The vitreus, an intraocular compartment of the leptomeninx. Electron microscopic observations on rat eyes.

In the 16-day rat embryo and in 2 and 15 days old postnatal rats the macrophage- and fibroblast-like cells of the vitreus are not different from those of the developing leptomeninx. There is also no difference in the ultrastructure of the developing blood vessels. Both vitreus and leptomeninx are separated from the neuroectodermal tissues by a basal lamina. Regarding the embryonic development, the entire intraocular cavity except the lens, is a special cleared-out portion of the former mesenchymal tissues surrounding the central nervous system including the eye cup (meninx primitiva). It may be interpreted as analogous to a leptomeningeal cisterna. The largest part of this intraocular cisterna is the vitreus. The pathogenesis of diseases occurring simultaneously in the leptomeninx, the uvea, and the vitreus, possibly may have some relation to the common embryologic origin of the affected tissues.