The Essential Feature of the Eye

Light passes through the pupil; the lens focuses an image on the retina at the back of the eye, and the retina performs the first calculations on the image before transmitting its signals to the brain. For people with normal vision looking at distant objects, the lens gives a sharp focus when it is in its flattest state. To see objects that are only a few feet or less away, the lens must become rounder to give a sharp focus. To do this, the ciliary muscle, a circular muscle that surrounds the lens, contracts. As we age, our lenses become less elastic, so we need glasses to bring close objects into focus.