Ultrastructure of the ciliary process vasculature in cynomolgus monkeys.

The ultrastructure of the ciliary process vasculature in cynomolgus monkeys is described with transmission electron microscopy. Special attention is paid to a special segment of the anterior arterioles (afferent segment) and to the end of the marginal venule (efferent segment)-vascular structures which have been described as haemodynamically important. The major arterial circle of iris (MACI), the exclusive blood supply of the ciliary processes, has only a one- or two-layered medium. A short distance after the anterior arterioles of the ciliary processes have branched off, these arterioles develop a characteristic segment of about 100 microns in length and which possesses a two-layered medium where prominent special myocytes lie on the adventitial side (afferent segment). Nerve endings with dense-core and large vesicles are closely associated to the vessel wall of these afferent segments. On the 'venous' side of the ciliary process vasculature, the very thin wall of the marginal ciliary process vessel becomes reinforced by a layer of myocytes in a segment which is located in the zone where the marginal vessel bends into the layer of the pars plana venules (efferent segment). Here, the endothelium is substantially thickened and filled with different-sized granules. Nerve endings with clear- and large dense-core vesicles lie around this segment.