A cataract is a clouding of the eye's lens that leads to decreased vision. The lens of the eye focuses an image onto the retina at the back of the eye. This is where an image is processed and then sent to the brain.

As the cataract matures, it often causes glare, as well as decreased vision, contrast and color sensitivity.


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The lens of the eye is made of mostly water and protein. The protein is arranged in a way that keeps the lens clear and lets light pass through it. A cataract forms when some of the protein clumps together and starts to cloud an area of the lens. A cataract won't spread from one eye to the other, although most people develop cataracts in both eyes at a similar times.

There are several causes of cataracts, including:

  • Aging (the most common cause)
  • Smoking
  • Diabetes
  • Infection
  • Injury
  • Exposure to radiation
  • Taking adrenal cortical hormones for a long time
  • Excessive exposure to sunlight
  • Birth defect

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

Risk factors include:

  • Age
  • Exposure to UV-B radiation from sunlight
  • Family members with cataracts
  • Diabetes
  • Trauma
  • Smoking


When a cataract is in the early stages, you may not notice any changes in your vision. Cataracts tend to mature slowly. Vision gets worse gradually. Some people with a cataract find that their close-up vision suddenly improves, but this is temporary. Vision is likely to worsen as the cataract becomes more cloudy. Because the decrease in vision is gradual, many people do not realize that they have cataracts until discovered during an otherwise routine eye examination.

Symptoms include:

  • Cloudy or blurry vision
  • Problems with light, including:
    • Headlights that seem too bright at night
    • Glare from lamps or very bright sunlight
    • A halo around lights
  • Colors seem faded
  • Poor night vision
  • Frequent changes in your eyeglass or contact lens prescription

These symptoms can also be a sign of other eye problems. If you have any of these symptoms, check with your eye care professional immediately.


Although you might think you have a cataract, the only way to know for sure is by having an eye examination. To detect a cataract, an eye specialist examines the lens and may do other tests to learn more about the structure and health of your eye.

A comprehensive eye examination usually includes:

  • Visual acuity test—an eye chart test that measures how well you see at various distances
  • Pupil dilation—the pupil is widened with eyedrops to see more of the lens and retina
  • Tonometry—a standard test to measure the pressure inside the eye; increased pressure may be a sign of glaucoma


For an early cataract, vision may be improved by using different eyeglasses, magnifying lenses, or stronger lighting. If these measures don't help or if vision loss interferes with your everyday activities, such as driving, reading, or watching TV, surgery is the only effective treatment.

Cataract surgery is almost never an emergency. Therefore, in most cases, waiting until you are ready to have cataract surgery will not harm your eye. However, your cataract will only get more cloudy with time.

Cataract surgery is almost always performed in one eye at a time. After the cloudy lens is removed, the eye surgeon (ophthalmologist) places an intraocular lens (IOL) in its place. An IOL is a clear lens that requires no care and becomes a permanent part of your eye.

After cataract surgery, most people need reading glasses and many people need glasses for distance. There is a relatively new option, multifocal intraocular lenses, which focus for both near and far distance in the same lens. Many patients who receive multifocal intraocular lenses see well at both a distance and nearby without glasses.

Although every surgery has risks, the majority of patients who have cataract surgery have better vision afterward.


Although there is no way to completely prevent cataracts, not smoking, consuming antioxidants (such as antioxidant vitamin supplements), and wearing a hat and UV-protected sunglasses when outdoors, may help. It is also important to get a comprehensive eye examination regularly. But since vision problems increase with age, if you are over age 60, you should have a comprehensive eye examination once a year.


American Academy of Ophthalmology

National Eye Institute, NIH


Canadian Family Physician

Canadian Ophthalmological Society


National Institutes of Health. Ophthalmic Genetics Newsletter . 2000 Summer;1(2).

National Institutes of Health website. Available at: .

Last reviewed March 2008 by Alexander J. Anetakis, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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