Abstract
Purpose :
Organelles acquired in RPE cells over time, lipofuscin (LF) and melanolipofuscin (MLF), are primary signal sources for clinical AF. AMD tissue microscopy can elucidate the subcellular basis of AF imaging. In donor AMD eyes we defined and characterized phenotypes of RPE morphology and AF and analyzed frequencies and associations of these phenotypes.
Methods :
We analyzed images from 25 RPE-Bruch’s membrane flatmounts of 25 donors with AMD. To visualize LF/MLF granules and phalloidin-labeled actin cytoskeleton, a wide-field epi-fluorescence microscope created 0.4 μm apical-to-basal z-stack images. Using a custom ImageJ plugin, we classified >18,000 RPE cells, selected in a systematic unbiased fashion, for morphology and AF pattern. Phenotypes were pooled into categories of increasing pathology (Table). For each cell, area, AF intensity and number of neighboring cells (NN, derived from Voronoi diagrams) were analyzed. In all phenotypes, these parameters were compared to Phenotype 1 via generalized estimating equations. We used each cell as a reference to analyze characteristics of its immediate neighborhood (adjacent Voronoi regions).
Results :
Compared to Phenotype 1 (healthy), all other phenotypes (diseased) differed significantly in area (p=0.0324), AF (p=0.0009) and NN (p=0.0024). Phenotypes 1 and 6 had the smallest and largest area, respectively. Phenotypes 2 and 5 had the lowest AF. No phenotypes were significantly brighter than Phenotype 1. Phenotypes 6 and 2 had the most and fewest NN, respectively. Phenotype 1 was the most frequent neighbor for all phenotypes, but decreased with increasing reference cell pathology. Neighbor frequency distribution was more variable with increasing pathology. Neighborhood mean cell area increased with increasing pathology. Neighborhood mean cell AF was lower in Phenotypes 2 and 5.
Conclusions :
We quantified frequency of RPE phenotypes in a systematic unbiased sample of AMD tissues. As AMD progresses, RPE cells enlarge; AF intensity shows little consistent change. Data support evidence from clinical quantitative AF imaging that AMD eyes exhibit overall low rather than high AF, and that focal high AF is due to vertical superimposition of migrated or stacked cells not seen in flat mounts.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.