Jessica LaChance, age 13, of Camden, N.J., for her question:
WHAT IS A CATARACT OF THE EYE?
A cataract is the clouding of the lens of the eye.
Many cataracts of the eye begin as small spots in the lens that interfere slightly with vision. They may cause blindness by spreading until the entire lens becomes milky white and opaquue or non transparent.
The lens helps the eye focus. Light rays from an object first strike the cornea, the transparent part of the outside of the eyeball. The cornea bends the light rays toward each other, but not enough to focus them into an image.
The light rays then pass through the lens, which bends them further and causes them to focus an image on the retina, or back layer of the eyeball. Because the lens is flexible, it can change shape to help a person focus on objects at different distances. Thus, clear vision depends on light passing through the cornea and lens easily and on the lens, focusing correctly.
Cataracts occur for a variety of reasons. Senile cataract results from aging. It occurs more frequently than any other form of the condition and eventually produces complete opaqueness of the lens.
Some cataracts result from such eye inflammations as iritis or from injuries to the eye. Diabetes can also cause cataracts.
Cataracts may develop if the parathyroid gland, which controls the amount of calcium in the body, does not work properly. Also, some babies are born with cataracts. Such cataracts may be caused by an infection before birth or by abnormal chemical processes in the body.
Doctors do not know how to prevent or cure most kinds of cataracts, but sight can be restored to most cataract patients. Often the lens must be removed by surgery. Light can then reach the retina, but it cannot be focused properly. Special glasses or contact lenses can provide good focusing.
In some cases, eye surgeons implant or place an artificial plastic lens in the eye to correct a cataract problem.
Most persons who have had cataract surgery can see well enough to carry on their normal activities. But glasses, contact lenses and implanted lenses are not flexible, as the natural lens was, and so the patient cannot see objects equally well at all distances.
In the normal eye, protein fibers in the lens are transparent. In the formation of cataracts, the protein becomes chemically changed, or denatured, and gradually coagulates in spots which become opaque.
Although eyestrain is not good for the eyes, lots of reading, close work such as sewing, and watching motion pictures or TV are not known causes of cataracts. Sitting too close to a defective color television set, however, may harm your eyes if radiation is emitted.
Advanced and untreated glaucoma an increase in fluid pressure within the forward part of the eye may result in cataracts, but otherwise there is no connection between the two disorders.