Women who use oral contraceptives for several years or longer may want to consider having their eyes checked more regularly as they get older. New research suggests that the pills may double their lifetime risk of developing glaucoma, a degenerative eye disease that can cause blindness if left untreated.
The researchers cautioned that their findings should not discourage women from using oral contraceptives, since the risk of glaucoma for the average adult over the age of 40 remains fairly low. But they said that doctors should be aware of the link, and that women who are using birth control pills — an estimated 11 million or more American women — should keep tabs on their long-term eye health.
Why birth control pills might play a role in glaucoma is not entirely clear. But cells in the optic nerve contain estrogen receptors that are believed to play a role in protecting the eyes from age-related decline, and the pills may interfere in that process by depressing estrogen levels. Researchers have previously found that women who enter menopause early or take medications that block estrogen, like drugs used against breast cancer, also have an elevated risk of glaucoma.
A sometimes painful eye disease, glaucoma affects between two and three million Americans. The most prevalent form of the condition, called open angle glaucoma, is caused by the gradual clogging of drainage canals in the eyes, creating a build-up of pressure inside the eye. The disease is more common in African Americans and in people who have a family history of the illness.
The new study looked at data on 3,406 women over the age of 40 who were followed for many years as part of the ongoing National Health and Nutrition Examination Survey, which is carried out by the Centers for Disease Control and Prevention. The women regularly underwent eye exams and answered questions about their reproductive health and medical histories.
Women who reported having used birth control pills of any kind for three years or longer had a 5 percent risk of developing glaucoma, compared with a risk of about 2.5 percent in the general population, said Dr. Shan Lin, a professor of clinical ophthalmology and the director of the glaucoma service at the University of California, San Francisco medical school. Dr. Lin presented his findings this week at a meeting of the American Academy of Ophthalmology in New Orleans.
Dr. Lin cautioned that the findings were preliminary and showed only a correlation, not causation. But together with data from previous studies they suggest that there is a relationship between estrogen levels and the development of eye disease.
Two years ago, a large study published in the journal Eye looked at data on nearly 80,000 women who were followed for three decades as part of the Nurses' Health Study. Women who reported using birth control pills at any point in their lives did not have an elevated risk of glaucoma. But those who specifically had used them for five years or longer did experience a modestly elevated risk of the disease.
A growing body of evidence suggests that women who go into menopause early or have their ovaries removed are also at slightly greater risk of glaucoma, while those who experience menopause later and take postmenopausal hormones appear to be at lower risk, said Dr. Louis Pasquale, the author of that study and an associate professor of ophthalmology at Harvard Medical School. He said that estrogen appears to have a "maintenance effect" on retinal ganglion cells in the eye, which are known to have estrogen receptors.
"We think the presence of estrogen helps keep those cells alive," Dr. Pasquale said. "And so things that happen to women over the course of their lifetime that would reduce their estrogen would increase their risk because glaucoma is a degenerative condition."
In men, the same cells of the eye appear to have estrogen receptors as well. But Dr. Pasquale said it is not yet known whether fluctuations in hormone levels would have a similar effect in men. "We're just beginning to scratch the surface of that," he said.
Dr. Pasquale said that researchers were working on developing topical agents for the eyes that could mimic the protective effect of estrogen. Those drugs, however, have only been tested in animal models, and they are perhaps 10 to 15 years away from human trials.
Ophthalmologists generally recommend annual eye screenings for people 65 and older. But African Americans and people who have diabetes or a family history of eye diseases are typically told to begin the screenings sooner, and women with a history of taking birth control for long periods may be advised to start earlier as well.
"I think, over all, that women need to be cognizant that there may be a connection between their reproductive health and their eyes," said Dr. Pasquale. "While one wouldn't necessarily make decisions about their reproductive health based on what might happen to their eyes, they should have their eyes examined if they're someone that took a lot of oral contraceptives or if they have menopause early."
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