Drinking coffee protects against an eyelid spasm that can lead to blindness, a study suggests.
People who drank coffee had a lower risk of blepharospasm
Italian researchers looked at the coffee drinking and smoking habits of 166 people with blepharospasm.
Sufferers have uncontrollable twitching of the eyelid which, in extreme cases, stops them being able to see.
One or two cups of coffee a day seemed to reduce the risk of the condition, the team reported in the Journal of Neurology, Neurosurgery and Psychiatry.
Blepharospasm is a form of dystonia - a neurological movement disorder involving involuntary and sustained muscle contractions.
It usually affects people aged between 50 and 70 and someone with blepharospasm may be unable to prevent their eyes from clamping shut, so that, at times, they are effectively "blind".
The first symptoms may include eye irritation and discomfort, sensitivity to light and increased blinking.
Professor Giovanni Defazio and colleagues from the Department of Neurological and Psychiatric Sciences University of Bari in Italy said a previous study had suggested smoking had a protective effect on the condition.
They compared smoking and drinking habits in patients with the condition with patients with hemifacial spasm (a similar muscle spasm that usually begins in the eyelid muscles but then spreads to involve other muscles of the face) and people who were relatives of patients.
In the current study there was no significant association found with smoking but those who drank coffee were less likely to develop the condition.
The effect was proportional to the amount of coffee drunk and the age of onset of the spasm was also found to be greater in patients who drank more coffee - 1.7 years for each additional cup per day.
Professor Defazio said: "Our findings raise doubt about the association of smoking and blepharospasm but strongly suggest coffee as a protective factor.
"The most obvious candidate for the protective effect is caffeine, but the low frequency of decaffeinated coffee intake in Italy prevented us from examining the effects of caffeine on blepharospasm."
He suggested that caffeine may block receptors in the brain that are associated with the tremor and explained a similar mechanism had been proposed for the protective effects of caffeine in Parkinson's disease.
Professor David Wong, spokesman for the Royal College of Ophthalmologists, said the condition was fairly rare.
"Sometimes the condition is so bad that the patients spend most of the time with their eyes closed - they are effectively then visually impaired.
"Eye doctors treat patients mainly these days with Botulinum toxin."
Professor Kailash Bhatia, professor of clinical neurology at the UCL Institute of Neurology in London said although the condition seemed to be rare it could be under reported.
"This is an interesting finding, if you knew exactly how this worked it would help to develop treatments or preventive measures.
"It's something to look at in more detail."
Dr Tom Warner, medical adviser to the Dystonia Society, said a much larger study was needed to confirm the findings.
"Whilst the data is fascinating and offers new areas of research, it should not be accepted as a proven association and certainly does not mean we should be addressing our coffee intake."