Cataract

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

A clouded lens blocks light from entering the eye. Most cataracts grow slowly until they cloud the entire lens, causing progressive, painless vision loss.

Cataracts are the most common cause of reversible vision loss among older people in the United States. The likelihood of developing a cataract continues to rise with every passing year—it does not level off. Fortunately, vision loss caused by cataracts is usually reversible with surgery.

Causes

The cause of cataracts among older people is mostly unknown. People with dark eyes, those who have had prolonged exposure to bright sunlight, those with poor nutrition, and past or present smokers are more likely to develop them. Also at increased risk are people with diabetes and those who have had other eye diseases or an eye injury. Long-term use of corticosteroids and exposure to x-rays (such as with radiation therapy to the eye) increase the risk as well. People who have had a cataract in one eye are more likely to develop one later in the other eye. Sometimes cataracts develop in both eyes at the same time.

Symptoms and Diagnosis

The first symptom of a cataract is often blurred vision. Sometimes glare is the initial symptom. Reading may become difficult because of a worsening ability to distinguish between the light and dark of printed letters on a page. Colors may seem more yellow and less vibrant. The person may see rings of light around objects (halos) or glare or, less commonly, two images of one object (double vision). The way in which vision is changed by a cataract depends on the intensity of light entering the eye and on the location of the cataract. Occasionally, a cataract temporarily refocuses light and improves vision when near objects are viewed. This phenomenon, called second sight, allows some people to read the newspaper without their reading glasses. Eventually, however, the cataract grows denser. It then blocks light from entering the eye and impairs vision.

See the figure How Cataracts Affect Vision.

A general doctor may diagnose a cataract on examining the eye. However an eye doctor (ophthalmologist) must evaluate the cataract to help determine its specific effects on vision and plan treatment.

Prevention

Some evidence suggests that cataracts may be prevented with consistent use of sunglasses that protect the eyes from sunlight and ultraviolet (UV) light. Prevention of cataracts may also be aided by eating a diet rich in carotenoids (which are substances present in vegetables such as spinach and kale), vitamin C, and vitamin A. For people with diabetes, keeping blood sugar (glucose) levels as close to normal as possible helps prevent cataracts. People who are taking corticosteroids for extended periods might discuss with their doctor the possibility of using a different drug.

Treatment

Cataracts usually require no treatment until vision is significantly impaired. Eyeglasses and contact lenses may improve a person's vision, as may wearing sunglasses that block UV light (sunglasses with polarized lenses). Avoiding lighting that shines directly in the eyes and using lighting that brightens without shining in the eyes (for example, using a lamp that provides over-the-shoulder lighting while reading) may help.

Beyond these measures, surgery is the only treatment that provides a cure. However, surgery should be performed only when visual impairment is making the person feel unsafe, uncomfortable, or unable to perform daily tasks. Having cataracts removed sooner usually offers no advantage. Cataracts are sometimes removed earlier if they prevent a doctor from examining the back of the eye in people at risk of vision loss from glaucoma, diabetes, or age-related macular degeneration.

Cataract surgery can be performed at any age and is generally safe even for people with chronic diseases, such as coronary artery disease and diabetes. During surgery, the doctor usually makes a small incision in the eye, breaks up the lens using ultrasound (phacoemulsification), and removes all of the pieces. The tissue surrounding the lens (the lens capsule) is left in place in the eye. The surgeon usually implants an artificial lens (intraocular lens). The artificial lens, which is supported and held in position by the lens capsule, restores the eye's ability to focus images on the retina. If an artificial lens cannot be implanted safely, the person must wear thick eyeglasses or contact lenses to substitute for the eye's natural lens.

Complications after cataract surgery are infrequent. An infection or serious bleeding may develop in the eye, which can lead to partial or complete vision loss. Eye pressure may become too high (glaucoma), or the lens implant can become displaced. The central and most sensitive part of the retina (macula) can become swollen or detached. Rarely, an existing retinal disorder, such as diabetic retinopathy, may progress after cataract surgery, which can lead to further vision loss.

In about one third of people who have had cataract surgery, the remnants of the lens capsule become cloudy, impairing vision. Vision can be restored with laser therapy.

Outlook

Many people notice improved vision within a few weeks after cataract surgery. Almost everyone who has undergone this surgery needs eyeglasses to see near objects (for example, for reading), and most people need weak eyeglasses to reach their potential for seeing far objects. People with cataracts in both eyes can further improve their vision by having a cataract removed from the other eye several months after the first eye has healed.