It is important for you to understand the parts of your eye involved with sight. These structures include the cornea, iris, pupil, lens, and retina.
Your cornea is a thin, clear layer on the outside of your eye. The iris, or the colored part of your eye, is a muscle that controls the amount of light going through your pupil. Behind the iris, sits the lens.
When light enters your eye, each light ray is bent twice. First, when it passes through the cornea, and again when it goes through the lens. The cornea and lens form the light rays into a beam of light that is focused directly onto your retina, where images are created. This image is then sent from the retina, through your optic nerve, to your brain for further processing.