This is a ring of muscle that sits behind the iris (the colored part of the eye). The ciliary body has two main functions – to focus the vision and to produce aqueous fluid. To help the eye focus, the ciliary muscle can contract like a sphincter. The ciliary body is attached to the lens by zonules (strings) in a 360-degree ring (like the springs on a trampoline). When the ciliary muscle contracts, the tension on the zonular springs relaxes and the lens changes shape accordingly. This helps focus the eye to see near objects. The ciliary body also has cells that produce the aqueous fluid that fills the front chambers of the eye. The production (and drainage) of this aqueous fluid is what determines the internal ocular pressure of the eye, which is important in our discussion of glaucoma.