Drinking a cup of tea a day could prevent a leading cause of blindness, a study has discovered.

Researchers at the University of California Los Angeles found tea-drinkers were 74% less likely to suffer glaucoma.In Britain, about 2% of the population over 40 have the condition – which leads to a million NHS visits per year.

The study asked 1,678 participants how often and how much they had drunk of caffeinated and decaffeinated drinks, including soft drinks and iced tea.

Professor Dr Anne Coleman said: “Individuals who consumed hot tea daily had reduced odds of having a diagnosis of glaucoma. Interestingly, this association was not observed with the consumption of iced tea or decaffeinated hot tea.”

She said tea has flavonoids associated with the prevention of cancer, cardiovascular disease and diabetes.

But other experts criticised the study. Dr Graham Wheeler, of University College London, said: “The authors did not explore how biologically this association might work, which means the results say nothing about one thing causing another.”