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THURSDAY, April 16 (HealthDay News) -- The drug calcium dobesilate does not prevent the development of blindness-causing macular edema in people with diabetes who have mild-to-moderate diabetic retinopathy, a new study has found.

About 50 percent of people who have type 1 diabetes and 30 percent of those with type 2 diabetes develop retinopathy, which is damage to the retina caused by diabetes-related complications. Clinically significant macular edema (CSME) occurs when diabetic retinopathy progresses.

When this happens, fluid and protein deposits accumulate near or at the macula, the central area of the retina, causing it to thicken and swell, according to background information in a news release from The Lancet. The results of the study are in this week's issue of the journal.

The multi-center study included 635 people with type 2 diabetes and mild-to-moderate diabetic retinopathy who were randomly selected to take either calcium dobesilate or a placebo.

CSME developed in 86 of the 324 people who took calcium dobesilate and in 69 of the 311 who took the placebo. The researchers determined that people who took the drug were 32 percent more likely to develop CSME than those who took the placebo.

"Our findings showed that calcium dobesilate could neither prevent occurrence of CSME nor reduce probability of developing CSME during the five-year follow-up period" in the participants, concluded Dr. Christos Haritoglou, of Ludwig-Maximilians-University in Munich, Germany, and his colleagues.

An accompanying commentary stressed the need to "distinguish between the prevention of retinopathy and the prevention of diabetic blindness." It was written by Dr. Anna B. Einarsdottir and Dr. Einar Stefansson of the University of Iceland and Landspitali, National Hospital, in Reykjavik, Iceland.

"Diabetic blindness can be reduced or prevented without reducing retinopathy," they said. "Systemic screening for diabetic retinopathy and preventive laser treatment for those who develop macular edema or proliferative retinopathy reduces the rate of blindness to about 0.5 percent in the diabetic population, regardless of the prevalence of retinopathy."

More information

The U.S. National Eye Institute has more about diabetic eye disease.