The eyes enable man to see. The Retina, or light receiving part of the eye, contains thousands of special cells called rods or cones. These cells respond to light of certain wave lengths by sending messages through the optic nerve to the brain, to give impressions of light, form, and color. The Cornea, or clear front part of the eye, and the lens, behind the cornea, are transparent. They help focus the image of an object on the retina, much as the lens of a camera focuses light on film.

The iris, or colored part of the eye, lies behind the cornea and in front of the outer edge of the lens. It controls the amount of light entering the eye. Delicate muscles in the iris respond to changes in the intensity of light. They alter the size of the pupil, or colored part of the eye. The pupil is actually an opening in the iris. Light on it’s way to the retina passes through the pupil, the lens, and a fluid filled space in front of and behind the lens. The pupil becomes larger in dim light and smaller in bright light. In this way, it protects the sensitive cells of the retina.