The Medicine Cabinet-Ask the Harvard Experts: Metformin may lower risk of glaucoma in people with diabetes

The Medicine Cabinet-Ask the Harvard Experts: Metformin may lower risk of glaucoma in people with diabetes

Tribune Content Agency — June 2, 2015

By Howard LeWine, M.D., Tribune Content Agency

Q: I just read that the drug metformin might help prevent glaucoma. I have pre-diabetes and am working on lowering my blood sugar. My last eye exam indicated my eye pressures were in the high normal range. Should I start metformin now?

A: Metformin is the best medicine to use first for people with type 2 diabetes. And some experts suggest people with pre-diabetes should consider taking it, in addition to diet and exercise.

You have a higher than average risk of developing open-angle glaucoma, so your question is very timely. A study published last week in the journal JAMA Ophthalmology suggested metformin might decrease the risk of glaucoma in people with diabetes.

Glaucoma is a group of eye diseases that can lead to irreversible vision loss through damage to the optic nerve, a collection of specialized nerve fibers that connect the back of the eye (the retina) to the brain.

Glaucoma is caused by a problem with the circulation of fluid in the eye. Normally, a clear liquid called aqueous humor circulates continuously inside the front part of the eye. To keep a healthy pressure within the eye, an equal amount of this fluid flows out of the eye.

In open-angle glaucoma, this drainage system becomes less efficient. The outflow of fluid slows. The fluid then backs up in the eye, like water in a clogged sink. Internal pressure in the eye rises.

This, in turn, puts stress on the optic nerve. If the pressure continues, nerve fibers that carry the vision messages to the brain begin to die. Vision starts to fade. If left untreated, glaucoma can lead to blindness.

Results of this study showed a 25 percent lower risk of open-angle glaucoma in people who took the highest amount of metformin compared with those who didn’t take the drug. The higher the dose of metformin, the lower the risk of open-angle glaucoma. Even people taking smaller doses of metformin had a lower risk compared with non-users. Other diabetes drugs did not have the same effect.

Talk with your doctor. I think it’s very reasonable to start a low dose of metformin now. But diet and exercise should remain your primary therapy to prevent diabetes. And calorie restriction might also lower your glaucoma risk.

(Howard LeWine, M.D., is a practicing internist at Brigham and Women’s Hospital, Boston, Mass., and Chief Medical Editor of Internet Publishing at Harvard Health Publications, Harvard Medical School.)

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