How we see
There are many different parts of the eye that help to create vision. Light passes through the cornea, the clear, dome-shaped surface that covers the front of the eye. The cornea bends - or refracts - this incoming light. The iris, the colored part of the eye, regulates the size of the pupil, the opening that controls the amount of light that enters the eye. Behind the pupil is the lens, a clear part of the eye that further focuses light, or an image, onto the retina. The retina is a thin, delicate, photosensitive tissue that contains the special "photoreceptor" cells that convert light into electrical signals. These electrical signals are processed further, and then travel from the retina of the eye to the brain through the optic nerve, a bundle of about one million nerve fibers. We "see" with our brains; our eyes collect visual information and begin this complex process.