The ciliary body is a ring-shaped structure approximately 6–7 mm wide that extends from the base of the iris and becomes continuous with the choroid at the ora serrata. The ciliary body is subdivided into 2 parts: the anterior pars plicata, which includes the ciliary processes, and the more posterior pars plana. The zonular fibers of the lens attach to the ciliary body in the valleys of the ciliary processes and along the pars plana. The inner portion of the ciliary body is lined by a double layer of epithelial cells: the inner, nonpigmented layer and the outer, pigmented layer (Fig 12-3).
Composed of smooth muscle fibers, the ciliary muscle comprises 3 layers of fibers: the outermost longitudinal layer, the middle radial layer, and the innermost circular layer. These individual muscle layers function as a unit during accommodation. Histologically, the layers are difficult to distinguish, and the muscle appears wedge-shaped in cross section.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.