Ophthalmology => Cataract
Cataract (vision), in medicine, opaque condition of the lens of the eye or of its capsule. Its position behind the pupil readily distinguishes this condition from opacities of the cornea. Cataract may affect the lens alone (lenticular), or the front or back of the capsule of the lens (capsular), or both lens and capsule (capsulolenticular). Cataract is painless and unaccompanied by inflammation. It causes blindness by obstructing passage of light, but the patient can distinguish light from darkness.
Traumatic cataract results from a perforating wound of the capsule of the lens. The entire lens becomes opaque, and a portion usually remains so; but at times, unless inflammation of other portions follows, the cloudiness entirely disappears. Congenital cataract is due to an intrauterine infection, chromosomal disorder, or metabolic disease that causes imperfect development or inflammation. Juvenile cataract may be hereditary. The lens is soft and white in both congenital and juvenile cataracts. Both are treated by "needling," an operation in which a needlelike knife or a laser beam is used to cut and break up the lens. The injured lens tissue is then absorbed by the body. Juvenile and adult cataracts can also be caused by exposure to radiation and by drugs such as glucocorticoids.
Senile cataract, the most common form, usually occurs in people over 50 years of age and generally involves both eyes. It may also occur at a younger age in people with diabetes mellitus. Beginning in the form of dark streaks extending from the periphery toward the center of the lens, or as spots in any portion, it eventually makes the entire lens opaque. As the fluid of the lens is absorbed, the lens becomes easily separated from its capsule and is considered mature, or "ripe" for operation. Later, if not extracted, the lens undergoes degenerative changes, or liquefies, and the capsule becomes thickened and opaque, making the results of operation less satisfactory. The only method of relieving senile cataract is extraction of the lens. Sight can be restored in most instances by wearing special eyeglasses or contact lenses or by a surgeon implanting an artificial lens in the affected eye.