HYALOID VESSELS OF THE HUMAN FETAL EYE - A SCANNING ELECTRON-MICROSCOPIC STUDY OF CORROSION CASTS

Objective: Microscopic investigation of the hyaloid vascular system in 5-month-old human fetuses. Methods: Corrosion casting and light and s canning electron microscopy. Results: The hyaloid artery ramifies into a tuft of vasa hyaloidea propria, which communicates with the posteri or portion of the tunica vasculosa lentis, characterized by a network of anastomosing vessels. They further pass to the lateral portion of t he tunica, acquiring a nonanastomosing palisadelike array and drain in to the vessels of the ciliary processes or, after bending over the edg e of the developing iris, drain into the outer choriocapillaris. The t unica vasculosa lentis vessels also communicate with the pupillary mem brane, a system of vascular arcades arranged in several interconnected tiers, supplied by the terminal branches of the long posterior ciliar y arteries. In tunica vasculosa lentis, arterioles seem to pass direct ly into veins, without forming a capillary bed. Conclusions: At the in vestigated developmental stage, the fully developed hyaloid system ent ers its subsequent involution, and the vessels nourishing the vitreous have already involuted. The system is generally similar to that obser ved in other mammals.