By Steven Reinberg
People who took the most metformin during the 10-year study period had a 25 percent reduced risk of glaucoma compared with people not taking the drug, researchers found.
"Glaucoma is a leading cause of blindness worldwide and classic open-angle glaucoma develops in late middle age or late age. So we hypothesized that a drug that mimics caloric restriction, such as metformin, might reduce the risk of glaucoma," said lead researcher Julia Richards, a professor of ophthalmology and visual sciences at the University of Michigan in Ann Arbor.
Exactly how metformin might reduce the risk of glaucoma isn't known, the researchers said. And, while this study found an association between metformin use and lower glaucoma risk, it wasn't designed to prove a cause-and-effect relationship.
Dr. Mark Fromer, an ophthalmologist at Lenox Hill Hospital in New York City, explained that glaucoma is caused by too much fluid in the eye, when fluid doesn't drain adequately, or when the blood vessels in the optic nerve are damaged. "Somehow metformin is affecting one of those conditions," he said.
Fromer pointed out that although the results of this study are impressive, using metformin to prevent or treat glaucoma in non-diabetic patients is problematic. Metformin could drop blood sugar too low in people without diabetes, he said.
"People without diabetes should not be taking metformin," he said. "If not monitored carefully by a doctor, it can have significant consequences," said Fromer, who was not involved with the study.
Richards, however, said that it might be possible to use metformin as a treatment for glaucoma even in people without diabetes.
"But since this study was done in a diabetic population, the conclusions are currently limited to this population," she said. "Further work, such as a clinical trial, would be needed to tell if this could be extended to non-diabetic populations or used to prevent progression of glaucoma in those who already have the disease," Richards said.
The study was published online May 28 in JAMA Ophthalmology.
For the study, Richards and colleagues collected 10 years of data on more than 150,000 people with diabetes. All were 40 or older at the start of the study. The investigators found that 4 percent of the participants developed glaucoma.
The researchers said that people taking the highest amount of metformin (more than 1,110 grams in two years) had a 25 percent reduced risk of developing glaucoma compared with those not taking the drug.
For every 1-gram increase in metformin taken, the risk was reduced by 0.16 percent. The researchers estimated that taking a standard dose of metformin (2 grams per day) for two years would reduce the risk for glaucoma by 21 percent.
This risk reduction was seen even after accounting for lower blood sugar levels, the study authors said. Other diabetes drugs were not associated with reduced risk of glaucoma, they added.