The ciliary body is a circular structure that is an extension of the iris, the colored part of the eye. The ciliary body produces the fluid in the eye called aqueous humor. It also contains the ciliary muscle, which changes the shape of the lens when your eyes focus on a near object. This process is called accommodation.
Evans M. Anatomy of the uvea. In: Yanoff M, Duker JS, eds. Ophthalmology. 4th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 7.1.