In type 2 diabetes patients, this study found no evidence to support a link between metformin use and increased risk of AMD. Photo: McGuff Medical. Click image to enlarge.

In its late stages, age-related macular degeneration (AMD) is a leading cause of sight loss. Previous studies have suggested that metformin—commonly used to treat diabetes patients—may be associated with a reduced risk of developing the condition, but the evidence has been inconclusive. A recent study did not determine a solid association between the medication and the disease.

The researchers investigated the relationship between metformin use and development of AMD among patients with type 2 diabetes. Their analysis included nearly 174,000 individuals ages 40 and older. The exposed group was prescribed metformin, and the unexposed group was prescribed other antidiabetic medications. The exposure status was treated as time varying, collected at three-month intervals.

No evidence was found between metformin use and development of AMD in type 2 diabetes patients. During follow-up, only 3,111 (1.8%) of patients developed AMD. 

Women had a significantly higher risk of developing AMD, as well as those older in age, current and ex-smokers, and those with high HbA1c levels.

There was also evidence of a positive correlation between the degree of oxidative stress and glycated hemoglobin, suggesting that a high HbA1c may accelerate the development of AMD. 

The authors also observed an association between AMD and sight-threatening retinopathy. “This could be the result of misclassification or result from the fact the metabolic stress in the retina increases the risk of both AMD and retinopathy—also supported by the association between increased HbA1c and AMD,” the authors explained. “The role of oxidative stress has long been recognized as a hallmark of the disease pathogenesis of AMD.”

The authors suggest further studies should evaluate whether metformin has an impact on disease progression following a diagnosis of AMD.