A cataract occurs when the normally clear lens in the eye becomes cloudy. Cataracts are the leading cause of correctable reduced vision worldwide. Most cataracts develop slowly with normal aging. However, cataracts also may be related to genetic diseases and medical conditions such as diabetes. Other factors such as poor nutrition, sun damage, radiation, corticosteroids, smoking, alcohol, eye trauma or other eye surgery may influence cataract formation.
Mild or early cataracts may not impair vision. In some cataracts, new eye-glass prescriptions, brighter lighting or magnifying lenses may overcome the vision losses. When these interventions fail to improve poor vision due to cataracts, surgical removal (extraction) is the generally accepted effective treatment. However, cataract surgery is associated with some risks. The estimated annual costs for outpatient, inpatient and prescription drug services related to the treatment of cataract is USD 6.8 billion.
Antioxidant vitamin supplementation has been studied as a means to prevent the formation or to slow the progression of cataract. Results from observational studies have been inconsistent.
The review authors searched for randomized controlled trials in which supplementation with the antioxidant vitamins beta-carotene (provitamin A), vitamin C and vitamin E was compared to inactive placebo or no supplement. Nine trials involving 117,272 adults of age 35 years or older were included in this review. The trials were conducted in Australia, Finland, India, Italy, the United Kingdom and the United States and were of high methodological quality. The doses of antioxidants given in each trial were higher than the recommended daily allowances. The trials provided no evidence of effect of the antioxidant vitamins beta-carotene, vitamin E and vitamin C given alone or in combination on the incidence of cataract, its extraction or progression and on the loss of visual acuity. Some participants (7% to 16%) on beta-carotene developed yellowing of the skin (hypercarotenodermia).
