The eye is often compared to a camera. Each gathers light and then transforms that light into a picture. Both also have lenses to focus the incoming light. Just as a camera focuses light onto the film to create a picture, the eye focuses light onto a specialized layer of cells, called the retina, to produce an image.
Sight begins when light rays from an object enter the eye through the cornea, the clear front of the eyeball. The cornea is actually responsible for about sixty percent of the eyeball’s light-ray-bending capability. The cornea’s refractive power bends the light rays in such a way that they pass freely through the pupil, the size-changing hole in the iris.
The iris, the structure that gives the eyes color, works like a shutter in a camera. It could enlarge and shrink, depending on how much light the environment is sending into the pupil.
After passing through the iris, the light rays strike the eye’s crystalline lens. This clear, flexible structure works much like the lens in a camera – shortening and lengthening its width in order to focus light rays properly.
Light focused by the cornea and crystalline lens then reaches the retina, the light-sensitive inner lining of the back of the eye. The retina’s function is much like the film in a camera. It is responsible for capturing all of the light rays, processing them into light impulses through millions of tiny nerve endings, then sending these light impulses through over a million nerve fibers to the optic nerve.
The optic nerve acts like an extension of the brain. It is a bundled cord of more than a million nerve fibers. The light impulses travel through this nerve fiber to the brain, where they are interpreted as an image.