Surface morphology of explants from the human retinal pigment epithelium in culture. A scanning electron microscopic study.

The alterations in surface morphology in human retinal pigment epithelium in explant culture was studied by scanning electron microscopy. After 14 days in culture, large areas of the epithelium showed well preserved surface villi. In some zones, however, the density of the finger-like villi were reduced and the shorter villi became more visible. The short villi are lamellar in structure and constitute systems of communicating membranous folds and not isolated structures as previously believed. Most of the tall finger-like villi were found to have their bases on the top of these folds. Dead cells followed 2 different pathways of degeneration. Some showed large ruptures in the membrane, followed by expulsion of organelles and finally detachment of the cell from Bruch's membrane. With other cells, a progressive disintegration of the cell membrane was observed. The first type of degeneration occurred most frequently in dilated, single cells, whereas the latter type was found in larger areas of necrosis.