Judy Landry, age 13, of Missoula, Mont., for her question:
WHAT CAUSES CATARACTS?
A cataract is a clouding of the lens of the eye. Cataracts occur for a variety of reasons with the most frequent cause, perhaps, resulting from aging. This type is called senile cataract and it can produce complete clouding or 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.
Many cataracts start 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 opaque, or nontransparent.
Medical experts don't know how to prevent or cure most kinds of cataracts, but sight can be restored to most cataract patients. 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 then be used to provide good focusing.
In some cases, eye surgeons implant or place an artificial plastic lens in the eye. 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 entirely as well at all distances.
The lens helps the eye focus. Light rays from the object first strike the cornea, the transparent part of the outside of the eyeball. The cornea then 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.
A contact lens is a plastic eyeglass that is worn directly on the eye. Most contact lenses are about the size of a person's little fingernail. They float on a thin layer of tears on the surface of the cornea.
Most persons who have had cataracts removed can see much better with contact lenses than they can see with ordinary glasses.