A cataract is a clouding of the eye's lens. It 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, decreased vision, and contrast. Color sensitivity may also be lost if the cataract begins to turn yellow.

Copyright © Nucleus Medical Media, Inc.


The lens of the eye is made of mostly water and protein. The protein is arranged in a way that keeps the lens clear so light can 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 similar times.

There are several causes of cataracts, including:

  • Aging, the most common cause
  • Smoking
  • Diabetes
  • Certain infections
  • Exposure to radiation, certain toxins, or medications
  • Taking adrenal cortical hormones for a long time
  • Birth defect, inborn error of metabolism, or chromosomal abnormality

Risk Factors

Cataracts are common in older adults. Other factors that may increase your chance of a cataract include:

  • Excessive exposure to ultraviolet B (UV-B) radiation from sunlight
  • Family members with cataracts
  • Diabetes
  • Hypoparathyroidism
  • Eye trauma
  • Chronic eye disease, such as uveitis or retinitis pigmentosa
  • Smoking
  • Excessive alcohol
  • Autoimmune disorders, such as rheumatoid arthritis



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. This is only temporary. Vision is likely to get worse as the cataract becomes cloudier. Because the decrease in vision is gradual, many people do not realize that they have a cataract until it is discovered during a routine eye examination.

A cataract may cause:

  • Cloudy or blurry vision
  • Colors seem faded or images appear with a yellow tint
  • Poor contrast
  • Poor night vision
  • Difficulty reading
  • Double or multiple vision—this symptom often goes away as the cataract matures
  • Increased nearsightedness, requiring frequent changes in your eyeglass or contact lens prescription
  • Problems with light, including
    • Headlights that seem too bright at night
    • Glare from lamps or very bright sunlight
    • A halo around lights
    • Trying to read in bright light
    • Problems when moving from a dark area to a bright area
    • Colors seem faded
    • Poor night vision

These symptoms can also be signs of other eye problems. If you have any of these symptoms, check with your eye care professional right away.


The only way to diagnose a cataract is to have an eye examination. Your eye doctor will examine the lens or do some tests to learn more about the structure and health of your eye.

A comprehensive eye examination for cataracts usually includes:

  • Visual acuity assessment test (VAT)—To assess distant vision
  • Slit lamp exam—To magnify the eye
  • Tonometry—To assess fluid pressure inside the eye. Increased pressure may be a sign of glaucoma
  • Dilated eye exam—To evaluate the lens and the structures of the back of the eye



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 daily activities such as driving, reading, or watching TV, surgery is the only effective treatment.

Cataract surgery involves waiting until you are ready to have to have it so that it doesn't harm your eye. While you wait, your cataract will get cloudier with time.

Cataract surgery is almost always performed in one eye at a time. After the cloudy lens is removed, the eye surgeon 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 or for distance vision. There is a relatively new option, multifocal intraocular lenses, which focus for both near and far distances in the same lens. Many who receive multifocal intraocular lenses may not need to wear glasses.


To help reduce your chance of a cataract:

  • If you smoke, talk to your doctor about how to successfully quit.
  • Limit your alcohol intake.
  • Keep chronic conditions under control by following your treatment plan.
  • Wear a hat and UV-protected sunglasses when outdoors.
  • Talk to your doctor about vitamins or supplements.
  • Get regular eye exams.

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

Edits to original content made by Denver Health.


Eye Smart—American Ophthalmology 

National Eye Institute 


Canadian National Institute for the Blind 

Canadian Ophthalmological Society 


Cataracts in adults. EBSCO DynaMed Plus website. Available at:  . Updated October 23, 2017. Accessed September December 14, 2017.

Cataracts. National Eye Institute website. Available at: Updated September 2015. Accessed December 14, 2017.