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Retinal pigment epithelial abnormalities in fundus flavimaculatus: a light and electron microscopic study.

Light, fluorescent, and scanning and transmission electron microscopic examinations of two postmortem eyes from a 24-year-old man with well-documented fundus flavimaculatus with atrophic macular degeneration revealed striking abnormalities in the retinal pigment epithelium (RPE). Beginning near the equator, scanning electron microscopy demonstrated a progressively marked heterogeneity in the size of the RPE cells. Surrounded by a fairly regular mosaic of relatively normal appearing cells, enormously enlarged hypomelanotic cells measuring up to 80 microns in diameter occurred in irregular aggregates that became more prevalent posteriorly. Diffusely and intensely PAS-positive, the RPE was packed with a granular substance with ultrastructural, autofluorescent, and histochemical properties consistent with an abnormal form of lipofuscin. The greatest concentration of lipopigment was noted posteriorly. Stains for acid mucopolysaccharide were only mildly positive. The clinical and fluorescein angiographic manifestations of fundus flavimaculatus are consistent with accumulation of a lipofuscin-like substance in the RPE. The massive amounts of lipopigment encountered in this young individual suggest that disordered lipopigment metabolism may play a major role in the pathogenesis of this retinal pigment epithelial disorder.