Cataracts are cloudy areas in the eye's lens (the normally transparent structure within the eye that focuses images on the light-sensitive retina). Cataracts happen when certain proteins in the lens form into abnormal clumps. These clumps gradually enlarge and interfere with vision by distorting or blocking the passage of light through the lens. Doctors refer to nuclear, cortical and posterior subcapsular cataracts, depending on the layer of the lens involved.
In many cases, cataracts are age-related, appearing first when a person is in his or her 40s or 50s, but not affecting vision until after age 60. In other cases, cataracts may be related to eye trauma, long-term diabetes, corticosteroid medications or radiation treatments. In infants, cataracts may be congenital (present since birth), occurring as a result of an infection that happened during pregnancy, especially toxoplasmosis, cytomegalovirus, syphilis, rubella or herpes simplex. In infants and young children, cataracts may also be one symptom of a metabolic disease affecting the body's processing of carbohydrates, amino acids, calcium or copper.
Cataracts are the world's leading cause of blindness, accounting for approximately 42 percent of all cases of blindness in all nations. In the United States, most cataracts are age-related, affecting more than half of all Americans older than 65 to some degree. Although the exact cause of age-related cataracts is still being investigated, some scientists suspect that this disorder is linked to chemical changes affecting a class of eye proteins called alpha-crystallins. Current research suggests that alpha-crystallins act as chemical "chaperones," which prevent the abnormal clumping of other types of proteins into cataracts. Inactivation of alpha-crystallins due to age-related exposure to oxidizing agents or ultraviolet light, or to very high levels of blood sugar (in diabetics), may make it possible for cataracts to form.
Cataracts typically cause no symptoms until they have grown large enough to interfere significantly with the passage of light through the lens. Once symptoms of cataracts develop, they may include:
- cloudy or blurry vision;
- double vision (diplopia) ;
- a sense that colors appear faded;
- seeing halos around lights;
- an increased sensitivity to glare; and
- a distortion of vision that makes objects appear as if you're looking at them through a veil.
Your doctor will suspect cataracts based on your age and medical history (diabetes, use of prescription corticosteroids) and on your symptoms.
Your doctor can make the diagnosis of cataracts by dilating (widening) your pupil with medication and examining your eye directly using an ophthalmoscope and a slit lamp. You will also have a visual acuity test, a test that uses an eye chart to check the effect of the cataract on your vision.
Cataracts are long-term problems. In most patients, their effect on vision increases with time.
In general, there is currently no way to prevent age-related cataracts; however, people with diabetes may decrease their risk of developing cataracts by tightly controlling their blood sugar levels. To help prevent infection-related congenital cataracts, women should check with their doctors about their need for rubella immunization before becoming pregnant. Women who are already pregnant should see their obstetricians regularly for prenatal care.
Cataract surgery is almost never an emergency. The decision to have surgery depends on the degree to which your vision in impaired, balanced by the small risk that surgery entails. Although some persons with cataracts find that their vision improves by using eyeglasses, magnifying lenses or stronger lighting, the only real way to cure cataracts is by surgery. If cataracts affect both eyes, each eye operation is scheduled and performed separately. Current surgical options include:
- Extracapsular cataract extraction. In this procedure, the lens is either broken up using sound waves (a process called phacoemulsification, or phaco), then extracted through a tiny hollow tube, or it is removed in one piece. The normal lens capsule surrounding the lens is left intact.
- Intracapsular cataract extraction. In this technique, both the lens and the lens capsule are removed. This technique is now performed only in rare cases.
Once the lens is removed, it may be replaced by one of three options:
- An intraocular lens (a plastic lens placed in the eye during cataract surgery);
- A contact lens; or
- Special cataract glasses with very powerful magnification.
Currently, about 90 percent or more of patients use an intraocular lens.
Call your doctor whenever you have trouble seeing clearly. If you are older than 40, schedule an eye examination with your doctor every two years, even if you have not noticed any change in your vision.
Cataract surgery improves the vision of 95 percent of patients who have it. In those patients who have intraocular lens replacements, 90 percent have 20/40 vision or better. In some patients who have had extracapsular surgery, part of the lens capsule eventually becomes cloudy, causing a condition called an after-cataract. This can be corrected with laser surgery, usually as an outpatient.
For more information about cataracts, you can contact:
National Eye Institute
2020 Vision Place
Bethesda, MD 20892-3655
The National Eye Institute is part of the National Institutes of Health. The National Eye Institute also offers a list of national organizations that are related to eye health, which is available at http://www.nei.nih.gov/health/organizations.htm.
Wilmer Eye Institute
Johns Hopkins Hospital
600 N. Wolfe St.
Baltimore, MD 21287
Phone: (410) 955-5080
American Academy of Ophthalmology
P.O. Box 7424
San Francisco, CA 94120-7424
Phone: (415) 561-8500