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A cataract usually develops slowly and causes no pain. At first, the cloudiness may affect only a small part of the lens (a clear, elliptical structure near the front of each eye) and you may be unaware of any vision loss. Over time, however, as the cataract grows larger, it clouds more of your lens and distorts the light passing through the lens. Eventually, this impairs your vision because of overall blur or image distortion.

Signs and symptoms of cataracts include:

• Clouded, blurred or dim vision
• Increasing difficulty with vision at night
• Sensitivity to light and glare
• Halos around lights
• The need for brighter light for reading and other activities
• Frequent changes in eyeglass or contact lens prescription
• Fading or yellowing of colors
• Double vision in a single eye

If you have a cataract, light from the sun, lamps or oncoming headlights may seem too bright. Glare and halos around lights can make driving uncomfortable and dangerous. You may experience eyestrain or find yourself blinking more often to clear your vision.

Cataracts don't typically cause any change in the appearance of your eye. Pain, redness, itching, irritation, aching in your eye or a discharge from your eye aren't signs or symptoms of a cataract, but may be signs and symptoms of other eye disorders.

A cataract isn't dangerous to the physical health of your eye unless the cataract becomes completely white, a condition known as an overripe (hypermature) cataract. This can cause inflammation, pain and headache. A hypermature cataract requires removal if it's associated with inflammation or pain.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

A cataract can develop in one or both of your eyes. However, in most cases — except for those caused by injury or trauma — cataracts tend to develop symmetrically in both eyes. A cataract may or may not affect the entire lens.

When your eyes work properly, light passes through the cornea (the protective dome of clear tissue over the front of your eye) and the pupil (the hole in the center of your eye) to the lens. The lens is located just behind the iris (the colored part of your eye) and the pupil. It's shaped thicker in the middle and thinner near the edges. Tiny ligaments, which are bands of tough tissue fiber, hold it in place. The lens focuses light that passes through the cornea and pupil, producing clear, sharp images on the retina — the light-sensitive membrane on the back inside wall of your eyeball that functions like the film of a camera. As a cataract develops, the lens becomes clouded, which scatters the light and prevents a sharply defined image from reaching your retina. As a result, your vision becomes blurred.

The lens: Its makeup and its changes
The lens consists of three layers. The outer layer (capsule) is a thin, clear membrane. It surrounds a soft, clear material (cortex). The harder center of the lens is the nucleus. If you think of the lens as a piece of fruit, the capsule is the skin, the cortex is the fleshy fruit and the nucleus is the pit.

As you age, the lenses in your eyes become less flexible, less transparent and thicker. The lens is made mostly of water and protein fibers. The protein fibers are arranged in a precise manner that makes the lens clear and allows light to pass through without interference. With aging, the composition of the lens undergoes changes and the structure of the protein fibers breaks down. Some of the fibers begin to clump together, clouding small areas of the lens. As the cataract continues to develop, the clouding becomes denser and involves a greater part of the lens.

A cataract can form in any part of the lens.

Types of cataracts
Cataracts occur in three types:

• Nuclear. A nuclear cataract occurs in the center of the lens. In its early stages, as the lens changes the way it focuses light, you may become more nearsighted or even experience a temporary improvement in your reading vision. Some people actually stop needing their glasses. Unfortunately, this so-called second sight disappears as the lens gradually turns more densely yellow and further clouds your vision. As the cataract progresses, the lens may even turn brown. Seeing in dim light and driving at night may be especially troublesome. Advanced discoloration can lead to difficulty distinguishing between shades of blue and purple.
• Cortical. A cortical cataract begins as whitish, wedge-shaped opacities or streaks on the outer edge of the lens cortex. As it slowly progresses, the streaks extend to the center and interfere with light passing through the center of the lens. Problems with glare are common for people with this type of cataract.
• Subcapsular. A subcapsular cataract starts as a small, opaque area just under the capsule of the lens. It usually forms near the back of the lens, right in the path of light on its way to the retina. A subcapsular cataract often interferes with your reading vision, reduces your vision in bright light and causes glare or halos around lights at night.

Scientists don't know exactly why a lens changes with age. One possibility is damage caused by unstable molecules known as free radicals. Smoking and exposure to ultraviolet (UV) light are two sources of free radicals. General wear and tear on the lens over the years also may cause the changes in protein fibers.

Other causes of cataracts
Age-related changes in the lens aren't the only cause of cataracts. Some people are born with cataracts or develop them during childhood. Such cataracts may be the result of the mother having contracted German measles (rubella) during pregnancy. They may also be due to metabolic disorders. Congenital cataracts, as they're called, don't always affect vision, but if they do they're usually removed soon after detection.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

Everyone is at risk of developing cataracts simply because age is the greatest risk factor. By age 65 about half of all Americans have developed some degree of lens clouding, although it may not impair vision. After age 75, as many as 70 percent of Americans have cataracts that are significant enough to impair their vision.

