The developmental and aging processes of Schlemm's canals.

Schlemm's canal (Sinus venous sclerae) of human fetuses and postnatal monkeys (Macaca fuscata) were observed with the light and electron microscope. Between the 21st and 24th week of gestation of the fetuses, many branches of Schlemm's vascular plexus at the sclerocorneal junction, which is immatured form of Schlemm's canal, were connected to each other by young fibroblasts invading from the surrounding connective tissue. Our observations indicate that the main pathway of aqueous humor across endothelium of the canal is converted from "intercellular" into "intracellular" (transported by vacuoles and pores) in these stages. In the postnatal monkeys, large vacuoles were observed in the dif f erentiatin.g endothelium at the inner wall of the canal. Our electron micrographs indicate that these vacuoles are formed by a successive fusion of adjacent pinocytotic vesicles in the endothelial cells and take an important role for aqueous humor transport.