Ultrastructure of the hyaloid vascular system

The hyaloid vascular system is an extensive, transitory network of intraocular blood vessels. The hyaloid artery runs from the optic disc to the posterior pole of the lens, giving off branches which fill the vitreous—the vasa hyaloidea propria. When the hyaloid artery reaches the lens, it divides into branches which ramify along the posterior lens capsule—the tunica vasculosa lentis. The electron microscope reveals that the capillaries of the vasa hyaloidea propria and tunica vasculosa lentis are of the A-1-alpha structure, with a continuous nonfenestrated endothelial lining, a continuous basement membrane, and an interrupted pericyte lining. The hyaloid artery has the fine structure of a typical arteriole, with a prominent tunica media of smooth muscle. After their function is complete, the hyaloid capillaries involute, become occluded by macrophages, and eventually disappear.