Anatomy of the Eye
A cross section of the human eye can be seen on the right. The structure of the eye allows it to function much like a camera. In a camera, a lens focuses light onto a lens. In a camera, a convex lens focuses an image onto fim or a digital sensor. See below.
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In the human eye, light enters through the cornea. The cornea is mainly composed of the protein collagen and protects they eye and does most of the refration that focuses the light. The iris is a circular ring of muscle that controls the size of the pupil, the hole througth which light travels into the eye. The iris is easily visible as the ring that surrounds the dark part of the eye. The pigmentation of the iris determines eye color. After light moves through the pupil, it strikes the lens. The lens is made of proteins called crystallins. The lens is convex in shaple and only contributes a small amount to the focusing of light. The main feature of the lens though is its ability to change shape. Muscles attached to the lens can change its shape. This changes how light is refracted as it passes through the lens effectively allowing the eye to be focused. The light passes throught the vitreous humor, a gel like sustance that helps to shape the eyeball, before striking the retina. The retina is a specialized layer of neural cells at the back of the eyeball. The lens and cornea focus light onto the retina. When light strikes retinal cells, it changes the chemical composition of cells in the retina. This information is then carried via the optic nerve to the brain. Where the information is processed and interpreted.