Glaucoma produces fluid pressure to pile up inside the eye (intraocular pressure), affecting the optic nerve.
The study also has many limitations, like the small number of participants with glaucoma, lack of data on when glaucoma had been diagnosed, and lack of data on a few potentially influential factors such as cup size, tea type, or the length of brewing time. Researchers have found that drinking a cup of hot tea at least once a day may lower the risk of developing glaucoma, one of the leading causes of blindness worldwide. Glaucoma affects 57.5 million people around the world now, and is expected to increase to 65.5 million by 2020.
The study, published online in the British Journal of Ophthalmology, found that compared with those who did not drink hot tea every day, those who did, had a lower glaucoma risk.
Researchers who wrote in the British Journal of Opthalmology in the USA reported how they examined information from a 2005-2006 nationwide health and nutrition survey, observing the results of eye examinations from 1,678 participants aged 40 and above.
The survey used a range of tools, including interviews, physical examinations, and blood samples, aiming to give a detailed pictured of health in the United States population.
But coffee, iced tea and soft drinks don't seem to make any difference, the researchers found.
The team chose the 2005-2006 survey because it also gathered data on glaucoma diagnoses.
Out of the 84 participants who were found to have glaucoma, there appeared to be no link between drinking coffee, soft drinks or iced tea and them having the condition.
This could help explain why coffee did not have the same effect on glaucoma risk, according to Anne Coleman, the lead researcher of the study and director of the UCLA Mobile Eye Clinic.
Participants were asked how often and how much they had drunk of caffeinated and decaffeinated drinks, including soft drinks and iced tea in the preceding year.
Those benefits may include a reduced risk of chronic diseases like heart disease, diabetes and cancer.
Individuals who consume hot tea daily may have a lower risk of developing glaucoma, according to a study published online December 14 in the British Journal of Ophthalmology.
"Further research is needed to establish the importance of these findings and whether hot tea consumption may play a role in the prevention of glaucoma", said the researchers.