People who drink coffee are less likely to develop an involuntary eye spasm called primary late onset blepharospasm, which makes them blink uncontrollably and can leave them effectively ‘blind’, according to a study published online ahead of print in the Journal of Neurology Neurosurgery and Psychiatry.

Late onset blepharospasm is a dystonia in which the eyelid muscles contract uncontrollably; this starts as involuntary blinking but in extreme cases sufferers are rendered functionally blind despite normal vision because they are unable to prevent their eyes from clamping shut.

They suggest that caffeine blocks adenosine receptors as has been proposed for its mechanism in protecting against Parkinson’s disease.

The authors estimate that people need to drink one to two cups of coffee per day for the protective effect to be seen.