How the Body Works: The Focusing Mechanism

The focusing mechanism of the eye consists of the lens, which is completely encircled by the ciliary muscles and attached to them by the suspensory ligaments. In distant vision the ciliary muscles are relaxed and the lens is pulled flat. It does little focusing because the almost parallel light rays from the distant object need to be only slightly refracted to bring them to a point on the retina. In near vision, the ciliary muscles contract, the suspensory ligaments loosen and the lens becomes more convex. The curved surface of the lens reinforces the cornea's focusing of the more divergent rays from the near object.