Factors that increase your risk of cataracts include:

• Age
• Diabetes
• Family history of cataracts
• Previous eye injury or inflammation
• Previous eye surgery
• Prolonged use of corticosteroids
• Excessive exposure to sunlight
• Exposure to ionizing radiation
• Smoking

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

An eye specialist can detect and track the development of cataracts during routine eye exams. Have your eyes examined:

• Every two to four years until age 65 and every one to two years at age 65 and older
• Anytime you develop new eye problems

If you experience any signs and symptoms of cataracts, see your eye doctor. An eye doctor can diagnose cataracts with the help of a careful eye exam.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

The only way to know for sure if you have a cataract is to have an eye examination that includes several tests:

• Visual acuity test. Acuity refers to the sharpness of your vision or how clearly you see an object. In this test, your eye doctor checks to see how well you read letters from across the room. Your eyes are tested one at a time, while the other eye is covered. Using a chart with progressively smaller letters from top to bottom, your eye doctor determines if you have 20/20 vision or less acute vision.
• Slit-lamp examination. A slit lamp allows your eye doctor to see the structures at the front of your eye under magnification. The microscope is called a slit lamp because it uses an intense line of light — a slit — to illuminate your cornea, iris, lens and the space between your iris and cornea. The slit allows your doctor to view these structures in small sections, which makes it easier to detect any small abnormalities.

• Retinal examination. In this procedure, your eye doctor puts dilating drops in your eyes to open your pupils wide and provide a bigger window to the back of your eyes. Using a slit lamp or a special device called an ophthalmoscope, he or she can examine your lens for signs of a cataract and, if needed, determine how dense the clouding is. Your eye doctor will also check for glaucoma and, if you have blurred vision or discomfort, check for other problems involving the retina and the optic nerve.

  Dilating drops usually keep your pupils open for a few hours before their effect gradually wears off. Until then, you'll probably have difficulty focusing on close objects, while your distance vision is generally less affected. With your pupils open this wide, you may want sunglasses for your trip home, especially if it's a bright day. Also, it may be safer to let someone else do the driving.

If you have a cataract, you can discuss treatment options with your eye doctor. If — in addition to having a cataract — you have other eye conditions that limit your vision, such as macular degeneration or advanced glaucoma, removing the cataract may not improve vision, and cataract surgery may provide disappointing results.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

The only effective treatment for cataracts is surgery to remove the clouded lens, which usually includes replacing the lens with a clear lens implant. Sometimes cataracts are removed without reinserting implant lenses. In such cases, vision can be corrected with eyeglasses or contact lenses. Cataract surgery is successful in about 95 percent of all cases.

In the past, people were advised to wait until their vision had deteriorated to about 20/200, which would seriously impact their vision. Today, because surgical techniques have improved and the risks from cataract surgery are much lower, surgery is generally recommended when cataracts begin to affect your quality of life or interfere with your ability to perform normal daily activities.

Surgery is done on only one eye at a time. It's generally done on an outpatient basis, usually with local anesthesia. Recovery is fast. You can often resume your normal daily activities beginning the night of your surgery. You may be able to start driving again the day after surgery, after your postoperative checkup.

Cataracts can't be cured with medications, dietary supplements, exercise or optical devices. In the early stages of a cataract when symptoms are mild, a good understanding of the condition and a willingness to adjust your lifestyle can help. Some self-care approaches, such as using a magnifying glass to read or improving the lighting in your home, may help you deal with the effects of having a cataract.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

You can try a few simple approaches to deal with symptoms of cataracts until you decide to have surgery:

• If you have eyeglasses or contact lenses, make sure they're the most accurate prescription possible.
• Use a magnifying glass to read.
• Improve the lighting in your home with more or brighter lamps, for example, lamps that can accommodate halogen lights or 100- to 150-watt incandescent bulbs.
• When you go outside during the day, wear sunglasses to reduce glare.
• Limit your night driving.

Self-care measures may help for a while, but as the cataract progresses, your vision may deteriorate further. When vision loss starts to interfere with your everyday activities, consider cataract surgery.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.

Regular eye exams remain the key to early detection. If you're over age 65, schedule eye exams at least every other year. Although most cataracts occur with age and can't be avoided altogether, you can take steps to help slow or possibly prevent the development of cataracts:

• Don't smoke. Smoking produces free radicals, increasing your risk of cataracts.
• Eat a balanced diet. Include plenty of fruits and vegetables in your diet. Eating lots of fruits and vegetables may have a modest effect in preventing cataract development, though this hasn't been definitively proved.
• Protect yourself from the sun. Ultraviolet light may contribute to the development of cataracts. Whenever possible, wear sunglasses that block ultraviolet B (UVB) rays when you're outdoors.
• Take care of other health problems. Follow your treatment plan if you have diabetes or other medical conditions. If you have a chronic illness, it's especially important that you take other preventive steps, such as wearing UVB-blocking sunglasses when outdoors and not smoking.

Researchers are continuing to explore new ways to prevent and treat cataracts, such as developing medications that would reduce or eliminate the need for surgery. But, until such a treatment exists, your chances of fully restoring your vision with cataract surgery are excellent if you have no other eye diseases.

©1998-2009 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.