The ciliary body is the circumferential tissue inside the eye composed of the ciliary muscle and ciliary processes. It is triangular in horizontal section and is coated by a double layer, the ciliary epithelium. This epithelium produces the aqueous humor. The inner layer is transparent and covers the vitreous body, and is continuous from the neural tissue of the retina. The outer layer is highly pigmented, continuous with the retinal pigment epithelium, and constitutes the cells of the dilator muscle. This double membrane is often regarded to be continuous with the retina and a rudiment of the embryological correspondent to the retina. The inner layer is unpigmented until it reaches the iris, where it takes on pigment. The retina ends at the ora serrata. It is part of the uveal tract— the layer of tissue which provides most of the nutrients in the eye. It extends from the ora serrata to the root of the iris. There are three sets of ciliary muscles in the eye, the longitudinal, radial, and circular muscles. They are near the front of the eye, above and below the lens. They are attached to the lens by connective tissue called the zonule of Zinn, and are responsible for shaping the lens to focus light on the retina. The ciliary body receives parasympathetic innervation from the oculomotor nerve.
The ciliary body has three functions: accommodation, aqueous humor production and the production and maintenance of the lens zonules. It also anchors the lens in place. Accommodation essentially means that when the ciliary muscle contracts, the lens becomes more convex, generally improving the focus for closer objects. When it relaxes it flattens the lens, generally improving the focus for farther objects. One of the essential roles of the ciliary body is also the production of the aqueous humor, which is responsible for providing most of the nutrients for the lens and the cornea and involved in waste management of these areas.
The ciliary body is the main target of drugs against glaucoma (apraclonidine) as it is responsible for aqueous humor production. Its inhibition leads to the lowering of aqueous humor production and causes a subsequent drop in the intraocular pressure.
- ^ Cassin, B. and Solomon, S. Dictionary of Eye Terminology. Gainsville, Florida: Triad Publishing Company, 1990.
- ^ Lang, G. Ophthalmology: A Pocket Textbook Atlas, 2 ed.. Pg. 207. Ulm, Germany. 2007.