Purpose: To describe the cytoarchitecture of the choroidal capillary endothelial cells, especially as it relates to cellular processes that protrude through the basal lamina into Bruch's membrane (BM).
Methods: Human donor eyes and monkey and hamster eyes were examined by transmission electron microscopy and freeze-fracture replication. The number of endothelial cell processes and the characteristics of the processes and surrounding structures were determined in the maculae of human eyes and correlated with age-related changes in neighboring structures.
Results: Endothelial cell processes were observed in eyes of all species examined and at all ages. They typically occurred at sites of focally thickened, nonfenestrated regions of the endothelial cells. The basal lamina adjacent to the processes was often hypertrophic and associated deposits of long-spacing collagen (LSC) were observed frequently. In humans, there was no correlation between the number of processes per 100 micro m of the BM with age, sex, cause of death, postmortem time, RPE autofluorescence, or RPE residual body content. There was a weak linear association with the thickness of the BM.
Conclusions: The finding of cellular processes of choroidal capillary endothelial cells penetrating their basal laminae is normal. These processes may serve to stabilize choroidal endothelial cells physically and play an important structural role in the maintenance of patency of the choriocapillaris. It is also possible that they have additional functions, as suggested for similar processes in other tissues. They are not necessarily the harbinger of choroidal neovascularization, although growth of new vessels may result from distortion of this normal attribute.