SHIFTING RELATIONSHIPS BETWEEN PHOTORECEPTORS AND PIGMENT EPITHELIAL-CELLS IN MONKEY RETINA - IMPLICATIONS FOR THE DEVELOPMENT OF RETINAL TOPOGRAPHY

This study examines the spatiotemporal relationships between retinal p igment epithelium (RPE) and photoreceptors (PR) during development of Macaca nemestrina retina. Our aim was to learn more about the developm ental dynamics of these two important cell populations, particularly w hether developmental changes in RPE cell densities mimic those of PR a t selected retinal points. Twelve eyes ranging in age from 100 fetal d ays (Fd) to adulthood were flatmounted; the retinal perimeters were tr aced; and then sample punches were taken of the RPE and neural retina at the fovea, optic disc, mid- and far-nasal periphery, and far tempor al, inferior and superior periphery. The two tissues were gently separ ated and the RPE cells and photoreceptors from the same region of the punch were counted using Nomarski contrast interference optics. We fou nd that the total number of cones remains stable around 4 million betw een Fd100 and adulthood, but RPE number increases from 1.6 million at Fd100 to 2.56 million in adulthood. At the fovea, the core:RPE ratio i ncreases from 5.4:1 at Fd100 to 28:1 by adulthood. In the temporal per iphery by contrast, the cone:RPE ratio declines from 2.2:1 at Fd100-11 0 to less than I:1 in the adult. In the vicinity of the optic disc, th e ratio of (cones + rods): RPE remains around 35:1 throughout developm ent, but in the retinal periphery it decreases to the adult value of 2 2:1. These changing ratios indicate that photoreceptors and RPE cells are redistributed independently during development, and that these two cellular sheets slide over one another to achieve their final distrib ution. This situation suggests that the forces or factors causing fove ation are intrinsic to the neural retina.