A cataract is a clouding or opacification of the lens of the eye. The crystalline lens is the driest soft tissue in the body and this trait contributes directly to the transparency of the normal lens. Cataract can occur when some of the protein that makes up the lens begins to clump together. As this phenomenon occurs, it diverts light rays from passing through the lens and focusing clearly on the retina, the light-sensitive tissue lining located in the back of the eye. In its early stages, a cataract may not cause a problem. The cloudiness may affect only a small part of the lens. However, the cataract may progress over time, making it harder to see. As less properly focused light reaches the retina, vision may become dull and blurry.
Although scientists don’t know for sure what causes cataracts, they suspect several factors, including smoking, diabetes, steroid use, diuretic use, and certain major tranquilizers.
Probably the greatest risk factor for cataracts is age. Although age-related cataracts may develop between 40 and 50 years old, vision is usually not affected greatly until after age 60. Another factor may be geography; recent studies have shown that people who live in high altitudes are at higher risk for developing cataracts. In addition, people who spend more time in the sun may develop cataracts earlier than others.
Types According to the National Institutes of Health, there are four types of cataracts:
Age-related cataracts: The majority of cataracts are related to aging.
Congenital cataracts: Some babies are born with cataracts or develop them in childhood. Some congenital cataracts do not affect vision, but others do and need to be removed.
Secondary cataracts: These develop primarily as a result of another disease, such as diabetes.
Traumatic cataracts: Eye that have sustained an injury may develop a cataract immediately following the incident or several years later.
The American Academy of Ophthalmology describes cataracts according to their location on the eye lens:
Nuclear cataract: This is the most common type of cataract and the most common type associated with aging. Nuclear cataracts develop in the center of the lens and can induce nearsightedness—a temporary improvement in reading vision that’s sometimes called “second sight.” Unfortunately, second sight disappears as the cataract progresses.
Cortical cataract: This type initially develops as wedge-shaped spokes in the cortex of the lens, with the spokes extending from the outside of the lens to the center. The spokes interfere with the transmission of light and cause glare and loss of contrast. This type of cataract is frequently developed in people with diabetes, and it may impair vision so significantly that surgery is needed.
Subcapsular cataract: A subcapsular cataract usually starts as a small opacity under the capsule, at the back of the lens. It’s often found in people with diabetes, myopia, or retinitis pigmentosa and in those taking steroids.
Tests and Procedures
Cataracts can be diagnosed through a visual acuity test (the common eye chart test), which measures vision ability at various distances, and pupil dilation, in which the pupil is enlarged with eye drops to allow a close-up examination of the retina. Other tests also may be performed to help your eye care professional learn more about the health and structure of your eye.
In its early stages, vision loss caused by a cataract may be aided with the use of eyeglasses, a magnifying glass, or stronger lighting. When these measures no longer help, surgery is the only effective treatment for most people. It’s important to note that a cataract needs to be removed only when vision loss interferes with everyday activities such as driving, reading, or watching television. You and your doctor can make that decision together. Cataract surgery involves removing the cloudy lens and replacing it with an artificial lens implant. It’s one of the safest, most effective, and most common operations performed.
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National Eye Institute. http://www.nei.nih.gov/health/cataract/cataract_facts.asp