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Cataracts

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of cataracts.

Risk Factors

Aging is the primary risk factor for cataracts, but other factors are also involved.

Age

Nearly everyone who lives long enough will develop cataracts to some extent. A major study reported that:

• About 40% of people age 55 - 64 years had some opaque areas in their lenses, and 5% had fully-developed cataracts
• About 70% of people age 65 - 74 years had opaque areas, and 18% had cataracts
• More than 90% of people age 75 - 84 years had opaque areas, and almost 50% had cataracts

One study indicated that posterior subcapsular cataracts are the most common type in people under 70 years old, while nuclear and mixed cataracts are most common in people over age 80. The risk for nuclear cataracts also increases with age.

Gender

Women face a higher risk than men. Women who started menstruating late are at an even higher risk.

Physical Features

Eye Features. People who are nearsighted and those with brown eyes may be at higher than average risk. (Not all studies, however, report a higher risk in people with darker eyes.)

Obesity and Height. Studies are now reporting obesity as a risk factor for cataracts, notably posterior subcapsular cataracts, which form toward the back of the lens. A study of 17,150 people found a specifically higher rate of cataracts in overweight people who are tall and whose fat distribution is primarily in the abdomen.

Ethnicity

A 9-year population study, published in 2004, revealed that African Americans have nearly twice the risk of developing cataracts then whites. Analysis of the 3,000 participants also demonstrated for the first time that the risk of cortical cataracts is 3 times higher in African Americans than Caucasians. Earlier studies also identified a higher cataract risk in the black population, suggesting that it may be due to other medical illnesses, particularly diabetes. It has long been known that African Americans are much more likely to become blind from cataracts and glaucoma than white Americans, mostly due to lack of treatment.

Hispanic Americans are also at increased risk for cataracts. In fact, cataracts are the leading cause of visual impairment among Hispanics. A 2005 study found that cataracts were about 3 times more common in Hispanic patients age 65 - 84 years than in similarly aged white or African Americans. (The study evaluated Hispanic patients of Mexican descent.) As with African Americans, Hispanic patients often face barriers to access to care.

Diabetes and Other Medical Conditions

People with certain medical conditions, notably diabetes, are at high risk for cataracts, either because of a direct effect of the disease, its treatments, or both.

Autoimmune Diseases and Conditions Requiring Steroid Use. Medical conditions requiring high use of corticosteroids (commonly called steroids) pose a particularly high risk. Many of these medical conditions are autoimmune diseases, including rheumatoid arthritis, psoriasis, multiple sclerosis, systemic lupus erythematosus, Behcet's disease, and others.

Diabetes and People with High Blood Glucose Levels. People with diabetes type 1 or 2 are at very high risk for cataracts and are much more likely to develop them at a younger age. They also have a higher risk for nuclear cataracts than nondiabetics. Cataract development is significantly related to high levels of blood sugar (called glycemia), and cataracts in people with diabetes are sometimes referred to as so-called sugar cataracts. Even people without diabetes but with higher-than-normal blood sugar levels are at high risk for cataracts. Some doctors now recommend that children with diabetes undergo an eye exam to check for cataracts at the time they are diagnosed.

Over-Exposure to Sunlight

Exposure to even low-level UVB radiation from sunlight increases the risk for cataracts. A 2003 study published provided new evidence supporting the link between sun exposure and nuclear cataracts. The risk was highest among those who had significant sun exposure at a young age. Additional studies suggesting risk associated with sunlight exposure report:

• The closer people live to the equator the greater the chance for cataracts. As suggested by a study in Southern France, sunlight exposure in these climates also increases the risk for severe cortical or mixed cataracts. In this study, even wearing sunglasses did not reduce the risk for these cataracts, although it did for posterior subcapsular cataracts.
• People whose jobs expose them to sunlight for prolonged periods are at higher risk. People in southern climates whose occupations, such as fishing or oyster farming, exposed them to very intense sunlight were at high risk for all cataracts, including posterior subcapsular cataracts. (People in more northern climates with similar occupations may not have as high a risk.)
• Occupational exposure to very intense artificial light, such as arc welding, increases the risk for cataracts.

Smoking and Alcohol

Smokers. A study of nearly 18,000 doctors showed that those who smoked 20 or more cigarettes a day had approximately twice the risk of developing cataracts. Smokers are at particular risk for cataracts located in the nuclear portion of the lens, which limit vision more severely than cataracts in other sites. Quitting smoking may reverse some of this damage.

Alcohol Users. Chronic drinkers are at high risk for a number of eye disorders, including cataracts. Alcohol has been implicated in cataract development in a number of studies. Wine provided the least risk, and the more moderate the drinking the lower the risk. Alcohol may work directly on the proteins in the lens itself and indirectly by affecting absorption of nutrients important to the lens.

Environmental Toxins

Long-term environmental lead exposure may increase the risk of developing cataracts according to a study published in the Journal of the American Medical Association . Researchers assessed bone lead levels in 795 men aged 60 years and older. Because lead tends to accumulate over time in the skeleton, the researchers measured lead levels in the men’s shin bones. Men with the highest levels of lead were three times more likely to have cataracts than men with the least amount of lead.

Nutrition

A poor diet may deprive the body of amino acids and B vitamins that are essential for eye health. A French study of elderly adults found that lower blood levels of the protein albumin were associated with an increased risk of cataracts.

Other Conditions

Other conditions that can trigger the process leading to cataracts include:

• Physical injury to the eye (such as a hard blow, cut, or puncture)
• Chemical burns
• Electrical shock injuries
• Chronic exposure to intense heat or cold

• Review Date: 3/1/2007
• Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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