Regional microvascular anatomy of the rabbit ciliary body.

Vascular luminal castings of rabbit eyes were microdissected and studied with the scanning electron microscope to delineate the anatomy of the ciliary body microvasculature. We found regional microvascular differences corresponding to well known gross topographical and ultrastructural differences that may indicate regional functional specialization. The major arterial circle of the iris, derived solely from the long posterior ciliary arteries, supplies the ciliary body via two types of arterioles: anterior and posterior. Spiral iridial process capillaries arise from the anterior (iris) arterioles, are radially arranged along the back of the iris and drain directly into the iris veins. Arterioles from the posterior (ciliary) arterioles enter the head of the process, supplying its tortuous capillaries, some of which drain back into the iris veins. Other capillaries turn posteriorly to form relatively straight, parallel capillaries within the process leaf that drain into the choroidal system via marginal process veins. More posterior arterioles supply capillaries to the base of major processes, to the interprocess ciliary web, and to minor processes. The presence of a dual arteriolar supply to the ciliary processes has also been found in primates and suggests that the rabbit may represent a suitable animal model for the study of factors governing regional ciliary process perfusion.