Human fetal iridocorneal angle: a light and scanning electron microscopic study.

The iridocorneal angle and inner layers of the trabecular meshwork in human fetal eyes were studied by scanning electron microscopy. Tissue from 32 eyes of 17 fetuses with a gestational age from 12 to 22 weeks were investigated in order to determine the morphological changes in the cellular lining of the anterior chamber angle recess during development. The findings indicate that, although hexagonal corneal endothelial profiles extend almost to the angle apex in a few of the younger eyes examined (12-14 weeks), the lining is always perforated by a few discrete intercellular gaps (2-6 microns diameter). As development progresses it becomes clearer that the maturing meshwork is lined by uveal trabecular endothelial cells which are morphologically distinguishable from corneal endothelium. The frequency and size of the gaps between the inner uveal trabecular endothelial cells increase and are well developed by 18-20 weeks, clearly providing a route of communication between the fetal anterior chamber and the developing intercellular spaces in the primitive trabecular tissue. The implications of these observations on the 'Barkan's membrane' theory of congenital glaucoma are discussed.