Time Outdoors and Healthy Eyes
In a matter of just two generations myopia or shortsightedness has risen from 20 to almost 90 percent in East Asian city dwelling children. And it turns out that in most cases it’s not a genetic disorder but rather an environmental factor.
Children who live in cities in China, Taiwan, Hong Kong, Japan, Singapore and South Korea are faced with massive educational pressures. In addition, many East Asian cultures promote staying inside during lunchtime and having a nap.
When East Asian children aren’t in school they are inside watching television, playing video games or reading. On average East Asian children are spending only 30 minutes each day outside exposed to sunshine or filtered light from an overcast sky.
According to Professor Ian Morgan of the Australian National University the reason for the dramatic rise in shortsightedness amongst East Asian city dwelling children is due to a lack of exposure to sunshine.
Exposure to sunshine stimulates the body’s production of a chemical called dopamine, which is known to prevent the eyeball from elongating and in turn distorting the focus of light entering the eye.
Australian children spend up to three hours a day outside and shortsightedness amongst their youth is about 10 percent. The rate amongst children in Britain and the U.S. is higher at about 35 percent whilst in Africa it’s only about 3 percent.
This recent study highlights the importance of children getting outside to help maintain healthy eyes. Getting children to play outside and involved in physical activity helps protect them against the onset of type II diabetes and obesity, vitamin D deficiency and osteoporosis.
Snubbing the outdoors for books, video games and TV is the reason up to nine in ten school-leavers in big East Asian cities are near-sighted, according to a study.
Neither genes nor the increase in activities like reading and writing is to blame, the researchers suggest, but a simple lack of sunlight.
Exposure to the Sun’s rays is believed to stimulate production of the chemical dopamine, which in turn stops the eyeball from growing elongated and distorting the focus of light entering the eye.
“It’s pretty clear that it is bright light stimulating dopamine release which prevents myopia,” says researcher Ian Morgan of the Australian National University, lead author of the study published in The Lancet medical journal.
The average primary school pupil in Singapore, where up to nine in ten young adults are myopic, spent only about 30 minutes outdoors every day – compared to three hours for children in Australia where the myopia prevalence among children of European origin is about 10 per cent.
The figure in Britain was about 30 to 40 per cent and in Africa “virtually none” – in the range of two to three per cent, according to Morgan.
More than other groups, children in East Asia “basically go to school, they don’t go outside at school, they go home and they stay inside. They study and they watch television,” says Morgan.
The most myopic school-leavers in the world are to be found in cities in China, Taiwan, Hong Kong, Japan, Singapore and South Korea, where between 80 and 90 per cent were affected. Of these, 10 to 20 per cent had a condition called high myopia, which can lead to blindness.
“Most of what we’ve seen in East Asia is due to the environment, it is not genetic,” says Morgan, contrary to the common belief 50 years ago.
The researchers, collating the findings of studies from around the world, stressed that being a bookworm or computer geek does not in itself put you at risk. “As long as they get outside it doesn’t seem to matter how much study they do,” explained Morgan.
“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.”
Morgan says children who spent two to three hours outside every day were “probably reasonably safe”. This could include time spent on the playground and walking to and from school.
“The amount of time they spend on computer games, watching television can be a contributing factor. As far as we can tell it is not harmful in itself, but if it is a substitute for getting outside, then it is,” he says.
Morgan says ways must be found to get children to spend more time in reasonably bright daylight without compromising their schooling.
“It is going to require some sort of structural change in the way a child’s time is organized in East Asia because there is so much commitment to schooling and there is also a habit of taking a nap at lunchtime, which is from our perspective prime myopia prevention time.”
Researchers say students working very hard in school and missing out on outdoor light are causing the “extraordinary rise” in the problem. The scientists told the Lancet that up to one in five of these students could experience severe visual impairment and even blindness.
Prof Ian Morgan
Australian National University
“They’ve gone from something like 20% myopia in the population to well over 80%, heading for 90% in young adults, and as they get adult it will just spread through the population. It certainly poses a major health problem.” Eye experts say that you are myopic if your vision is blurred beyond 2m (6.6ft). An elongation of the eyeball that happens when people are young often causes it.
According to the research, the problem is being caused by a combination of factors – a commitment to education and lack of outdoor light.
The scientists believe that a chemical called dopamine could be playing a significant part. Exposure to light increases the levels of dopamine in the eye and this seems to prevent elongation of the eyeball.
“We’re talking about the need for two to three hours a day of outdoor light – it doesn’t have to be massively sunny, we think the operating range is 10-20,000 lux, we’re not sure about that – but that’s perfectly achievable on a cloudy day in the UK.
“Whether it’s a purely environmental effect or an environmental effect playing a sensitive genome, it really doesn’t matter, the thing that’s changed is not the gene pool – it’s the environment.” The time children spend outdoors could be linked to a reduced risk of being shortsighted, research suggests.
An analysis of eight previous studies by University of Cambridge researchers found that for each additional hour spent outside per week, the risk of myopia reduced by 2%. Exposure to natural light and time spent looking at distant objects could be key factors, they said. The studies involved more than 10,000 children and adolescents.
Dr Justin Sherwin and his research team concluded that shortsighted children spent on average 3.7 fewer hours per week outdoors than those who either had normal vision or were long-sighted. “On the other hand, increasing outdoor physical activity could protect against diabetes and obesity, vitamin D deficiency and osteoporosis, for example,” he said.
Shortsightedness is a common eye condition that causes distant objects to appear blurred, while close objects can be seen clearly. Myopia is the medical term for shortsightedness. It is much more common today in the UK and the United States than it was just 30 to 40 years ago. Approximately 1-2% of five- to seven-year-olds in the UK have myopia.
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