The tunica vasculosa lentis; an expedient system for studying vascular formation and regression.

We examined, with scanning electron microscopy, the tunica vasculosa lentis of the postnatal rat. It consisted of an extensive two-dimensional capillary network, spreading over the posterior and lateral surfaces of the lens. During the postnatal days, capillaries were associated with incipient pericytes and frequently had sprouts with a lamellipodial extension. Stellate angioblastic cells occurred in the meshes of the vasculature, which attached to the pre-existing capillaries with their processes. Both capillary sprouts and angioblastic cells may be involved in vasculogenesis. At the eighteenth postnatal day, the tunica underwent remarkable regressive changes: many capillaries degenerated or were totally eliminated, leaving faint traces on the lens surface. What appeared to be macrophages adhered to degenerating capillaries. With its rapid developmental sequence reported previously and the findings obtained herein, the vasculature provides an expedient system to study the cytological mechanism involved in vascular formation and regression.