Alternative Names

Lens opacity; Age-related cataract

Definition of Cataract

A cataract is a clouding of the lens of the eye.

Causes, incidence, and risk factors

The lens of the eye is normally clear. It acts like the lens on a camera, focusing light as it passes to the back of the eye.

Signs and tests

A and slit-lamp examination are used to diagnose cataracts. Other diagnostic tests are rarely needed, except to rule out other possible causes of poor vision.


The following may help people who have an early cataract:

Expectations (prognosis)

Vision may not improve to 20/20 after cataract surgery if other eye diseases, such as , are present. Ophthalmologists can usually, but not always, determine this in advance.


Franklin W. Lusby, MD, Ophthalmologist, Lusby Vision Institute, La Jolla, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. – 8/31/2010

Slit-lamp exam
Cataract - close-up of the eye
Cataract surgery  - series

ADAM Medical Encyclopedia

Article written by

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission ( URAC's accreditation program is an independent audit to verify that A.D.A.M. follows rigorous standards of quality and accountability.