The vision of thousands of people a year could be saved if a leading cause of blindness was detected in its early stages, say researchers.

Glaucoma occurs when the optic nerve is damaged and can be picked up during a routine eye examination.

It causes loss of peripheral (side) vision and eventually blindness. But many people are unaware they have it until it is too late.

Early detection and timely treatment would help to save the vision of thousands of people each year

Paul Sieving, National Eye Institute

In most cases, increased pressure inside the eye is a risk factor.

According to a study of 255 patients followed for six years, lowering pressure inside the eye can slow glaucoma damage and subsequent vision loss.

All had open-angle glaucoma, the most common form of the condition, which can be treated with medicines or lasers.

"These results strongly support the body of evidence suggesting that immediate treatment of early stage, open-angle glaucoma will slow the disease progression," said Paul Sieving, director of the US National Eye Institute, a co-sponsor of the US-Swedish study.

"Unfortunately, glaucoma has no early warning signs and many affected patients are unaware they have the disease until it has advanced.

"Once people have lost vision from glaucoma it cannot be regained. However, early detection and timely treatment would help to save the vision of thousands of people each year."

Eye exams

Open-angle glaucoma affects over four million people aged 40 and over, in the US alone.

It is caused by a number of different eye diseases which in most cases produce increased pressure within the eye.

Over time, it causes damage to the optic nerve. If picked up and treated early, vision can be preserved.

Ronald Pitts-Crick of the UK-based charity, the International Glaucoma Association, said the study emphasised the importance of regular eye examinations.

Advantage

"Early detection is the big thing," he told BBC News Online.

"Early treatment is essential if patients are going to retain sight to their best advantage."

The research is published in the latest issue of the journal Archives of Ophthalmology.

It was a collaborative effort between the University of Lund, Sweden, with centres in Malm�, Helsingborg, and Lund, Sweden, and Stony Brook University, Stony Brook, New York.