Maturation of newly-formed subretinal vessels.

The maturation process of newly-formed subretinal vessels was studied ultrastructurally. Primitive new vessels have thick endothelial cells with cytoplasm that contains many ribosomes and rough endoplasmic reticulum. Some immature endothelial cells show budding, and many of the intercellular junctions have small gaps. As the newly-formed vessels mature, the endothelial cells become attenuated and fenestrated, and their junctions become tight. Mature subretinal new vessels closely resemble those of the normal choriocapillaris.