Ultrastructure of the human posterior tunica vasculosa lentis during early gestation.

In human embryos with a gestational age of from 7.6 to 14.0/15.0 weeks, the posterior tunica vasculosa lentis (TVL) was examined by both scanning and transmission electron microscopy. Even at the very early age of 7.6 weeks the tunica was found to be fully developed. It consisted of a radiating network of tortuous capillaries. Their walls were composed of a continuous layer of endothelial cells, surrounded by a basement membrane and a discontinuous sheath of pericytes. The thickness of the basement membrane increased with increasing gestational age. As opposed to previous studies, the endothelial cells exhibited transitory fenestrations. In the neighborhood of the posterior TVL macrophages were found.