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What Is a Cataract?

A cataract is a dense, cloudy area that forms in the lens of the eye. It develops at a slow rate and eventually interferes with your vision. You might end up with cataracts in both eyes, but they usually don’t form at the same time. Cataracts are common in older people. Over half of people in the United States have cataracts or have undergone cataract surgery by the time they’re 80 years old, according to the National Eye Institute.

Types of Cataracts

Age-related cataracts are divided into three types, depending on their location. Nuclear cataracts form in the middle of the lens and cause the nucleus, in the center, to become yellow or brown. Cortical cataracts are wedge-shaped and form around the edges of the nucleus. Posterior capsular cataracts form faster than the other two types and affect the back of the lens.

Congenital cataracts, which are present at birth or form during a baby’s first year, are less common than age-related cataracts. They occur in roughly one in every 10,000 infants, according to the University of Maryland Medical Center. This type of cataract does not always have symptoms and can be removed if it interferes with the baby’s vision. These cataracts can develop if the mother has an infection or uses drugs or alcohol while pregnant.

Secondary cataracts are caused by disease or medications. Diseases that are linked with the development of cataracts include glaucoma and diabetes. The use of the steroid prednisone and other medications can sometimes lead to cataracts.

Traumatic cataracts develop after an injury to the eye, although it can take several years for this to happen.

Radiation cataracts can form after a patient undergoes radiation treatment for cancer.

What Causes Cataracts?

Cataracts begin when proteins in the eye form clumps that prevent the lens from sending clear images to the retina. There are several underlying causes:

  • overproduction of oxygen-free radicals, or oxidants (an oxygen free radical is an oxygen molecule that has been chemically altered due to normal daily life)
  • smoking
  • ultraviolet radiation
  • long-term use of steroids and other medications
  • certain diseases, such as diabetes
  • trauma
  • radiation therapy

Risk Factors of Cataracts

Risk factors associated with cataracts include:

  • aging
  • heavy drinking
  • smoking
  • obesity
  • high blood pressure
  • previous eye injuries
  • family history
  • too much sun exposure

People with diabetes and those who have been exposed to radiation from X-rays and cancer treatments are also at higher risk.

Symptoms of Cataracts

Common symptoms of cataracts include:

  • blurry vision
  • trouble seeing at night
  • seeing colors as faded
  • increased sensitivity to glare
  • halos surrounding lights
  • double vision in the affected eye
  • frequent changes in glasses prescription

Diagnosing Cataracts

Your doctor will perform a comprehensive eye exam to check for cataracts. This will include an eye chart test to check your vision at different distances and tonometry to measure your eye pressure. The most common tonometry test uses a painless puff of air to flatten your cornea and test your eye pressure. Your doctor will also put drops in your eyes to make your pupils bigger. This makes it easier to check the optic nerve and retina for damage with a magnifying lens. Other tests your doctor might perform include checking your sensitivity to glare and your perception of colors.

Treatment of Cataracts

Non-surgical treatments for cataracts include stronger eyeglasses, magnifying lenses, and sunglasses with an anti-glare coating. Surgery is necessary when cataracts prevent you from going about your daily activities, such as reading or driving. It is also performed when cataracts interfere with the treatment of other eye problems. More than two million cataract surgeries are done in the United States annually, according to the University of Michigan Kellogg Eye Center. One surgical method, known as phacoemulsification, involves the use of ultrasound waves to break the lens apart and remove the pieces. Extracapsular surgery involves removing the cloudy part of the lens through a long incision in the cornea. After surgery, an artificial intraocular lens is placed where the natural lens was.


Cataracts can interfere with daily activities and lead to blindness when left untreated. Although some stop growing, they do not get smaller on their own. The surgical removal of cataracts is a very common procedure and is highly effective roughly 90 percent of the time, according to the National Eye Institute.

Prevention of Cataracts

To reduce your risk of developing cataracts:

  • protect your eyes from UVB rays by wearing sunglasses outside
  • have regular eye exams
  • stop smoking
  • eat fruits and vegetables that contain antioxidants
  • maintain a healthy weight
  • keep diabetes and other medical conditions in check.

Content licensed from:

Written by: Amanda Delgado and Jennifer Nelson
Published on: Aug 16, 2012
Medically reviewed : George Krucik, MD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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