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Swinging Light: Back to Basics for Spotting Diabetic Retinopathy

LONDON – Long-established, but often forgotten, primary care tools, including the swinging light test and the lipid-lowering drug fenofibrate, may help detect early worsening of diabetic retinopathy in primary care patients with diabetes who present with vision problems, said GP and diabetes specialist Kevin Fernando at this year’s Diabetes Professional Care conference. 

“If any of your patients with diabetes come in and say, ‘I can’t see very well’ [subacute onset of blurred vison, floaters, or field loss], then take that very seriously because they have a high risk of serious eye disease,” said Fernando. “We need to intervene early to prevent that tragic loss of vision and consider urgent referral.”

He invited delegates to think back to medical school and the swinging light test to detect a relative afferent pupil defect: a difference between the two eyes in response to a light shone in one eye at a time. 

“I’ve started doing this again in recent years for anyone with diabetes who says they have visual symptoms, and I ask you to consider doing this too,” he said. “It’s very easy to do, and a positive test result can signify serious retinal or optic nerve disease.” 

Early worsening of diabetic retinopathy is especially prevalent with the rapid reduction of blood glucose from insulin administration, where HbA1c can drop by 1.5%-2%, said Fernando. He suggested avoiding a large reduction in HbA1c of >22 mmol/mol (2%) in patients with existing diabetic retinopathy. 

Initial data from the SUSTAIN-6 trial had demonstrated an association of semaglutide use with worsening diabetic retinopathy. Fernando said that the worsening of retinopathy was later shown to be associated instead with rapid glucose-lowering in already vulnerable patients.

He went on to reference another recent (September 2023) publication in the journal Diabetes Care that evidenced the early worsening of diabetic retinopathy in people who experience rapid lowering of HbA1c. “We are now in an era of potent antidiabetic drugs, for example tirzepatide, which leads to a 2.2% reduction in HbA1c,” he said. “If in primary care you are considering a high dose of glucose-lowering drug, such as semaglutide or tirzepatide, then be aware of the presence and the degree of any diabetic retinopathy before initiating that drug.”

He stressed that extra caution was necessary if the patient was already taking insulin. “Slow and steady is the preferred way to manage such patients. People with background retinopathy are less concerning—it is those with advanced, proliferative retinopathy.” 

Repurposing Old Methods: “Practice Pearls”

Fernando turned to what he termed “practice pearls” to help primary care doctors manage patients showing early changes in diabetic retinopathy to prevent progression to later stages. He also highlighted how a long-used lipid-lowering agent, fenofibrate, might work for some patients to avoid progression of diabetic retinopathy. 

“We can look at blood pressure, glycaemia, prescribe statins for anyone with retinopathy and diabetes. But interestingly, over the years, there has been mixed evidence about fenofibrate used in these patients,” he said. “In Australia, they found the evidence so compelling that they added an indication for the use of fenofibrate in diabetic retinopathy.” There is no approval for the indication of fenofibrate’s use in diabetic retinopathy in the UK. 

Fenofibrate has been used for more than 20 years to lower lipids. Studies conducted in patients with diabetes suggested that taking fenofibrate may slow down the progression of retinopathy by 30%-40%. However, conclusive information is needed.

The 2006 FIELD study suggested that fenofibrate reduced the need for laser therapy in patients with maculopathy and proliferative diabetic retinopathy. However, no legacy effect was seen once fenofibrate was stopped. 

In June of this year, a Cochrane review found little or no evidence for the use of fenofibrate in diabetic retinopathy, and again concluded no legacy effects when stopped. “Effects were seen in certain subgroups of patients, but they concluded that there was no compelling evidence to date to recommend fenofibrate’s use in diabetic retinopathy,” said Fernando. 

However, he added that, “Within coming months, the LENS study (Lowering Events in Non-proliferative Retinopathy in Scotland) led by the University of Oxford should give a final answer on whether fenofibrate reduces progression.”

“Fenofibrate is known as a lipid-lowering drug with lots of evidence and there is no real downside because it is well-tolerated,” said Fernando. “If I developed diabetic retinopathy, then I’d take fenofibrate. It’s been around for many years.”

Fernando has declared speaker fees from Eli Lilly and Company; and Novo Nordisk. He was speaking at a session sponsored by Embecta.