A cataract is a painless, cloudy area in the lens of the eye. A cataract blocks light from reaching the retina (the nerve layer at the back of the eye) and may cause vision problems.

Cataracts are common in older adults and are associated with aging. Smoking and exposure to excessive sunlight are additional risk factors. Cataracts can also occur after an eye injury, as a complication of eye disease, after the use of certain medications, or because of certain medical conditions, such as diabetes. Some babies are born with cataracts or develop them shortly after birth. These are called congenital cataracts.

Cataracts in adults are treated with surgery if vision problems are interfering with the person's quality of life. Surgery to remove congenital cataracts is usually done during the first 3 months of a child's life.