Glaucoma is caused by increased fluid pressure within the eye compressing the nerves at the back, which can lead to blindness if not treated.

The findings, published in the Journal of Epidemiology and Community Health, are based on 10,000 Japanese workers.

The authors and experts recommend more research, particularly because being short-sighted is a known glaucoma risk.

Eye strain

Dr Masayuki Tatemichi, from Toho University School of Medicine, and his colleagues tested the sight of workers in four different Japanese companies, employing over 5,000 people each.

The employees were asked to complete questionnaires about their computer use, both at home and at work, and any history of eye disease.

The researchers then divided the employees according to how much they used a computer, labelling them light, medium or heavy users.

Computer use was categorised in four blocks of five years, ranging from less than five years to more than 20 years, as well as four blocks of the average amount of time spent at the screen per session, ranging from less than one hour to more than eight hours at a time.

Those classified as heavy users tended to be men and younger.

Overall, 522 (5.1%) of the employees were found to have visual field abnormalities.

Workers who were classified as heavy computer users were more likely to be long-sighted (hypermetropia) or short-sighted (myopia).

Around a third (165) of these workers had suspected glaucoma.

Upon further analysis, heavy computer use, suspected glaucoma and short-sightedness appeared to be interlinked.

The authors do not know why this might be, but believe it could be that short-sighted people are more susceptible to computer use-related eye strain.

Glaucoma is the most important cause of irreversible blindness worldwide, affecting more than 500,000 people in the UK alone.

Compounded by the fact that more and more people are using computers, the researchers said: "In the next decade, therefore, it might be important for public health professionals to show more concern about myopia and visual field abnormalities in heavy computer users."

More research

But they said their findings needed confirming because the study included mainly men and the refractive errors (which indicate how short- or long-sighted someone is) were not measured officially.

Nick Astbury, president of the Royal College of Ophthalmologists, pointed out that Japanese populations have a high prevalence of myopia anyway and that short-sightedness is a known risk factor for glaucoma.

"I doubt whether staring at computers makes any difference," he said.

David Wright, chief executive of the International Glaucoma Association, said: "There may be a risk in heavy use of computer equipment.

"It would be wise for anyone involved in such heavy usage to ensure that they receive regular comprehensive eye examinations in order to detect the earliest possible signs of the development of glaucoma when treatment is most effective."

He said three eye tests should be carried out to check for glaucoma: ophthalmoscopy (a visual examination of the optic disc), tonometry (a measurement of pressure in the eye) and perimetry (which checks for visual field anomalies).

"It will be important to follow this study with further research in other ethnic populations in order to establish the complete validity of this initial indication of a potential problem and also to address the ethnic risk factors should the evidence add to the Japanese report," he said.