Scientists blame surging Asian myopia rates on indoor lifestyle
Researchers say they have found that surging Asian rates of shortsightedness may be curbed if children are encouraged to go outdoors more
Myopia isn't an infectious disease, but it has reached nearly epidemic proportions in parts of Asia.
In Taiwan, for example, the percentage of seven-year-old children suffering from nearsightedness rose from 5.8 per cent in 1983 to 21 per cent in 2000. An incredible 81 per cent of Taiwanese 15-year-olds are myopic.
The prevalence of high myopia, an extreme form of the disorder, has more than doubled in Asia since the 1980, and children who suffer myopia early in life are more likely to progress to high myopia. High myopia is a risk factor for such serious problems as retinal detachment, glaucoma, early onset cataracts and blindness.
The explosion of myopia is a serious public health concern and doctors have struggled to identify the source of the problem. A variety of risk factors has been linked to the disorder: Frequent reading, participation in sports, television watching, protein intake and depression. When each risk factor was isolated, however, its overall effect on myopia rates seemed to be fairly minimal.
But researchers believe they are now closing in on a primary culprit: Too much time indoors.
In 2008 orthoptics professor Kathryn Rose found that only 3.3 per cent of six and seven-year-olds of Chinese descent living in Sydney, Australia, suffered myopia, compared with 29.1 per cent of those living in Singapore. The usual suspects, reading and time in front of an electronic screen, could not account for the discrepancy.
The Australian cohort read a few more books and spent slightly more time in front of the computer, but the Singaporean children watched a little more television. On the whole, the differences were small and probably cancelled each other out. The most glaring difference between the groups was that the Australian children spent 13.75 hours per week outdoors compared with 3.05 hours for children in Singapore.
Rose, whose research was covered in the magazine Science News, pointed out the vastly different educational cultures that prevailed in Sydney and Singapore. Most Australian children participate in one year of part-time preschool, which teaches social skills and communal play more than reading or writing, followed by one year of kindergarten.
During the same stage of development, the typical Singaporean child goes through three largely full-time years of education in an attempt to ensure that he or she can read before beginning school. Full-time schooling likely comes at the expense of time spent playing outside.
There isn't yet broad agreement on why the outdoors might protect children from nearsightedness. One hypothesis is that children focus their gaze on more distant objects in the outdoors, while indoor time is usually spent staring at a computer screen, book or toy only a couple of feet away. Studies on rhesus monkeys, however, suggest that simple light exposure is the more likely explanation.
While myopia is extremely uncommon among non-human primates, researchers can easily induce myopia by depriving infant monkeys of normal outdoor lighting levels.
This is, on the whole, an encouraging finding. If children became myopic due to looking at objects too closely, then this would pose an unsolvable dilemma: Choosing between teaching children to read and protecting their eyesight.
If the problem is just a matter of light intensity, however, parents could send children outside to read or purchase high- intensity light sources that mimic outdoor exposure.
According to a 2004 study from the University of Michigan, the average US child in 2002 spent exactly half as much time participating in outdoor activities as did children in 1981.
While myopia hasn't yet reached the levels seen in much of Asia, prevalence in the United States is rising quickly. A 2009 study showed that the prevalence of myopia among Americans between the ages of 12 and 54 surged from 25 per cent in the early 1970s to 42 per cent around the turn of the millennium.