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Etymology: L, orbiculus, little circle; cilium, eyelash
one of the two zones of the ciliary body of the eye, extending from the ora serrata of the retina to the ciliary processes at the margin of the iris. The orbicularis ciliaris is about 4 mm wide and increases in thickness as it approaches the ciliary processes.
Part of the uvea, anterior to the ora serrata and extending to the root of the iris where it is attached to the scleral spur. It comprises the ciliary muscle and the ciliary processes and is roughly triangular in sagittal section. The whole ciliary body forms a ring. The part just beyond the ora serrata is smooth and is thus known as pars plana (orbiculus ciliaris). Anterior to this lies a region of ridges, which are the ciliary processes; this region is called the pars plicata (corona ciliaris). From the sclera inward the ciliary body consists of: the supraciliaris (supraciliary layers) which is made up of strands of collagen containing melanocytes and fibroblasts; the ciliary stroma which contains blood vessels, melanocytes and the ciliary muscle; and the ciliary epithelium which comprises an inner non-pigmented layer and an outer pigmented layer and is a continuation of the internal limiting membrane of the retina and of the retinal pigment epithelium, respectively. The cells of these layers (particularly those of the non-pigmented layer) appear to be actively engaged in ion and water transport and the production of aqueous humour. See angle recession; cyclitis; iridodialysis; supraciliary space; stria; ultrafiltration.