A cataract is a clouding of the eye's lens that leads to decreased vision. The lens of the eye focuses an image onto the retina at the back of the eye, where an image is recorded and then sent to the brain.
As the cataract matures, it often causes glare, as well as decreased vision, contrast, and color sensitivity.
Causes
The lens of the eye is made of mostly water and protein. The protein is arranged in a way that keeps the lens clear and lets light pass through it. A cataract forms when some of the protein clumps together and starts to cloud an area of the lens. A cataract won't spread from one eye to the other, although many people develop cataracts in both eyes.
There are several causes of cataracts, including:
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Aging (the most common cause)
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Smoking
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Diabetes
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Infection
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Injury
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Exposure to radiation
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Taking adrenal cortical hormones for a long time
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Excessive exposure to sunlight
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Birth defect
Risk Factors
A risk factor is something that increases your chance of getting a disease or condition.
Symptoms
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 worsen as the cataract grows. Because the decrease in vision is gradual, many people do not realize that they have cataracts until discovered during an otherwise routine eye examination.
Symptoms include:
These symptoms can also be a sign of other eye problems. If you have any of these symptoms, check with your eye care professional immediately.
Diagnosis
Although you might think you have a cataract, the only way to know for sure is by having an eye examination. To detect a cataract, an ophthalmologist or optometrist examines the lens and may do other tests to learn more about the structure and health of your eye.
A comprehensive eye examination usually includes:
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Visual acuity test – an eye chart test that measures how well you see at various distances
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Pupil dilation – the pupil is widened with eyedrops to see more of the lens and retina
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Tonometry – a standard test to measure fluid pressure inside the eye; increased pressure may be a sign of glaucoma
Treatment
For an early cataract, vision may improve by using different eyeglasses, magnifying lenses, or stronger lighting. If these measures don't help or if vision loss interferes with your everyday activities, such as driving, reading, or watching TV, surgery is the only effective treatment.
In most cases, waiting until you are ready to have cataract surgery will not harm your eye. If you have cataracts in both eyes, the doctor will usually not remove them both at the same time. After the cloudy lens is removed, the surgeon places an intraocular lens (IOL) in its place. An IOL is a clear lens that requires no care and becomes a permanent part of your eye. After cataract surgery, almost everyone needs reading glasses and many people need glasses for distance. There is a new option, multifocal intraocular lenses, which focus distance and near in the same lens. Many patients who receive a multifocal intraocular lens see well at both distance and near without glasses.
An ophthalmologist performs cataract surgery. Although every surgery has risks, the majority of patients who have cataract surgery have better vision afterward.
Prevention
It is not yet clear how to prevent cataracts, although not smoking and consuming antioxidants may help. It is also important to get a comprehensive eye examination regularly. But since vision problems increase with age, if you are over age 60, you should have an eye examination at least once every two years.
RESOURCES:
American Academy of Ophthalmology
http://www.aao.org
National Eye Institute, NIH
http://www.nei.nih.gov
References:
National Institutes of Health. Ophthalmic Genetics Newsletter. 2000 Summer;1(2).
National Institutes of Health website. Available at: http://www.nih.gov/.
