Use of CGM Linked to Lower Risk of Retinopathy in Type 1 Diabetes

In patients with type 1 diabetes, use of continuous glucose monitoring (CGM) devices — alone or with insulin pumps — was associated with lower odds of developing diabetic retinopathy and proliferative diabetic retinopathy, according to a retrospective cohort study.

In a multivariable logistic regression analysis, use of CGM devices was associated with lower odds of diabetic retinopathy (OR 0.52, 95% CI 0.32-0.84, P=0.008) and proliferative diabetic retinopathy (OR 0.42, 95% CI 0.23-0.75, P=0.004) compared with no use, reported Risa M. Wolf, MD, of Johns Hopkins University School of Medicine in Baltimore, and colleagues in JAMA Network Open.

In a longitudinal analysis of patients without baseline proliferative diabetic retinopathy, 21.8% had progression of diabetic retinopathy during the 8-year study.

The positive effect likely isn’t entirely produced by glycemic control via CGM since the researchers controlled for HbA1c, co-author Nestoras Mathioudakis, MD, MHS, also of Johns Hopkins University School of Medicine, told MedPage Today. Instead, “this is probably being driven by glycemic variability and the percentage of time that you’re staying within a certain range.”

While insulin pump use alone was not linked to diabetic retinopathy (P=0.48), CGM and pump use together were associated with lower odds of proliferative diabetic retinopathy (OR 0.60, 95% CI 0.38-0.94, P=0.03) compared with no CGM or insulin pump use, the researchers reported. Other factors that were associated with diabetic retinopathy development after adjustment were duration of diabetes (OR 1.07, 95% CI 1.04-1.09, P<0.001), other microvascular complications (OR 8.87, 95% CI 5.60-14.06, P<0.001), and mean HbA1c (OR 1.29, 95% CI 1.11-1.50, P=0.001).

It’s not clear why use of insulin pumps alone were not tied to signs of improvement in diabetic retinopathy. However, Mathioudakis said the study’s sample size may have been too limited to accurately reflect their impact.

He noted that the current state of the art is a hybrid, closed-loop CGM-insulin pump device that automatically produces tighter glucose control. It wasn’t available during the 2013-2021 period of the study. “A similar study will need to be done over the next 5 years to really start to look at the impact of people using those newer technologies,” he said.

Could those who used the devices in the study simply be healthier overall or more likely to take care of themselves? Mathioudakis said the researchers tried to control for this possibility by adjusting their analysis for various possible confounders. Notably, 76.8% of white patients had CGM devices (either with or without pumps) versus just 15.9% of Black patients (P<0.001).

“We do expect to see similar findings in type 2 diabetes,” he added.

In an accompanying commentary, Estelle M. Everett, MD, MHS, of the David Geffen School of Medicine at the University of California Los Angeles, wrote that “CGM has a unique advantage that can support the prevention of diabetic retinopathy. This can be particularly beneficial in groups that are at the highest risk for retinal complications.”

“While the findings in the study … suggest CGM could be leveraged to improve retinopathy-related outcomes in these high-risk groups, the literature also describes disparities in CGM use in these very populations,” she noted.

The study authors pointed to a landmark study that showed that nearly half of patients with type 1 diabetes developed diabetic retinopathy over a mean 6.5 years without intensive insulin therapy, and there’s been little research into the effect of CGM devices and insulin pumps on diabetic retinopathy.

However, co-author T. Y. Alvin Liu, MD, of Johns Hopkins University School of Medicine, told MedPage Today that he’s seen signs of “a really profound protective effect” in the clinic.

“Unfortunately, a lot of patients with type 1 diabetes typically present with advanced diabetic retinopathy that’s really difficult to manage,” he said. “However, over the years, we’ve noticed there’s a subset of patients who do extremely well. When I chat with them personally, invariably they’re using some sort of technology such as continuous glucose monitoring or insulin pump.”

As for cost, Wolf told MedPage Today that CGM devices are now standard of care and covered by most insurers. “That really should not be a barrier to get a CGM,” she said.

Liu said he urges patients to use the devices, noting that they often ask, “Does that mean these devices could decrease my chance of going blind?” he said. “And the answer is yes. That is a very encouraging message and motivating message for them to go down this path.”

For this study, Wolf and colleagues included 550 adults (median age 40, 54.4% women, 24.5% Black, 68.4% white) who had type 1 diabetes for a median of 20 years. All were treated at the Johns Hopkins Endocrine and Diabetes Center and the Wilmer Eye Institute in Baltimore.

Among these patients, median HbA1c was 7.8%, and 44% had diabetic retinopathy at some point during the study. CGM devices were used by 62.7% of the study population, insulin pumps by 58.2%, and both by 47.5%.

The authors noted study limitations such as its retrospective nature and possible underestimation of the effect of CGM due to limitations in its use as the technology developed.

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