Morphology of the developing choroidal vasculature in the human fetus.

In human fetuses with a gestation age of 12 to 22 weeks, the development of Haller's and Sattler's choroidal vascular layer was examined by both light and transmission electron microscopy. Even during week 12 arterioles could be identified. However, during this week they were only found in close association to the entrance of the optic nerve. Beginning with week 15/16, arterioles were also located outwards to the choriocapillary layer more anteriorly. When the arterioles first appeared, they exhibited the same ultrastructural features as those described in adults. Arteries first became apparent during week 22. They had not developed a complete internal elastic lamina. In contrast to those of the adult eye, smooth muscle cells of the fetal choroidal arteries exhibit glycogen granules. Haller's and Sattler's layer are both arterial and venous in nature.