Which part of the world has the most nearsighted（近视的）students？Just look around you----it's East Asia．Nine in 10school leavers in major East Asian cities are nearsighted，according to the BBC．Experts say books and video games are not to blame．East Asian students，they say，aren't getting enough sunlight．
People become nearsighted because their eyeballs grow out of shape and light entering their eyes cannot focus（聚焦） correctly．The body can produce a chemical called dopamine （多巴胺） to stop eyeballs from changing shape．Sunlight can help our bodies produce more dopamine，reported AFP．
According to the study，primary school students in Singapore spend only 30minutes outdoors every day； in Australia，kids spend about three hours a day outside．As a result，fewer children in Australia are nearsighted----only 10percent，compared with 90percent in Singapore．
"Children in East Asia usually go to school…go home and stay inside．They study and they watch television，"Ian Morgan of the Australian National University told AFP．
But being a bookworm or a couch potato does not directly harm the eyes，added Morgan．"As long as they get outside，it doesn't seem to matter how much study they do，"he explained．"There are some kids who study hard and get outside and play hard and they are generally fine．The ones who are at major risk are the ones who study hard and don't get outside．"
Scientists used to believe that people from Asian countries were genetically（由基因决定的）more likely to become nearsighted．However，when they found the proportion （比例） of nearsighted people in these countries had increased from 30to 90percent in the past few decades（十年），they realized they were wrong．
"Any type of simple genetic explanation just doesn't fit with that speed of change； gene pools just don't change in two generations，"said Morgan．What has changed is the time children spend outdoors．As a result of massive （巨大的） education