FRIDAY, May 2 (HealthDay News) -- While diabetes has long been associated with the potentially sight-stealing disease diabetic retinopathy, it appears that another serious eye disease -- glaucoma -- may also be a complication of the metabolic disorder.

A recent study in the journal Ophthalmology found that women with diabetes have about a 70 percent increased risk of developing the most common form of glaucoma -- primary open-angle glaucoma -- compared to women without diabetes.

"The study supports the notion that type 2 diabetes is associated with an increased risk of glaucoma," study lead author Dr. Louis Pasquale, co-director of the glaucoma service at the Massachusetts Eye and Ear Infirmary and an assistant professor of ophthalmology at Harvard Medical School, said in a prepared statement.

Primary open-angle glaucoma affects an estimated 2 million Americans, according to the U.S. National Eye Institute, and it is one of the leading causes of blindness.

Yet the link between diabetes and glaucoma hasn't been proven conclusively.

"There are a number of things, like diabetes, that appear to be a risk factor in a lot of population studies, but the association between diabetes and glaucoma is somewhat controversial," explained Dr. Joel Schuman, chairman of the department of ophthalmology at the University of Pittsburgh School of Medicine and Medical Center, and the director of the UPMC Eye Center.

Another study, also published in Ophthalmology, failed to find a link between diabetes and glaucoma in a trial that included almost 4,000 people from the Netherlands.

But, Pasquale's study was significantly larger, including more than 76,000 women enrolled in the 20-year-long Nurses' Health Study. And, the available evidence is convincing enough for the American Diabetes Association to conclude that the risk of glaucoma is increased in people with diabetes.

Glaucoma occurs when there's a gradual increase in the normal fluid pressure inside the eyes. This causes damage to the optic nerve, resulting in vision loss and blindness. Early detection and treatment can help prevent serious vision loss. About 50 million Americans are at risk for vision loss from glaucoma.

Schuman said there are a number of ways that diabetes could increase the risk of glaucoma. One way is by causing elevation in pressure within the eye. Or it's possible, he said, that diabetes could increase the susceptibility of the optic nerve to damage.

He said there's also one form of glaucoma that's known to be directly related to diabetes -- neovascular glaucoma. In this type of glaucoma, there's a reduction of oxygen supply to the retina, which causes the retina to send out signals for more oxygen and for new blood vessels to form. When these new blood vessels form, they cause scarring and block the normal drainage system in the eye, causing pressure to build up in the eye.

The most important thing someone with diabetes can do to protect their eyes is to get regular eye exams, Schuman said. Glaucoma generally has no early symptoms.

"There's no way to detect glaucoma without an exam, and the only way to prevent the loss of vision from glaucoma is to treat the disease early. You can't get back nerve damage that's been lost," he said.

Diabetes specialist Dr. David Oyer, of Northwestern Memorial Hospital in Chicago, said he recommends that people with diabetes have their eyes checked once a year by an ophthalmologist for glaucoma and other serious eye diseases associated with diabetes.

"The most important thing for reducing your risk of complications is to keep your blood sugar down both pre- and post-meal," Oyer said. He also recommends getting your A1C level checked every three to six months and keeping that number below seven, preferably below 6.5. A test of A1C (also known as glycated hemoglobin, or HbA1c) provides a snapshot of your average blood glucose control for the past two to three months, according to the American Diabetes Association.

Schuman also said regular exercise might help. "Exercise is good for the eye, just as it is for the rest of the body. Regular, vigorous exercise does lower eye pressure and probably affects circulation to the eye," he said.

More information

To learn more about glaucoma, visit the National Eye Institute.

SOURCES: Joel Schuman, M.D., Eye and Ear Foundation professor and chair, department of ophthalmology, University of Pittsburgh School of Medicine and Medical Center, and director of UPMC Eye Center; David Oyer, M.D., endocrinologist, Northwestern Memorial Hospital, Chicago; Ophthalmology

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