[Prenatal development of human retinal vessels]

Feeding of the retina, whose thickness does not exceed 130 mu km, is possible at the account of chriocapillary diffusion. Should this threshold be topped (approximately by the 3.5th prenatal month), it will result in a relative hypoxia of the uttermost internal strata of the retina, which induces the appearance of new feeding source, i.e. retinal vessels. First, dense cellular steaks of the sequential fusiform cells originating from the visual-stem depth located near the wall of a. hyaloidea emerge in the surface retinal strata. These cells (angioblasts) formed the peripapillary plexus, shaped as a vascular pattern, and represented a non-lumenized prototype, or matrix, of a future capillary network. Later, main arterioles emerged, in the outward direction from them, and after that venules took shape from the above network through a partial reduction of vessels and a redistribution of blood circulation. The second deep capillary stratum was formed rather through a prolongation and "sagging" of the surface capillary loops than through gemmation; it is common for the entire retina and, unlike the surface stratum, is not divided by main arterioles into adjoining segments. By the 8th fetal-life month the evolution of the retinal bloodstream is not entirely completed, though it resembles, to a great extent, a definitive one.