis of non-AMD eyes revealed the presence of 5 statistically different subpopulations, which we named as P1 to P5. P1 corresponded to fovea and parafovea (median: 147.2 ± 15.4 µm2 sd), while P5 corresponded to far-peripheral RPE (median: 331.9 ± 27.2 µm2 sd). Interestingly, a peripheral ring of smaller RPE cells (P4) was discovered (median: 176.8 ± 18.7 µm2 sd) that is closer in size to perifoveal RPE cells (median: 177.6 ± 15.7 µm2 sd). RPE aspect ratio increased gradually with retinal eccentricity, while hexagonality decreased correspondingly. The morphometric differences between RPE subpopulations, seen in non-AMD eyes, decreased in AMD eyes. Each subpopulation had greater variability compared to non-AMD (30-70% higher standard deviation). Analysis of RPE atrophies in AMD eyes and ultra-widefield retinal images of patients with Late-Onset Retinal Degeneration (L-ORD) and Choroideremia (CHM) showed that P1, P4 and P5 were most affected in AMD, while mid-peripheral subpopulation P3 was the most affected in L-ORD and CHM.
Conclusions :
Overall, the study provides the first exhaustive morphometric map of the human RPE and a geographic reference of RPE subpopulations for future studies. The analysis of AMD eyes will help to predict disease progression using RPE morphometry progression. Future studies will focus on finding molecular markers for RPE subpopulations to understand the etiology of retinal diseases.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.