Explants of human retinal pigment epithelium were maintained in culture in various types of media, and examined by light and transmission electron microscopy. After one month in vitro, the central areas showed a monolayered configuration with distinct polarity and presence of ruthenium red stainable material on the apical surface. On the peripheral areas of Bruch's membrane, multilayered lesions were observed to develop and to extend from the monolayered epithelium and past the cut edge in Bruch's membrane. Cells in these lesions contained little melanin and generally lacked an apico-basal polarity. Ruthenium red staining revealed the presence of electron dense material on the apical surface of the lesions as well as in the extracellular space between cells in the various layers. Development of multilayered lesions with deposition of extracellular material are seen in various chorio-retinal disorders, including senile macular degenerations and also subsequent to laser and cryo-therapy. The findings in the present study point to the explant culture system as a valuable tool in the study of important aspects of chorio-retinal pathology.

Cells from samples of human choroidal tissue were collected and seeded onto isolated Bruch's membrane in vitro, and the morphology of the developing cultures was examined by light-, scanning electron- and transmission electron-microscopy. In early cultures, the cells showed a flattened, spread out appearance with short surface villi and a low degree of cellular overlapping. After 48 h, a shift towards a more elongated cell form was observed, and one week old cultures were composed of predominantly elongated cells with a pronounced degree of overlapping. In contrast, human retinal pigment epithelial cells seeded onto sheets of Bruch's membrane maintained a spread out epithelial morphology with a varying degree of overlapping throughout the culture period. The present system permits comparative studies on the behavior of choroidal and pigment epithelial cells under controlled conditions. It may serve as an in vitro model for disorders characterized by growth of these cells on Bruch's membrane in vivo.