The ciliary body is a ring-like, anterior thickened portion of the vascular layer of the eyeball that is continuous with the iris (Read more!) anteriorly and the choroid (Read more!) posteriorly. It is located just anterior to the ora serrata (Read more!).

In cross-sectional studies, the ciliary body appears triangular, with its base directed toward the iris and its apex toward the choroid. Overall, the ciliary body is composed of several specialized structures, including the ciliary processes, ciliary muscle, and ciliary epithelium.

The anterior portion of the ciliary body, called the corona ciliaris or ciliary crown (also pars plicata), is thickened and folded and continuous with the posterior surface of the iris. In contrast, the posterior portion, known as the orbiculus ciliaris or ciliary ring (also pars plana), is thin, smooth, highly pigmented, and flat. It is continuous with the choroid at the ora serrata.

The inner surface of the corona ciliaris contains around 70-80 small, thin, finger-like projections known as the ciliary processes and an equal number of smaller ridges called the ciliary folds between them. The ciliary processes are radially oriented and attached to the lens (Read more!) via the zonular fibers (suspensory ligaments of the lens), participating in the accommodation reflex and helping maintain the position of the lens.

Additionally, the ciliary body is highly vascularized and covered by a specialized, double-layered ciliary epithelium. The outer layer, known as the pigmented layer, consists of cuboidal cells rich in melanin. The inner non-pigmented layer consists of columnar cells that produce aqueous humor in the posterior chamber of the eyeball. The folding of the ciliary processes increases the surface area of the epithelium, optimizing aqueous humor production.

The largest portion of the ciliary stroma is occupied by the smooth muscle cells that form the ciliary muscle. This muscle is composed of fiber groups arranged in three orientations - longitudinal or meridional fibers, circular fibers, and radial fibers. The longitudinal fibers are collectively called the Brücke's muscle, the circular fibers form the Müller's muscle, and the radial fibers are known as the Rouget's muscle.

Contractions of the ciliary muscle reduce tension in the zonular fibers, allowing the lens to become more convex. This increases its refractive power, enabling the eye to focus on near objects. This process is called accommodation, by which the eye adapts to view objects at different distances. When the ciliary muscle relaxes, the zonular fibers tighten, and the lens flattens. Therefore, the ciliary muscle plays a key role in accommodation.

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Ciliary body