Exposure to sunlight may prevent myopia

We learn about the world mostly through what we see. Our eyes are our connection to the world.

Today, children watch shows on computer tablets or phones. It is common to see them engrossed in what they are watching on screens when their parents are doing other things.

Digital devices have become de facto babysitters. Children’s eyes are often focused on the screen as they watch shows, read or play games, making them oblivious to the world around them. They see what is near their eyes and fail to see the distance metaphorically.

In reality, it is interesting that many children can see objects that are near, but have difficulty seeing things that are far away — a condition called myopia or near-sightedness.

RISING INCIDENCE OF MYOPIA

The pervasiveness of severe myopia in Asia has more than doubled in the past 20 years and myopia rates have reached epidemic magnitudes in several parts of Asia.

The prevalence of myopia in Singapore is among the highest in the world.

In Taiwan, the percentage of seven-year-old children suffering from near-sightedness has increased four-fold to 21 per cent in less than 20 years. By the time they reach 15, an astounding 81 per cent are myopic.

Children who develop myopia early in life are more likely to progress to a more severe form. Myopic children complain of difficulty seeing distant objects, such as the writing on the screen or words on television.

This is not only a simple cosmetic issue that can be treated by wearing spectacles, but is also a risk factor for severe eye problems which can lead to complications and reduce vision.

Myopia treatment is very expensive and, in Singapore, a recent study showed that myopia cost almost S$1 billion annually.

The rising incidence of myopia is a grave public health issue, but what is the source of the problem? We know near-sightedness is less common in societies that are less focused on formal education and more on outdoor activity.

Near-sightedness is heritable but, interestingly, only 3 per cent of young children of Chinese ancestry in Sydney had myopia, a fraction of more than 29 per cent of those in Singapore, suggesting the rise in myopia rates must be due to the environment.

The common culprits include excessive near-sighted activities, such as reading, playing games on devices and watching TV. However, none of these common-sense factors are sufficient to explain the increase.

Australian Chinese are similar to their Singaporean counterparts. Perhaps, Singaporeans watched a little more TV, but the differences were trivial. There was, however, a big difference: Australian children were outdoors four times longer than Singaporean children, who spent only three hours outdoors a week.

Maybe sunlight is the key.

SUNLIGHT SEEMS TO REDUCE RISK OF MYOPIA

Monkeys may give us a clue. Myopia is very rare among primates, but the condition can be induced by keeping infant monkeys inside and away from the outdoors.

In sunny places such as Singapore, where the difference between outdoor and indoor light intensity is most extreme, perhaps myopia is more easily developed when children stay indoors.

In a study by the Singapore Eye Research Institute, each hour a teenager spent outdoors lowered the risk of myopia by 10 per cent. Interestingly, time spent on outdoor sports was also associated with reduced risk of myopia, but this was not seen for indoor sports.

Can increasing time spent outdoors make a difference? An elementary school in Taiwan required its 333 students to spend their break outdoors for a year to see whether this would reduce myopia rates. Another school served as a control group. The children in the first school spent a total of 80 minutes a day outdoors.

A year later, significantly fewer children developed near-sightedness at the school that mandated outdoor recess than those at the control school.

A study of 235 Danish schoolchildren with myopia showed the effect of sunlight on eye growth. The distance from the front to the back of the eye (increasing length means myopia is worsening) and vision were measured in each group of children at the start and end of different seasons. In Denmark, the length of the day can vary from 18 hours in summer to very few in winter. Among children with exposure to the fewest hours of daylight, eye growth was much more than that of those with long daylight exposure.

NO TV or IPAD, GO OUTDOORS

The tragedy is that TV, computers, tablets and video games have made the indoors too enjoyable for a child to resist.

The implications are obvious. First, parents should allow and make time for their children to play outdoors.

Second, perhaps schools should have students stay outdoors during breaks. Singapore is conducting a trial to test whether small incentives to increase the time children spend outdoors will reduce the risk of myopia. Results of the trial are not out yet.

Third, having the sun shine indoors at schools and other places where children play may help.

Doctors at the Singapore National Eye Centre have come up with a novel way to slow the progression of myopia. Clinical trials by the centre showed a very low dose of a drug, Atropine, slowed the progression of myopia by 50 to 60 per cent over a two-year period.

These simple treatments may help many children and, in theory, reduce the economic impact of myopia to a great extent. Drugs alone will not solve the problem and they are not without side effects.

However, in conjunction with more outdoor time, we can move closer to ameliorating emerging vision problems among the current generation of children.

ABOUT THE AUTHOR:

Professor K Ranga Krishnan is dean of the Duke-NUS Graduate Medical School Singapore. A clinician scientist and psychiatrist, he chaired the Department of Psychiatry and Behavioural Sciences at Duke University Medical Centre from 1998 to 2009.