The ciliary muscle is a ring-shaped muscle located in the eye, specifically around the lens. Its primary function is to control the shape of the lens, allowing the eye to focus on objects at various distances. When the ciliary muscle contracts, the lens becomes thicker, enabling better focus on nearby objects. Conversely, when it relaxes, the lens flattens for distant vision. This muscle is part of the ciliary body, which also produces the aqueous humor, a fluid that nourishes the eye. The ciliary muscle works in conjunction with the iris, which controls the size of the pupil, further aiding in vision clarity.