Visual impairment appears to be more common in people with diabetes than in those without the disease, according to a new report.

Approximately 14.6 million Americans had diagnosed diabetes mellitus in 2005 and another 6.2 million had undiagnosed diabetes, according to background information in the article. It is estimated that the number of individuals with diagnosed diabetes will increase to 48.3 million by 2050.

The article appears in the October issue of Archives of Ophthalmology, one of the Journal of the American Medical Association/Archives journals.

"Diabetic retinopathy [damage to the retina caused by diabetes], one of the most common microvascular complications of diabetes, is considered to be one of the major causes of blindness and low vision," the authors write.

Although studies suggest that controlling glucose and blood pressure have reduced the rate of retinal diseases, other ocular conditions suffered by diabetic patients, such as cataract and glaucoma, may increase the risk of visual impairment. Additionally, decreased vision caused by an abnormal shape of the cornea is also common among people with diabetes.

Dr. Xinzhi Zhang and colleagues at the Centers for Disease Control and Prevention used data from the National Health and Nutrition Examination Surveys from 1999 to 2004, which included 1,237 adults with diabetes and 11,767 adults without the disease and also measured their visual acuity before and after optical correction. Participants' vision was tested while they were wearing any glasses or contacts they typically used, and their demographic information was also noted.

An estimated 11 percent of American adults with diabetes had some form of visual impairment (3.8 percent uncorrectable and 7.2 percent correctable), while only 5.9 percent of those without diabetes had some form of visual impairment (1.4 percent uncorrectable and 4.5 percent correctable).

The report also found a strong association between visual impairment and older age, race and ethnicity, lower income and lack of health insurance, all independent of diabetes status.