Last updated: 02/17/2009

Cataract extraction is one of the most frequently performed surgical procedures in industrialized countries. It is estimated that 300,000–400,000 cases of visually disabling cataracts occur each year in the United States alone, and that between 1...

and 1.5 million cataract extractions are performed annually in the United States. This frequency reflects the importance of cataracts as a
major public health problem. The World Health Organization (WHO) estimated in 1997 that cataracts are responsible for 50% of cases of blindness around the world, or 19 million people. By 2020, that figure is expected to rise to 50 million. More recent publications estimate that 1.2% of the general population of Africa is blind, with cataracts responsible for 36% of these cases of blindness.

About one person in every 50 in the general American population will eventually have to have a cataract removed. It is difficult, however, to compare the rates of cataract formation among various subgroups because present published studies use a number of different grading systems for defining and detecting cataracts. In addition, the elderly are often under-represented in general population studies even though age is the greatest single risk factor for cataract development. Three recent research projects carried out in the United States, Australia, and England, respectively, reported that 50% of people over the age of 60 have some degree of cataract formation, with the figure rising to 100% for those over 80. As of 2003, little conclusive information is available regarding the incidence of cataracts in different racial and ethnic groups in the United States.

A variety of risk factors in addition to age have been associated with cataracts, but their precise significance is debated among researchers:

• Genetic factors. Twin studies show that the identical twin of a patient with a nuclear cataract has a 48% chance of developing one.
• Sex. Women are slightly more likely than men to develop cataracts. One American study found that 53.3% of women over 60 had nuclear cataracts compared to 49.7% of the men; 25.9% of the women had cortical cataracts versus 21.1% of the men.
• Exposure to ultraviolet radiation. Cortical cataracts are more likely to develop in people with frequent exposure to sunlight; however, nuclear cataracts are not related to sun exposure.
• Smoking. People who smoke more than 25 cigarettes per day are three times as likely as nonsmokers to develop nuclear or PSC cataracts. Smoking does not appear to be related to cortical cataracts.
• Alcohol consumption. Heavy drinking has been reported to increase the risk of developing all three types of cataracts.
• Diabetes. Patients with diabetes are at increased risk of developing all three types of cataracts.
• Use of steroid medications. PSC cataracts are known to be induced by steroids, even though they represent less than 10% of all cataracts.
• Socioeconomic status (SES). People with college or professional-school education have lower rates of cataract formation than people who did not finish high school, even attempting to correct for environmental and nutritional factors. There is, however, no obvious biochemical or medical explanation for this correlation, and some researchers treat it with caution.
• Chronic dehydration, diarrhea, and malnutrition. Studies carried out in India indicate that severe malnutrition or repeated episodes of diarrhea in childhood carry a three-to fourfold increase in risk of developing cataracts in later life. It is not yet known, however, whether this statistic would hold true for people in other countries.