The lens is the part of the eye that helps focus light on the retina. The retina is the eye's light-sensitive layer that sends visual signals to the brain. In a normal eye, light passes through the lens and gets focused on the retina. To help produce a sharp image, the lens must remain clear.

The lens is made mostly of water and protein. The protein is arranged to let light pass through and focus on the retina. Sometimes some of the protein clumps together. This can start to cloud small areas of the lens, blocking some light from reaching the retina and interfering with vision. This is a cataract.

In its early stages, a cataract may not cause a problem. The cloudiness may affect only a small part of the lens. However, over time, the cataract may grow larger and cloud more of the lens, making it harder to see. Because less light reaches the retina, your vision may become dull and blurry. A cataract won't spread from one eye to the other, although many people develop cataracts in both eyes.

Although researchers are learning more about cataracts, no one knows for sure what causes them. Scientists think there may be several causes, including smoking, diabetes, and excessive exposure to sunlight.

The most common symptoms of a cataract are:

• Cloudy or blurry vision.
• Problems with light. These can include headlights that seem too bright at night; glare from lamps or very bright sunlight; or a halo around lights.
• Colors that seem faded.
• Poor night vision.
• Double or multiple vision (this symptom often goes away as the cataract grows).
• Frequent changes in your eyeglasses or contact lenses.

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

When a cataract is small, you may not notice any changes in your vision. Cataracts tend to grow slowly, so vision gets worse gradually. Some people with a cataract find that their close-up vision suddenly improves, but this is temporary. Vision is likely to get worse again as the cataract grows.

To detect a cataract, an eye care professional examines the lens. A comprehensive eye examination usually includes:

For an early cataract, vision may improve by using different eyeglasses, magnifying lenses, or stronger lighting. If these measures don't help, surgery is the only effective treatment. This treatment involves removing the cloudy lens and replacing it with a substitute lens.

Cataract removal is one of the most common operations performed in the U.S. today. It is also one of the safest and most effective. In about 90 percent of cases, people who have cataract surgery have better vision afterward.

There are two primary ways to remove a cataract. Your doctor can explain the differences and help determine which is best for you:

A week or two before surgery, your eye care professional will do some tests. These may include tests to measure the curve of the cornea and the size and shape of the eye. For patients who will receive an IOL, this information helps your doctor choose the right type of IOL. Also, doctors may ask you not to eat or drink anything after midnight the morning of your surgery.

When you enter the hospital or clinic, you will be given eye drops to dilate the pupil. The area around your eye will be washed and cleansed.

The operation usually lasts less than 1 hour and is almost painless. Many people choose to stay awake during surgery, while others may need to be put to sleep for a short time. If you are awake, you will have an anesthetic to numb the nerves in and around your eye.

After the operation, a patch will be placed over your eye and you will rest for a while. You will be watched by your medical team to see if there are any problems, such as bleeding. Most people who have cataract surgery can go home the same day. Since you will not be able to drive, make sure you make arrangements for a ride.

It's normal to feel itching and mild discomfort for a while after cataract surgery. Some fluid discharge is also common, and your eye may be sensitive to light and touch. If you have discomfort, your eye care professional may suggest a pain reliever every 4-6 hours. After 1-2 days, even moderate discomfort should disappear. In most cases, healing will take about 6 weeks.

You can quickly return to many everyday activities, but your vision may be blurry. The healing eye needs time to adjust so that it can focus properly with the other eye, especially if the other eye has a cataract. Ask your doctor when you can resume driving.

If you just received an IOL, you may notice that colors are very bright or have a blue tinge. Also, if you've been in bright sunlight, everything may be reddish for a few hours. If you see these color tinges, it is because your lens is clear and no longer cloudy. Within a few months after receiving an IOL, these colors should go away. And when you have healed, you will probably need new glasses.

Sometimes a part of the natural lens that is not removed during cataract surgery becomes cloudy and may blur your vision. This is called an after-cataract. An after-cataract can develop months or years later.

Unlike a cataract, an after-cataract is treated with a laser. In a technique called YAG laser capsulotomy, your doctor uses a laser beam to make a tiny hole in the lens to let light pass through. This is a painless outpatient procedure.

Findings from the NEI-sponsored Age-Related Eye Disease Study (AREDS) showed that high levels of antioxidants and zinc has no significant effect on the development or progression of cataract.

Other research is focusing on new ways to prevent, diagnose, and treat cataracts. In addition, scientists are studying the role of genetics in the development of cataracts.

Although we don't know how to protect against cataracts, people over the age of 60 are at risk for many vision problems. If you are age 60 or older, you should have an eye examination through dilated pupils at least every 2 years. This kind of exam allows your eye care professional to check for signs of age-related macular degeneration, glaucoma, cataracts, and other vision disorders.