Corpus: Ciliary body

In veterinary medicine, the term corpus ciliare refers to the ring-shaped part of the middle eye skin (tunica vasculosa bulbi), which is responsible for the suspension of the lens and is involved in aqueous humour production. It can be compared with the ciliary body in humans.

The ray body consists of a vascularised and pigmented connective tissue mass that lies circularly around the lens. Towards the front, the ray body merges into the iris. In carnivores, the ciliary body is approximately circular, whereas in other domestic mammals it is narrower ventrally and thus appears asymmetrical. In this area, the light-sensitive retina extends further forwards, which leads to an enlargement of the caudolateral field of vision.

In the peripheral area of the ray body, also known as the ciliary ring (orbiculus ciliaris), there are meridionally orientated fine ciliary folds (plicae ciliares). The central area, on the other hand, has strong, radially arranged folds. These folds are called ciliary processes (processus ciliares), which together form the so-called ciliary cortex (corona ciliaris). A large number of zonular fibres (fibrae zonulares) extend from the processus ciliares, which attach to the lens equator and thus form the suspension apparatus of the lens.

A two-layer epithelial layer adjoins the stroma of the ray body on the posterior side, whereby the posterior layer is unpigmented and the anterior layer is pigmented. These epithelial layers are involved in aqueous humour formation.

A smooth muscle, the so-called ciliary muscle, is embedded in the ciliary body. The ciliary muscle is strongly developed in carnivores, but relatively weak in ungulates. The function of this parasympathetically innervated muscle is to accommodate the lens. Tensing this muscle leads to relaxation of the zonular fibres, which allows the lens to round off with the help of its own elasticity. This results in near accommodation. Conversely, the relaxation of this muscle causes the zonular fibres to tense and thus flattens the lens (far accommodation).

The ciliary body is also involved in the production of aqueous humour.

• Salomon FV, Geyer H, Uwe G. 2008. anatomy for veterinary medicine. 2nd, updated and expanded edition. Stuttgart: Enke Verlag in MVS Medizinverlage Stuttgart GmbH & Co. KG. ISBN: 978-3-8304-1075-1
• Nickel R, Schummer A, Seiferle E. 2003. Textbook of Anatomy of Domestic Animals, Volume IV: Nervous System. 4th, unchanged edition. Stuttgart: Parey in MSV Medizinverlage Stuttgart GmbH & Co. KG. ISBN: 978-3-8304-4150-2