What is the function of the ciliary body in the eye?

The ciliary body plays a crucial role in the eye's focus mechanism by controlling the shape of the lens. When the ciliary muscles contract, they release tension on the zonules (the fibers connecting the ciliary body to the lens), allowing the lens to become thicker and more convex. This adjustment enables the eye to focus on nearby objects. Conversely, when the ciliary muscles relax, the lens flattens, which is essential for viewing distant objects. This ability to alter the lens shape for focusing is known as accommodation, making the ciliary body integral to our visual clarity at various distances.

The other options do not relate to the primary function of the ciliary body; protecting the retina and receiving visual information are functions associated with other parts of the eye, and the drainage of tears is managed by the lacrimal system.