Light enters the eye through the transparent cornea, located at the very front of the eye. It then passes through the pupil, the black center of the eye. This in fact is the aperture in the iris, which gives eyes their color. The iris can open and close, thereby causing the size of the pupil to change. By varying the size of the opening, the amount of light entering the eye can be controlled. If the light is very bright, the pupil is small and, when it is dark, the pupil is wide open.
After light passes through the pupil, it is focused by the lens, behind the iris. The focused light rays are directed to the retina, which is located at the back of the eye and contains special cells that translate the light images into nerve messages. These are carried by the optic nerves from the retina to the brain, where they are interpreted.
Illness can affect one or many parts of the eye. Some problems, such as infection, affect people at any age, whereas others are more likely to occur as you grow older. In the older person a decrease or loss of vision can be devastating because it interferes with feelings of self-worth and exaggerates the effects of isolation, dependency, and loneliness. If you are not able to read or watch television, you may become cut off from the everyday activities of the world. You should have a thorough periodic examination by a physician or ophthalmologist to ensure that your vision has not deteriorated as the result of disease. Any sudden change in vision should be checked immediately, because many illnesses that cause blindness can be prevented or treated.
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