Risk factors

Cigarette smoking, medications such as corticosteroids, eye injuries, sunlight, diabetes, and even obesity can increase the risk of cataracts. Also, about 50 percent of people ages 65 to 74 and 70 percent of those 75 and older have cataracts.

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Cigarette smoking is associated with an increased risk of cataracts. It is not clear why cigarette smoking has an adverse effect on the lens. One possibility is that smoking might reduce blood levels of nutrients required for lens maintenance.

Long-term use of corticosteroids, especially at high doses, is the most common drug-related cause of cataracts. In one study of individuals taking oral prednisone for prolonged periods, cataracts developed in 11 percent of those taking less than 10 milligrams a day, in 30 percent of those taking 10 to 15 mg a day, and in 80 percent of those taking more than 15 mg a day. Short-term use of oral corticosteroids is unlikely to lead to cataracts.

Inhaled corticosteroids also can raise the risk of cataracts. In one study, people who had used inhaled corticosteroids had a 50 percent greater prevalence of nuclear cataracts and a 90 percent greater prevalence of posterior subcapsular cataracts (in the rear of the lens capsule) than those who had not used inhaled corticosteroids. These results may cause concern for people with asthma, who often rely on inhaled corticosteroids to treat their condition. However, the benefits of inhaled corticosteroids for asthma outweigh the long-term risk of cataracts, which are treatable.

Cataracts can also develop from applying topical corticosteroids to the eyelids or using corticosteroid-containing eyedrops (though the more common side effect is elevated intraocular pressure, which may lead to glaucoma). To reduce the chance of these adverse effects, topical corticosteroids applied to the eye and corticosteroid-containing eyedrops should be used only under the supervision of an ophthalmologist.

Blunt trauma to the eye or damage to the eye from alkaline chemicals can cause opacification of the lens, either immediately or later on. Rapid cataract formation commonly occurs after a penetrating eye injury.

Population studies have shown that prolonged exposure to the ultraviolet radiation in sunlight more than doubles the risk of cortical cataracts. In one study, the more sunlight exposure, the higher the risk of cortical cataracts. However, the study found that nuclear cataracts were not linked to sunlight exposure. Ionizing radiation (from X-rays, for example) also can cause cataracts.

People with diabetes are at increased risk for cataracts, particularly the posterior subcapsular type, and these cataracts tend to occur at an earlier age in people with diabetes than in the general population. Some evidence indicates that the accumulation of sorbitol (a sugar formed from glucose) in the lens promotes cataract formation in people with diabetes.

Excess weight also may increase the odds of developing cataracts. Although the reason for the link between obesity and cataracts is unclear, it is thought that a low-calorie intake may reduce cataract formation by decreasing blood glucose levels or improving the antioxidant properties of the blood.