Congenital hypertrophy of the retinal pigment epithelium. Electron microscopic and morphometric observations.

Congenital hypertrophy of the retinal pigment epithelium (CHRPE) is a well-circumscribed, flat, pigmented fundus lesion that is stable and generally nonprogressive. Light and electron microscopy and morphometric analysis was used to study a lesion with the clinical characteristics of CHRPE found in an eye enucleated for a posterior segment malignant melanoma. These studies showed that the lesion was composed of tall, maximally pigmented RPE cells that had a density 1.7 times greater than the density of the adjacent normal peripheral RPE. These observations suggested that cellular hyperplasia and hypertrophy may contribute to CHRPE. Ultraviolet fluorescence microscopy showed no autofluorescent granules of lipofuscin in the CHRPE, suggesting that the lesion's constituent cells lack the capacity to phagocytose and digest photoreceptor outer segments. Photoreceptor degeneration in the overlying retina consequent to this functional defect could be responsible for the localized visual field defects that typically occur in patients with CHRPE.