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Cataracts result from protein deposits that accumulate within the lens. These deposits disperse light in much the same way cracks in a window might splinter sunlight shining through. The fragmented light creates areas of accentuated brightness, causing the halos and sensitivity to lights at night. The opacity of the cataract interferes with the refractive function of the lens, causing blurry or hazy vision. The yellow or gray discoloration of the lens common with mature or “ripe” cataracts filters the lightwaves that enter the EYE, particularly affecting those in the spectrum of blue.
The location of the cataract on the lens determines the nature and extent of VISION IMPAIRMENT.
Causes of Cataract and Types
Most cataracts develop as a function of aging. Protein structures within the body, including the lens of the eye, begin to change. The lens becomes less resilient. Such changes make it easier for proteins to clump together, forming areas of opacity that eventually form cataracts. Nuclear cataracts form in the nucleus (gelatinous center) of the lens and are the most common type of age-related cataract. Cortical cataracts form in the cortex, or outer layer, of the lens and often do not affect vision.
Infants may be born with cataracts. A congenital cataract affecting only one eye typically is idiopathic (without identifiable cause); congenital cataracts affecting both eyes often suggest genetic disorders such as DOWN SYNDROME. A congenital cataract that is in the line of vision (on the visual axis) can cause significant vision impairment or blindness because the pathways for vision develop in the infant’s first few months of life. Ophthalmologists usually remove such cataracts as soon as possible. Other congenital cataracts may be small and located so they are inconsequential to vision; ophthalmologists generally take an approach of watchful waiting with these.
Cataracts of diabetes
GLUCOSE, which can be present in high blood levels with DIABETES, interacts with the protein structure of the lens, causing protein clumping. People who have type 1 (INSULIN-dependent) diabetes are at greatest risk for cataracts of diabetes, which often develop at a young age. People who have type 2 diabetes or insulin resistance also are at increased risk. Developing cataracts account in part for the vision disturbances that are among the symptoms of diabetes. Treatment for cataracts of diabetes is the same as for age-related cataracts.
Symptoms of Cataract and Diagnostic Path
Because cataracts develop slowly, symptoms become gradually noticeable. Symptoms usually affect only one eye (though cataracts may develop concurrently in both eyes) and may include
- blurry or hazy vision
- double vision
- halos around lights at night
- difficulty seeing at night
- colors appearing faded or dull, or difficulty perceiving shades of blue and purple
Gradual loss of vision at middle age and beyond may be a symptom of AGE-RELATED MACULAR DEGENERATION (ARMD) or GLAUCOMA. Untreated, these conditions result in significant and permanent vision impairments. Any decrease in vision requires an ophthalmologist’s or optometrist’s prompt evaluation.
The ophthalmologist can see cataracts during OPHTHALMOSCOPY, a painless procedure for examining the interior of the eye.
Cataract Treatment Options, Surgery and Outlook
CATARACT EXTRACTION AND LENS REPLACEMENT is the treatment of choice for nearly all cataracts. There is no element of time-sensitivity for the surgery. Though VISUAL ACUITY will progressively deteriorate as the cataract enlarges, there is no permanent harm to vision by waiting to extract the cataract. Following cataract surgery, more than 90 percent of people experience vastly improved vision. Some people who are unable to receive an IOL because of other eye conditions will need to wear a special contact lens or eyeglasses to carry out the refractive functions of the extracted lens. Nearly everyone will still need reading glasses to accommodate PRESBYOPIA.
Risk Factors and Preventive Measures
Cataracts are primarily a consequence of aging. Cataracts also can develop as a SIDE EFFECT of longterm STEROID use (therapeutic or performance enhancing). Cigarette smoking, excessive ALCOHOL consumption, and extended exposure to sunlight (ultraviolet rays) are among the lifestyle factors associated with early or accelerated cataract development. There are no known methods for preventing cataracts.