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

The crystalline lens (often called simply the lens) is located directly behind the pupil and iris.  The lens helps the cornea focus light on the retina to begin the process of sight.  A cataract decreases the clarity of the lens and causes blurred vision. 

The word cataract comes from an ancient Greek term meaning "waterfall."  People with cataracts often feel as though they are trying to see the world through an opaque watery film or waterfall.

What causes cataracts?

The specific cause of cataracts is unknown, but the most common type of cataract develops in response to aging.

The crystalline lens consists mainly of water and protein.  The protein is arranged in a specific way to keep the lens clear and to allow light to pass through it.  As we age, the arrangement of the lens protein may become disrupted, causing the lens to become cloudy.  As cataracts worsen, vision becomes blurred and distorted.

Risk factors for cataracts (in addition to advancing age) include:

• Gender - Cataracts appear to be more common in women than men

• Race - Cataracts are more common in blacks than whites

• A family history of cataracts

• Long-term exposure to UV rays from sunlight

• Smoking

• Long-term use of steroid medications

• Diabetes

Types of cataracts

Though age-related cataracts are by far the most common, there are other types of cataracts as well, based on time of onset and cause:

• Congenital cataracts - These cataracts are present at birth or shortly thereafter.  May be related to premature birth or low birth weight.

• Secondary cataracts - These cataracts develop because of diabetes or other health problems.  Secondary cataracts are also sometimes linked to steroid use or radiation therapy.

• Traumatic cataracts - These cataracts develop after a serious eye injury - soon afterward or years later. 

How common are cataracts?

Because most cataracts are age-related, everyone is potentially at risk. 

About 50 percent of Americans ages 65 to 74 have some clouding of the crystalline lens.  This increases to 70 percent for those age 75 or older.

What are the symptoms of cataracts?

Symptoms of cataracts include:

• Blurred or hazy vision of gradual onset

• Increased glare, especially at night

• Sensitivity to light

• Colors appearing faded

• Frequent eyeglass prescription changes

• Double vision (or "ghost images") in one eye

What is the treatment for cataracts?

The only treatment for cataracts is surgery.  In cataract surgery, the cloudy crystalline lens is removed and replaced with a clear plastic lens. 

Cataract surgery is very successful at restoring vision.  Most people who have the procedure regain 20/20 vision.  And new lens implants can help you regain some of your near focusing as well.

Cataract surgery is one of the safest and most common surgical procedures performed in the United States.  Over 1.5 million cataract surgeries are done each year.

Can cataracts return after surgery?

Cataracts cannot return.  However, when the cloudy lens is removed in cataract surgery, the clear posterior capsule of the lens is usually left intact to keep the vitreous (the clear gel that fills the posterior cavity of the eye behind the lens) from leaking from the eye during surgery.

Months or years later, this thin capsule may become cloudy and caused blurred vision.  This is sometimes called an after-cataract.

An after-cataract can be treated with a short and painless laser procedure called a posterior capsulotomy.  In this procedure, a YAG laser removes the central cloudy portion of the lens capsule to restore clear vision.  Because the artificial lens remains firmly intact and is unaffected by the laser, there is little risk of vitreous leakage after a posterior capsulotomy.

Can cataracts be prevented?

There is some evidence that antioxidants and other nutritional supplements may slow or prevent the development of cataracts in some people.  However, additional study is needed to confirm this.  In the meantime, taking daily supplements that include riboflavin, vitamins C and E, carotenoids, zinc, and copper may be beneficial.

Because certain cataracts appear to be associated with exposure to ultraviolet (UV) radiation, it's wise to wear sunglasses outdoors that provide 100 percent UV protection.  A wide-brimmed hat also helps limit the amount of UV radiation reaching your eyes.