David Friedman of The Johns Hopkins School of Medicine in Baltimore compared national health examination data from 1999 to 2002 with data from 2005 to 2008.
"Visual impairment that cannot be corrected with glasses increased by about 20 percent over the last six to seven years," Friedman said in a statement. "The only major risk factor for vision loss that increased was diabetes lasting 10 or more years."
More than 14 million people age 12 and older are visually impaired in the United States. Of these cases, 11 million are attributable to refractive error, and are correctable by glasses.
The most common causes of non-refractive visual impairment in the United States are age-related macular degeneration, cataract, diabetic retinopathy, glaucoma and other retinal disorders, Friedman said.
Previous studies have shown that visual impairment is common in people with diabetes.
"The prevalence of diagnosed diabetes has increased among adults in recent years, rising from 4.9 percent in 1990 to 6.5 percent in 1998, 7.9 percent in 2001, 10.7 percent in 2007, and 11.3 percent in 2010," Friedman said.
The risk and potential damage of type 2 diabetes can be controlled with diet and physical activity, Friedman said.
The study was published in the Journal of the American Medical Association.
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