A cataract is a cloudy area in the lens of the eye.

This article focuses on cataracts in adults. For information on cataracts in children, see: Congenital cataracts

The lens of the eye is normally clear. If the lens becomes cloudy, the condition is known as a cataract. Rarely, cataracts may be present at or shortly after birth. These are called congenital cataracts.

Adult cataracts usually develop very gradually with advancing age and may run in families. They develop slowly and painlessly, and vision in the affected eye or eyes slowly gets worse.

Cataracts develop more quickly if there are some environmental factors, such as smoking, exposure to other toxic substances, and exposure to excessive ultraviolet light or sunlight. They may develop at any time after an eye injury. Diseases such as diabetes also greatly increase the risk for cataracts. Certain medications, such as cortisone, can also speed up cataract formation.

Adult cataracts are classified as immature, mature, and hypermature.

• Immature cataract -- lens has some remaining clear areas
• Mature cataract -- completely cloudy, or opaque lens, which means you can't see through it
• Hypermature cataract -- lens tissues are breaking down and leaking through the surface covering, which can damage other structures in the eye

Most people develop some mild clouding of the lens after age 60. About 50% of people ages 65-74, and about 70% of those 75 and older have cataracts that affect their vision.

Factors that may contribute to cataract development are:

• Diseases that cause inflammation or affect metabolism
• Eye injury
• Family history
• Long-term use of corticosteroids or certain other medications
• Radiation exposure
• Smoking
• Too much exposure to ultraviolet light (sunlight)

In many cases, the cause of cataract is unknown.