Abstract
Purpose:
Previous studies on human RPE morphology determined spatial differences in density: a higher density of RPE cells in the macula region with decreasing density peripherally. The aim of our study was to analyze the normal cell morphometry of the RPE in the human eye using modern computational methods with significant accuracy and objectivity.
Methods:
Cadaveric non-diseased human donor eyes (n=3) harvested less than 6h postmortem were microdissected to obtain a strip of RPE from the optic nerve along the macula to the ora. The RPE was flatmounted, stained with AF635-phalloidin and propidium iodide, then imaged by confocal microscopy. Images were photomerged using Photoshop CS2, then analyzed for parameters such as cell density and area, eccentricity, form factor, and topology, using ImageJ (NIH) and CellProfiler software (Broad Institute, MA). The methods used in this study allow reproducible, clear and consistent analysis of RPE cells.
Results:
Cell density was consistently significantly higher at the macula compared to the periphery (p<0.05), with a marked change close to the periphery. RPE cells in the macular region were found to have a very regular, predominantly hexagonal array, with the RPE maintaining this structure in the mid-periphery despite increasing cell size. The far periphery showed marked irregularity in RPE cell shape and size, and the difference from macula to periphery was significant for all three measures (p<0.05), based on measurements of eccentricity, form factor and topology. For all three eyes a clear trend was seen from the macula to periphery, which was found to be significant for all parameters.
Conclusions:
A progressive change in the morphology of the RPE cells can clearly be seen from the macula to the periphery. The higher density of RPE cells in the macular region may be necessary to support the requirements of the retina and increased cone density. A sudden increase in cell size and eccentricity was seen at the periphery, suggesting a different environment and/or function. Further research includes a larger sample size, and the use of computer modeling to look at tension forces, to better understand changes at the periphery compared to the macular region. Understanding normal RPE morphology will help to better recognize and understand RPE morphology in pathologic conditions.
Keywords: 701 retinal pigment epithelium