Students in military uniforms balance bottles of water on their heads as they practice goose-stepping marching during a military training session at a college in Zhengzhou, Henan province in China. Over 90 percent of youth in China are myopic. REUTERS

Children need to be exposed to an hour or more of outdoor light daily to prevent short sightedness from developing. The research at Queensland University of Technology was looking for solutions to address the myopia epidemic in children.

While computer and smart phone screens and long hours of study have been suspected to alter growth of the eyeball and cause myopia, the evidence has not been satisfactory. Increasingly, the spotlight has been on outdoor light for quite some time now. Turns out natural light is protective for the eye.

Optometrist and lead researcher on the project, Associate Professor Scott Read who is the director of research at QUT's School of Optometry and Vision Science, said children need to spend more than an hour and preferably at least two hours a day outside to help prevent myopia from developing and progressing.

The QUT study measured children's eye growth using wristwatch light sensors to record light exposure and physical activity for a fortnight during both warmer and colder months. "Children exposed to the least outdoor light had faster eye growth and hence faster myopia progression," Professor Read said.

Kathryn Rose, head of orthoptics at the University of Technology, Sydney, also has showed similar results last year after studying more than 4,000 children at Sydney primary and secondary schools for three years.

Myopia now affects around half of young adults in the United States and Europe while 90 percent of Chinese youth are short-sighted.

Speaking at the Australian Vision Convention in Queensland on the weekend, Professor Read said: "Optometrists need to make their patients aware that less than 60 minutes' exposure to light outdoors per day is a risk factor for myopia. It looks like even for those with myopia already, increasing time outside is likely to reduce progression."

A global study, published by the Brien Holden Vision Institute, in February forecast that 10 per cent of the world's population will be at risk of blindness by 2050 if steps are not taken to stop myopia turning into high myopia (requiring glasses with a prescription of minus five or stronger). Half the population will suffer from myopia.

While it is still not fully understood how light protects the eye, the favoured theory relates to stimulation of dopamine in the retina by light. The neurotransmitter blocks the elongation of the eye during development years. Under dim light as in indoors, the retinal dopamine cycle of release during the day is disrupted and eye growth leads to myopia.

In regions where children spend 3 to 4 hours outdoors, myopia is significantly low.