A new study shows that metformin can result in a reduced risk of developing glaucoma by as much as 21% in diabetes patients.

Researchers found that taking the standard dose of 2g/day over the course of two years resulted in a 21% decrease in their risk of developing glaucoma which was also true after accounting for reduced blood glucose levels. The mechanism by which metformin may reduce this risk is not yet known.

Researchers looked at data on over 150 016 patients with diabetes mellitus, 5893 (3.9%) developed Open Angle Glaucoma(OAG). After adjusting for confounding factors, those prescribed the highest quartile of metformin hydrochloride (>1110 g in 2 years) had a 25% reduced OAG risk relative to those who took no metformin (hazard ratio = 0.75; 95% CI, 0.59-0.95; P = .02). Every 1-g increase in metformin hydrochloride use was associated with a 0.16% reduction in OAG risk (adjusted hazard ratio = 0.99984; 95% CI, 0.99969-0.99999; P =  .04), which predicts that taking a standard dose of 2 g of metformin hydrochloride per day for 2 years would result in a 20.8% reduction in risk of OAG. After accounting for potential confounders, including metformin and diabetic medications, the risk of developing OAG was increased by 8% (hazard ratio = 1.08; 95% CI, 1.03-1.13; P = .003) for each unit of increase in glycated hemoglobin level.

This study suggests that metformin may be affecting OAG risk on multiple levels, some involving improved glycemic control and some involving mechanisms outside glycemic control such as neurogenesis, inflammatory systems, or longevity pathways targeted by caloric restriction mimetic drugs. If confirmed by prospective clinical trials, these findings could lead to novel treatments for this sight-threatening disease.

Editor's note: This study does not mean that all patients should be on high doses of metformin to prevent loss of vision. It is just an epidemiological observation. The study reinforces the importance of glucose reduction in diabetes since there was 8% increase in development of open angle glaucoma with every 1% increase in A1c.

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