A cataract is a clouding of the lens in the eye. The lens, found behind the iris and the pupil, focuses light on the back of the retina. Cataracts differ by type and cause. More than 50 percent of people over age 80 either have a cataract or have had cataracts surgically removed, according to 2010 information from the National Eye Institute.
Types
Nuclear cataract, the most common type of cataract, is usually associated with aging. Nuclear cataracts form in the center of the lens, which becomes hard and yellow as the cataract progresses. Posterior subcapsular cataracts, often associated with diabetes or steroid use, start at the back of the lens. Cortical cataracts start at the outside of the lens and develop spokes which move inward toward the center of the lens. Diabetics often form cortical cataracts, All About Vision explains.
Causes
Cataracts are also classified by cause. Classifications by cause include age-related, secondary, congenital and radiation. Secondary cataracts arise from diseases such as diabetes, glaucoma, steroid use, or after eye surgery. Congenital cataracts are present at birth and occur in one out of every 2,000 births, according to 2002 information from Dr. Fouad Tayfour of the Windsor Laser Eye Institute. The main reasons these occur are usually the child has an associated syndrome, or they may be inherited. One- third are due to undetermined causes Traumatic cataracts occur after trauma to the eye, including surgery. Radiation cataracts, a type of trauma cataract, occur after certain types of radiation exposure.
Symptoms
Symptoms of cataracts in general include blurry or dim vision, night glare and the appearance of halos around objects at night. In addition, nuclear cataracts cause loss of distance vision more than near vision, while cortical cataracts often cause severe loss of both near and distance vision, and often need earlier removal than other types of cataracts. Because nuclear cataracts may improve near vision and reading ability for a short time, they’re said to give temporary “second sight” and the ability to read without glasses until they worsen, according to the Iris Cantor Women’s Health Center of Cornell University.
Grading
The lens is normally clear, making it easy for light to pass through. As a nuclear cataract develops, the lens begins to turn cloudy in certain areas, which may not be very noticeable. As the cataract progresses, the lens turns a yellowish brown. Medical personnel grade nuclear cataracts, the most common type, according to the degree of yellowing and opacity of the lens.
Other types of cataracts are defined by the percentage of the area they obscure, with cortical cataracts defined by the amount of intrapupillary space obscured, and posterior subcapsular cataracts defined by the percentage of the posterior capsule obscured, according to the American Optometric Association.
Treatment
The treatment for any type of cataract is removal when the cataract affects vision. Around three million American have cataract surgery each year, and 90 percent achieve 20/20 to 20/40 vision after surgery, according to 2010 information from the All About Vision website.
