Retinal Vascular Patterns

Tryptic digestion of the retina with subsequent staining by suitable dyes has permitted identification of two types of cells associated with the capillary wall. One type is the endothelial cell lining the lumen. The other type we have elected to call the mural cell because it is encased within the vessel wall, covered on both its inner and outer surfaces by basement membrane. At the present writing we are unable to state whether or not mural cells comparable to those in the retinal capillaries exist elsewhere in the body; we have not found them in capillaries of connective tissue, conjunctiva, or choroid. Nevertheless they are regularly present in intraretinal capillaries of all mammals studied (man, monkey, cat, dog, beef, hamster, mouse, and rat) while being invariably absent from extraretinal capillaries such as those supplying the rabbit retina and the frog retina. They are also lacking in vessels that proliferate pathologically