A growing body of research about possible health concerns relating to diabetes treatments known as glitazones has now added vision loss as a possible side effect of the drugs, researchers say.

A total of 996 of the 170,000 diabetic patients studied by Dr Donald S. Fong and Dr Richard Contreras developed diabetic macular edema, a condition that can cause vision loss by promoting retinal swelling.

For those taking pioglitazone, marketed as Actos or rosiglitazone, marketed as Avandia, that risk was 2.4 times as great as those on other medications.

Previous research has linked the class to increased heart attack risk, fluid retention and heart failure.

Researchers at Duke University issued a study last year that found healthcare costs for Medicare patients with diabetic macular edema were 31 percent higher over one year, and 29 percent higher over three years when compared to those without the condition.

The Centers for Disease Control report that in 2007, 23.6 million Americans suffered from diabetes, including 10.7 percent of Americans over age 20.