Ciliary process microvasculature of the primate eye.

Using methylmethacrylate microvascular luminal castings, we studied the three-dimensional angioarchitecture of the primate ciliary process with the scanning electron microscope. We found that the ciliary processes are served by vessels that radiate anteriorly and posteriorly from the "major arterial circle" of the iris. The anterior arterioles possess focal constrictions and supply the anterior and marginal aspects of the major ciliary processes as well as interprocess networks that connect contiguous processes. The posterior arterioles lack focal constrictions and supply the minor ciliary processes via posterior interprocess networks. Major and minor ciliary process capillaries are irregularly dilated and pass posteriorly to drain into the choroidal veins. Finally, venous arcades exist which directly connect anterior and posterior interprocess networks with the choroidal veins and thus bypass the ciliary processes entirely. The presence of focal constrictions in the anterior arterioles suggests a site for possible autonomic or neurohumoral control of blood flow into the major ciliary processes.