According to an American research, drinking more than three cups of coffee a day may increase the risk of vision loss and blindness.
Even moderate amounts of the drink make developing the devastating eye condition glaucoma more likely.
The study, published in the journal Investigative Ophthalmology & Visual Science, suggests coffee lovers reduce their intake to reduce their chances of developing the condition.
Glaucoma occurs when the drainage tubes within the eye become slightly blocked.
This prevents eye fluid from draining properly, causing pressure to build up.
When the fluid cannot drain properly, pressure builds up.
This can damage the optic nerve, which connects the eye to the brain, and the nerve fibres from the retina (the light-sensitive nerve tissue that lines the back of the eye).
The researchers, from the Brigham and Women’s Hospital in Boston, suggest that compounds found in coffee may increase pressure within the eyeball, causing a vision-destroying condition known as exfoliation glaucoma.
This occurs when material is rubbed off both the eye’s iris and lens, which then clogs up the eyeball’s fluid-draining system, leading to increased pressure within the eye
However, no correlation was with other caffeine products such as tea, cola or chocolate.
Previous research has found that Scandinavian populations have the highest occurrence of exfoliation glaucoma.
They also have the highest consumption of caffeinated coffee in the world.
The new study assessed more than 120,000 people in the UK and U.S. who were over 40 and not suffering from glaucoma.
They completed questionnaires about how much coffee they drank and their medical records were checked for a history of glaucoma.
Those who drank more than three cups a day were had an increased risk of developing glaucoma compared with those who abstained.
Women with a family history of glaucoma also had an elevated risk.
Coffee may not be without its benefits, however. Research published earlier this year in the New England Journal of Medicine found drinking four to five cups a day possibly reduced the risk of heart disease, stroke and diabetes, among other conditions.
GLAUCOMA: THE DISEASE THAT DESTROYS VISION
Glaucoma affects 1% of people over 40 and around 5% of people over 65.
Those at increased risk include diabetics, people of African or black Caribbean origin and those with a family history of glaucoma.
The condition develops very slowly and, as a result, usually has no noticeable symptoms.
Sight loss also goes unnoticed because the first part of the eye to be affected is the outer field of vision (peripheral vision).
The damage then slowly works inward, towards the centre of the eye.