Nearly 30 percent of U.S. adults with diabetes are estimated to have diabetic retinopathy, with about 4 percent having a vision-threatening form of the condition, according to a study in theJournal of the American Medical Association.

Diabetic retinopathy, which is damage to the retina caused by complications of diabetes mellitus, is the leading cause of new cases of legal blindness among adults 20 to 74 years of age in the U.S.

Researchers conducted a study consisting of more than 1,000 diabetics between 2005 and 2008 to determine the most recent prevalence and risk factors of diabetic retinopathy in the U.S. population among those over 40 years old.

The current findings represent an increase of about 40 percent for diabetics who have the condition, and an increase of two and a half times for diabetics who have a vision-threatening case of it compared to estimates from the last similar study, conducted from 1988 to 1994.

They also found that the independent risk factors for diabetic retinopathy include being male, higher hemoglobin A1c level, longer diabetes duration, use of insulin and higher systolic blood pressure.

Researchers say that this information is important for early detection and treatment of diabetic retinopathy.

Individuals with diabetes are advised to control their blood sugar, cholesterol and blood pressure to help prevent complications such as diabetic retinopathy.