Optic nerve head microvasculature of the rabbit eye.

Vascular luminal castings of rabbit eyes were microdissected and studied with scanning electron microscopy to elucidate the three-dimensional angioarchitecture of the optic nerve head. Using sequential microdissection, an incomplete arterial circle was identified as terminal branches of two to three short posterior ciliary arteries around the optic nerve head. Several recurrent branches from the arterial circle form a pial arterial network. This pial system supplies the optic nerve head microvasculature and receives numerous venules from them. The only large vessel to enter the optic nerve is a central retinal artery that has few branches within the optic nerve and provides several branches at the surface of the optic disc. Moderately numerous vessels connect the retinal and ciliary vascular layers within the optic nerve head. Few arterioles to the optic nerve head arise from the choroid; however, there are a small number of capillary and numerous venous connections between them. These results indicate that the principal blood supply of the rabbit optic nerve head is derived from the short posterior ciliary arteries by the arterial circle. The retinal arteries contribute to the surface vasculature of the optic nerve head. The pial system also plays a significant role in both supply and drainage of the rabbit optic nerve head.