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

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.

Until a person is around age 45, the shape of the lens is able to change. This allows the lens to focus on an object, whether it is close or far away.

As we age, proteins in the lens begin to break down and the lens becomes cloudy. What the eye sees may appear blurry. This condition is known as a cataract.

Factors that may speed up cataract formation are:

• Diabetes
• Eye inflammation
• Eye injury
• Family history of cataracts
• Long-term use of corticosteroids (taken by mouth) or certain other medications
• Radiation exposure
• Smoking
• Surgery for another eye problem
• Too much exposure to ultraviolet light (sunlight)

In many cases, the cause of cataract is unknown.

Symptoms

Adult cataracts develop slowly and painlessly. Vision in the affected eye or eyes slowly gets worse.

• Mild clouding of the lens often occurs after age 60, but it may not cause any vision problems.
• By age 75, most people have cataracts that affect their vision.

Visual problems may include the following changes:

• Being sensitive to glare
• Cloudy, fuzzy, foggy, or filmy vision
• Difficulty seeing at night or in dim light
• Double vision
• Loss of color intensity
• Problems seeing shapes against a background or the difference between shades of colors
• Seeing halos around lights

Cataracts generally lead to decreased vision, even in daylight. Most people with cataracts have similar changes in both eyes, although one eye may be worse than the other. Many people with this condition have only mild vision changes.

Other symptoms may include:

• Frequent changes in eyeglass prescription

Signs and tests

A standard eye exam 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.

Treatment

The following may help people who have an early cataract:

• Better eyeglasses
• Better lighting
• Magnifying lenses
• Sunglasses

As vision gets worse, you may need to make changes around the home to avoid falls and injuries.

The only treatment for a cataract is surgery to remove it. Surgery is done if you cannot perform normal activities, such as driving, reading, or looking at computer or video screens, even with glasses.

If a cataract is not bothersome, surgery is usually not necessary. Cataracts usually do not harm your eye, so you can have surgery when it is convenient for you.

However, some people may have additional eye problems, such as diabetic retinopathy, that cannot be treated without first having cataract surgery.

For information on surgery, see: Cataract surgery

Expectations (prognosis)

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

Complications

Early diagnosis and treatment are key to preventing permanent vision problems.

Although rare, a cataract that goes on to an advanced stage (called a hypermature cataract) can begin to leak into other parts of the eye. This may cause a painful form of glaucoma and inflammation inside the eye.

Calling your health care provider

Call for an appointment with your health care provider if you have:

• Decreased night vision
• Problems with glare
• Vision loss

Prevention

The best prevention involves controlling diseases that increase the risk of a cataract, and avoiding exposure to factors known to promote cataract formation.

Wearing sunglasses when you are outside during the day can reduce the amount of ultraviolet (UV) light your eyes are exposed to. Some sunglasses do not filter out the harmful UV. An optician should be able to tell you which sunglasses filter out the most UV. For patients who smoke cigarettes, quitting will decrease the risk of cataracts.

References

1. Zigler JS Jr, Datiles MB III. Pathogenesis of cataracts. In: Tasman W, Jaeger EA, eds. Duane's Ophthalmology. 15th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2011:chap 72B.
2. Howes FW. Indications for lens surgery/indications for application of different lens surgery techniques. In: Yanoff M, Duker JS, eds. Ophthalmology. 3rd ed. St. Louis, Mo: Mosby Elsevier; 2008:chap 5.4.

Review Date: 9/16/2011.

Reviewed by: 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.