People with a thyroid disorder run an increased risk of developing the eye disease glaucoma, a new study suggests.
In fact, those with glaucoma are 38 percent more likely to have had a thyroid condition at some point in their life, said the study authors, from the University of Alabama at Birmingham. Glaucoma is the leading cause of irreversible blindness worldwide.
"Studies like this are very useful in understanding what causes this disease," said lead researcher Gerald McGwin, vice chairman of the Department of Ophthalmology at the university's School of Medicine.
"If we can determine that thyroid problems are related to glaucoma, then we can make some hypotheses about what the mechanism behind that relationship might be and help us understand what might be the cause of glaucoma," McGwin said. "And that may lead to more effective treatments or preventive measures."
The findings were published online Oct. 16 in the British Journal of Ophthalmology.
For the study, McGwin's team collected data on 12,376 people who participated in the 2002 National Health Interview Survey. They were asked if they'd ever been diagnosed with a thyroid problem or glaucoma. Slightly more than 4.5 percent said they had glaucoma, and 12 percent said they had been diagnosed with a thyroid problem.
Among people who had glaucoma, 6.5 percent said they had a thyroid problem, while 4.4 percent said they'd never had a thyroid condition.
People with thyroid problems should see an ophthalmologist or make their ophthalmologist aware of their thyroid condition, McGwin advised. "Somebody who has a history of thyroid problems and has not seen an ophthalmologist may have a heightened level of concern about their eyesight," he said.
The thyroid produces hormones essential for the functioning of every cell in the body; these hormones help regulate growth and chemical reactions.
In glaucoma, the optic nerve becomes progressively damaged and, if not treated, leads to loss of vision and even blindness.
The study authors suggested that the link between glaucoma and thyroid disorders may owe to chemical deposits in the blood vessels that circulate blood to the eye, causing an increase in pressure within the eyeball. Increased pressure in the eyeball is the main feature of glaucoma.
Dr. Andrew Iwach, a spokesman for the American Academy of Ophthalmology and executive director of the Glaucoma Center of San Francisco, said the potential link between thyroid problems and glaucoma is interesting and should be taken into account, but it still needs to be proven. The best advice is to get your eyes checked, he said.
"If you haven't seen an ophthalmologist by age 40, that's a great time to get a baseline exam," Iwach said.
"People may not know they are at risk for glaucoma. You are functioning fine, and yet slowly, this disease can chip away at the optic nerve, and by the time you have symptoms from glaucoma, oftentimes there's not really much we can do," he said.
In a related study, researchers at Rush University Medical Center in Chicago found that many elderly people have undiagnosed thyroid problems, including thyroid cancer. Older patients are twice as likely to be diagnosed with thyroid cancer as younger patients. Thyroid cancer was found in 41 percent of patients over 65, compared with 22 percent among younger patients, the researchers found.
Most thyroid cancer is treatable, and age should not be a barrier to treatment, noted the researchers, who were expected to present their findings Oct. 15 at the 2008 Clinical Congress of the American College of Surgeons, in San Francisco.
More information
For more on thyroid diseases, visit the U.S. National Library of Medicine.
SOURCES: Gerald McGwin, Ph.D., vice chairman, Department of Ophthalmology, University of Alabama at Birmingham School of Medicine; Andrew Iwach, M.D., spokesman, American Academy of Ophthalmology, and executive director, Glaucoma Center of San Francisco; Oct. 16, 2008, British Journal of Ophthalmology, online