Cataract

Alternative names:

lens opacity

Definition:

A cloudy area in the lens of the eye (See also congenital cataracts).

Causes, incidence, and risk factors:

The lens of an eye is normally clear. If the lens becomes cloudy or is opacified it is called a cataract. Cataracts may be present at or shortly after birth in which case they are called congenital cataracts. Adult cataract develops with advancing age, tends to run in families, and the appearance may be accelerated by environmental factors. Cataract may develop at any time throughout life following an eye injury in which the capsule of the lens is damaged. Cataract may also develop in response to metabolic diseases such as diabetes.

Congenital cataracts are cataracts which are present from birth (or appear shortly after). They may be familial (autosomal dominant inheritance), or they may be caused by congenital infections such as rubella, or associated with metabolic disorders such as galactosemia. Risk factors include inherited metabolic diseases, a family history of cataract, and maternal viral infection.

Adult cataract is generally associated with aging. It develops slowly and painlessly with a gradual loss of vision. Visual problems may be heralded by difficulty seeing at night, halos around lights or glare when looking at lights, and finally, decreased visual acuity, even in daylight.

Adult cataracts are classified as immature, mature, or hypermature. A lens that has some remaining clear areas is referred to as an immature cataract. A mature cataract is completely opaque; a hypermature cataract has a liquefied surface that leaks through the capsule and may cause inflammation.

Most people develop some clouding of the lens after the age of 60. About 50 percent of Americans ages 65 to 74 have cataract and about 70 percent of those age 75 and over have it. Most people with cataract have it in both eyes, although one eye may be worse than the other. Many people with cataract don't even know they have it.

Other factors that may contribute to cataract development are low serum calcium levels, diabetes, long-term use of corticosteroids, and other inflammatory and metabolic disorders. Other causes include trauma, radiation exposure, and excessive exposure to ultraviolet light (sunlight). In many cases, the cause of cataract is unknown.