Life is a blur according to a population-based study published on Monday showing that rates of myopia which means difficulty seeing distant objects are soaring. This has made doctors wonder what could be causing the decline in human vision.

Some suspect both an increase in our close-up work time in front of computer and in the decrease in time spent outdoors.

Researchers at the National Eye Institute, part of the National Institutes of Health, found that rates of myopia in people aged 12 to 54 increased from 25 per cent in 1971-72 to 41.6 per cent in 1999-2004. The study included people with a range of myopia, from mild to severe.

"It's very interesting," lead author Susan Vitale, a research epidemiologist with the National Eye Institute said.

"All of the evaluations show a major shift in myopia rates and the reason is not clear," said Dr David S. Friedman, a professor of ophthalmology and international health at the Wilmer Eye Institute, Johns Hopkins Medical Center.

Children today grow up in front of computers rather than on baseball fields and instead of running behind the ball hit from afar or seeking each other out in sprawling city parks, they are following the movements of a cursor. Such early activities, Vitale said, shape visual acuity.

Although myopia can be treated with glasses or contacts, it increases the risk of other eye diseases, such as glaucoma, retinal detachment and blindness.