Asia study ethic blamed for myopia
Staying indoors, poring over books and "intense" levels of education have been blamed for an epidemic of short-sightedness sweeping across eastern Asia.
Myopia, or short-sightedness, now affects between 80% and 90% of school leavers in the major cities of countries such as China, Japan and South Korea, say experts.
Between 10% and 20% of sufferers are said to have "high" myopia, which can lead to loss of vision and even blindness.
Writing in The Lancet medical journal, Professor Ian Morgan, from the Australian National University in Canberra, and colleagues suggest that the powerful Asian education ethic may be largely responsible.
Recent evidence suggests short-sightedness is to a great extent due to environmental rather than genetic factors. Numerous studies have shown a link between close reading and intensive study and myopia.
The experts wrote: "The rise in myopia prevalence in urban east Asia might therefore be plausibly associated with the increasing intensity of education. Moreover, east Asian countries with high myopia now dominate international rankings of educational performance."
One Australian investigation, the Sydney Myopia Study, showed that children who read continuously or at a close distance were more likely to be short-sighted.
More recent work had indicated that increased amounts of time spent outdoors may protect against myopia. "The protective effect seems to be associated with total time outdoors, rather than with specific engagement in sport," said the experts.
Greater exposure to sunlight may protect eyesight by stimulating the release of retinal dopamine, a "neurotransmitter" involved in nerve signalling.
They added that genetic factors also played a role in myopia risk. The contribution made by many small-impact genes, and gene-environment interactions, was yet to be established.