Feb. 29 (HealthDay News) -- Fasting blood sugar levels are typically used to diagnose diabetes, however, a common complication of the disease that can lead to blindness begins at blood sugar levels below what is considered diabetic, Australian researchers report.

Retinopathy is a vascular condition where the small blood vessels in the eye become damaged; other complications of diabetes include heart, kidney and circulatory problems.

"Retinopathy, which is one of the complications traditionally associated with diabetes, occurs at fasting glucose levels below the threshold that is used to define diabetes," said lead researcher Dr. Tien Y. Wong, chairman of the Department of Ophthalmology at the University of Melbourne.

In the study, Wong's team analyzed three studies that looked at retinopathy among 11,405 people. The report was published in the March 1 issue of The Lancet.

The researchers found that the overall prevalence of retinopathy ranged from 9.6 percent to 15.8 percent in the general population. In addition, they didn't find evidence of a particular blood glucose level that would indicate the presence of retinopathy. In fact, 60 percent of retinopathy cases were missed by the current threshold for diabetes diagnosis, which is 7.0 mmol/L.

The finding suggests that eye damage happens much earlier and at lower blood sugar levels than what is currently used to pinpoint the presence of diabetes, Wong said. "This suggests that diagnostic threshold may have to be revised, so that we can pick up more people who are at risk of eye and other complications," he noted.

In addition to retinopathy, signs of cardiovascular disease also appear to develop at glucose levels below those defined as diabetes, Wong said.

One expert agrees that fasting blood sugar levels may not be the best way of diagnosing diabetes and those at risk for diabetes.

"It is becoming more common that studies are showing that a fasting blood sugar value is not necessarily the best way to judge diabetes or diabetes control," said Dr. Stuart Weiss, an endocrinologist at New York University Medical Center.

Weiss noted that right now there is no other marker for diabetes. However, many new studies point to the use of blood sugar levels after eating as being better markers for risk, he said.

"Fasting blood sugar is not all that helpful," Weiss said. "The problem is that a lot of our thinking is based on fasting. That's an issue we need to focus in on," he said.

SOURCES: Tien Y. Wong, M.D., M.P.H., Ph.D., professor and chairman, Department of Ophthalmology, The University of Melbourne, Australia; Stuart Weiss, M.D., endocrinologist, New York University Medical Center, and clinical assistant professor, NYU School of Medicine, New York City; March 1, 2008, The Lancet