Here is more evidence that uncontrolled blood sugar (hyperglycemia) increases the risk of diabetic retinopathy (blindness). Individuals who have poorly controlled type 1 or type 2 diabetes may be at greater risk of developing retinopathy, according to a new study from a team of French researchers. They found that persistently high levels of blood sugar are a strong indicator of future retinopathy risk.
In a cohort study, the risk of the condition shot up markedly when fasting plasma glucose and glycated hemoglobin (HbA1c) reached levels that are used to indicate diabetes risk, according to Beverley Balkau, PhD, of the Institut National de la Santé et de la Recherche Médicale in Villejuif, France, and colleagues.
The finding allows physicians to set threshold values that define patients at risk of the eye condition, they argued in the February issue of Archives of Ophthalmology. They said the information helps clear up some debate over the role that blood sugar levels play in the development of retinopathy and could provide medical professionals with a way of measuring a patient’s risk for the condition.
For the study, Balkau and colleagues studied more than 700 men and women taking part in the DESIR study, which enrolled volunteers ages 30 to 65 in western France from 1994 to 1996. At the outset, doctors examined participants’ retinas and took blood sugar readings. The individuals were then followed for a period of ten years.
The goal was to study the frequency of retinopathy in individuals 10 years after measuring baseline levels of fasting plasma glucose and HbA1c and to evaluate positive predictive values for retinopathy at various levels of the glycemic variables.
After a baseline health exam, all participants were asked to return for subsequent examinations three, six, and nine years later. Those who were diagnosed with diabetes or who had had a fasting glucose level of at least 126 mg/dL at any point during the study were asked to undergo testing for retinopathy using a nonmydriatic digital retinal camera.
For comparison, two groups of matched participants also had the retinal exam ‒ those who had had an impaired fasting glucose level (from 110 through 125 mg/dL) at any time during the study and those whose glucose levels had always been below 110 mg/dL.
By the end of the study period, the researchers noted a strong correlation between initial blood sugar readings and the development of retinopathy. Participants with the condition had 22 percent higher fasting blood sugar levels and 12 percent higher HbA1c levels at the start of the study compared to participants who did not develop retinopathy.
All told, the researchers found 44 participants with retinopathy, including 19 of 237 in the diabetes group, another 19 of 246 with impaired glucose levels, and six of 249 in the normal glucose group.
Those with retinopathy had higher baseline fasting glucose and HbA1c levels on average — 106 versus 130 mg/dL and 6.0% versus 6.4%, respectively (P<0.001).
And a higher percentage were treated for hypertension ‒ 36.4% of those with retinopathy compared with 19.6% (P=0.008), and they had a trend toward higher systolic blood pressure.
Analysis also showed that:
• Fasting plasma glucose levels of 108 and 116 mg/dL had positive predictive values of 8.4% and 14.0%, respectively, for retinopathy.
• HbA1c levels of 6.0% and 6.5% had positive predictive values of 6.0% and 14.8%, respectively.
Because of the sharp increase, they argued, the lower levels of each marker should be used as thresholds to identify those at risk of retinopathy 10 years down the road. “We propose that thresholds of 108 milligrams per deciliter for fasting plasma glucose concentration and 6.0 percent for HbA1c level could be used to define those who are at risk of retinopathy,” they wrote.
Balkau and colleagues noted that the study’s strengths included a large sample size and long follow-up.
However, they cautioned that the study participants were self-selected individuals who volunteered for the study after a free health checkup and the sample size of those with retinopathy was small, allowing evaluation only of risk factors strongly associated.