Glaucoma is the buildup of fluid pressure in the eye. Over time, this increase in intraocular pressure (IOP) damages the optic nerve and results in a diminished field of vision and may eventually lead to blindness.

There seems to be a simple way to protect against glaucoma, however. Drinking hot, caffeinated tea significantly reduces the risk of developing glaucoma, a study has found.

Drinking decaffeinated, hot tea had no effect on glaucoma risk; neither did coffee, iced tea, or soft drinks.

The findings run counter to several earlier studies suggesting that drinking coffee was associated with developing glaucoma, Anne Coleman, one of the researchers, told TheDoctor. One of those studies had found that drinking more than five cups of coffee per day increases the risk of a certain type of glaucoma. Coleman and her team wanted to look beyond coffee, and consider other caffeinated beverages, since caffeine appeared to be what increased IOP.

From the responses of almost 1,700 participants in the National Health and Nutrition Examination Survey (NHANES) in 2005-2006, the year survey participants received eye exams, researchers found five percent of the participants had glaucoma.

People in the study who drank at least one cup of hot, caffeinated tea per day had a 74 percent decreased risk of developing glaucoma, compared to those who did not drink hot, caffeinated tea. Drinking decaffeinated, hot tea had no effect on glaucoma risk; neither did coffee, iced tea, or soft drinks.

“It was kind of surprising that it was hot, caffeinated tea,” said Coleman, but the polyphenol content of coffee and tea are different, with caffeinated tea delivering a different profile of polyphenols with more flavonoids than in coffee.

The polyphenols in hot, caffeinated tea may be interacting with the physiology of the optic nerve, said Coleman, the Fran and Ray Stark Professor of Ophthalmology at the UCLA David Geffen School of Medicine and a professor of epidemiology at the UCLA School of Public Health. Polyphenols have been shown to have neuroprotective effects in animals, she said, but it is not yet known if they have this effect in humans.

All the different recommendations about caffeine and glaucoma can be confusing.“If you are a tea drinker, I’d keep on drinking tea,” Coleman said, adding, “But I wouldn’t specifically drink tea just to prevent glaucoma, because we haven’t done enough research to recommend that yet.”

And should coffee drinkers stop? Probably not. “I’d continue to drink coffee, because it has been shown to have positive effects for other conditions, such as Parkinson’s disease,” said Coleman.

For those worried about glaucoma, it certainly won't do any harm to have a cup of tea every so often.

The study is published in the British Journal of Ophthalmology.