Kids seem to spend endless hours on smartphones, computers and tablets these days. The best thing parents can do to prevent it is to encourage youngsters to spend more time outdoors in the sunlight.

    There has been a massive rise around the globe in short-sightedness—or myopia as it's officially known—over recent decades. Myopia or short-sightedness is becoming more common. Lack of natural light seems to be the key issue. “The main factor seems to be a lack of exposure to direct sunlight, because children who study a lot and who use computers or smartphones or tablet computers a lot have less opportunity to run around outside and are less exposed to sunshine and because ofthatchildren seem to be at more risk of developing shortsightedness.”

    Professor Hammond says, “It may be there's no coincidence that in East Asian countries, the most myopic ones all relate may to be the that maths league tables(排名表). These kids are being pushed with very intensive education from a very young age and spend a lot of time indoors studying close up. Therefore the concern is that all close work—like playing with the iPhone—carries the potential that it could make them more shortsighted.”

    The best thing to do, say the experts, is to get children playing outside as much as possible. “In a perfect world, probably on average across the week and the weekend, two hours a day outdoors is protective of becoming short-sighted in children. Healthy diet is really also important—in terms of getting oily fish, green vegetables, green leafy vegetables as much as possible.

    “What we need to look at is ways of modifying the impact that these activities have on their visual development.” Professor Hammond said, “There are eye drops and other treatments to slow myopia progression. But in terms of preventing myopia itself, there isn't any data out there at the moment in terms of the question, 'Could the drops we use slow progression or stop myopia developing at all? ' ”