The strong emphasis on educational achievement in China, Japan and other parts of South East-Asia may be coming at a heavy price. Researchers say that hard work at school plus the lack of exposure to outdoor light is damaging the eyes of almost nine out of ten students - with one in five at serious risk of visual impairment and blindness.

The scientists say that young people need up to three hours a day of outdoor light, but many infants are also missing out as they nap during lunch time. Dr. Ian Morgan is the lead author of the study:

I think what's happened in South-East Asia is we've got a double whammy. We've got the massive educational pressures and we've got the construction of a child's day in a way that really minimises the amount of time they spend outside in bright light.

The scientists say that genetic factors, long thought to play a big role in short-sightedness, are not as important as the environment. They point to Singapore as a place with several distinct ethnic groups, all of whom are now suffering high levels of myopia.

The authors suggest that mandatory time outdoors should be considered by educational authorities across South-East Asia as a way of dealing with the problem.