Cataracts

A cataract is a clouding of the normally clear lens of your eye. It's like trying to see through a frosty or fogged-up window. Clouded vision can make it more difficult to read, drive a car or see the expression on a friend's face. Cataracts commonly affect distance vision and cause problems with glare. They generally don't cause pain, double vision with both eyes open or abnormal tearing.

Clouding of the lens is a normal part of getting older. About half of Americans older than 65 have some degree of clouding of the lens. After age 75, as many as 70 percent of Americans have cataracts that are significant enough to impair their vision.

Most cataracts develop slowly and don't disturb your eyesight early on. But as the clouding progresses, the cataract eventually interferes with your vision.

In the early stages, stronger lighting and eyeglasses can help you deal with the vision problems. But at some point, if impaired vision jeopardizes your normal lifestyle, you might need surgery. Fortunately, cataract removal is one of the safest, most effective and most common surgical procedures.

Signs and symptoms

A cataract usually develops slowly and causes no pain. At first, the cloudiness may affect only a small part of the lens and you may be unaware of any vision loss. Over time, however, as the cataract grows larger, it clouds more of your lens. When significantly less light reaches the retina, your vision becomes impaired.

Symptoms of a cataract 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 or in the production of tears. 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 is extremely rare and needs removal as soon as possible.

Causes

A cataract can develop in one or both eyes, and it may or may not affect the entire lens. The lens is located just behind the iris and the pupil. It's shaped like a magnifying glass — thicker in the middle and thinner near the edges. Tiny ligaments, which are bands of tough tissue fiber, hold it in place.

When your eyes work properly, light passes through the cornea and the pupil to the lens. The lens focuses this light, 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 consists of three layers. The outer layer (capsule) is a thin, clear membrane. It surrounds a soft, clear material (cortex). The hard 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. A cataract can form in any part of the lens.

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 yellow or greenish and begins to cloud your vision. As the cataract progresses, the lens may even turn brown. Seeing in dim light and driving at night may be especially troublesome.