When you hear about epidemics, it usually has to do with some frightening virus like
HIV or Ebola.
So when scientists in the know start talking about an epidemic of nearsightedness, it probably
sounds … strange.
I mean, how can something that isn’t infectious or contagious become an epidemic?
And yet: The prevalence of nearsightedness in the US is pushing 40 to 50% among young
people.
And that’s nothing compared to parts of East Asia -- particularly Singapore, China,
Japan, and Korea -- where nearsightedness among high-school-age children is at 80% or
more.
Is it because kids these days have too much homework?
Or is technology to blame?
Are iPads ruining our children?!
New research suggests the cause of nearsightedness might not be peering too closely at your homework
... but neither is it all up to genetics.
And that might be a good thing, because there’s a potential prevention out there that’s
universal, and free.
The antidote to nearsightedness might be good old-fashioned sunlight.
Nearsightedness, or myopia, is a condition in which your eyeball is elongated.
When light enters an eyeball that’s too long, the lens focuses light in front of the
retina instead of right on its surface.
This creates an image that’s blurry if you’re looking at anything farther away than your
outstretched arm.
Myopia is easily corrected with glasses, contacts, or surgery.
But in extreme cases, what eye doctors call high myopia, it carries a risk of severe eye
problems, like glaucoma, retinal detachment, and cataracts.
Nearsightedness has always been around to some extent.
Astronomer Johannes Kepler blamed his near-sightedness on all of the writing and calculations he
did up close, and for centuries that’s been the conventional wisdom.
For a long time, peering too closely at written material, termed near work, has been blamed
as the cause of nearsightedness.
Near work typically includes things like reading and writing.
Watching TV doesn’t count, because it’s far enough away, and even using a computer
isn’t as hard on your eyes.
Things like smartphones and tablets are new enough that it’s hard to say whether they
should be included in the definition, but nearsightedness has been on the rise since
before they became mainstream, so they’re probably not at fault either way.
But while extensive studies have had a hard time ruling out near work entirely, they also
have a hard time establishing a firm link.
So, most scientists no longer think near work is directly responsible for nearsightedness.
But In the 20th century, we learned that there’s a certain amount of genetic influence on nearsightedness.
If your parents are nearsighted, you might be, too.
But that genetic influence isn’t really straightforward.
It involves a few dozen genes, each of which only contributes a fraction of the overall
story.
Plus, a study of an Inuit community in Alaska back in 1969 showed that nearsightedness can
spread way too fast for genetics to explain.
At one point, only 2 out of 131 people in that community were nearsighted -- that’s
one and a half percent.
But the prevalence rose to nearly fifty percent in their children and grandchildren!
Genetics couldn’t possibly be responsible for such a rapid spread.
This led scientists to conclude that, while genes have some influence, the main cause
of nearsightedness must be something in our environments.
And it must be something that’s dramatically increased in recent times.
While near work itself doesn’t seem to be the culprit, there does seem to be a link
between nearsightedness and education.
One study, published in October 2015 by researchers from Cardiff University in Wales, found that
firstborns are more likely to be nearsighted than later children.
About 10% more likely, to be specific, which certainly doesn’t account for the skyrocketing
prevalence, but it might provide a clue.
When the researchers adjusted the data to account for how much education the participants
had had, the effect diminished, which means that it was the education of the subjects
that made the difference.
The scientists suggested it was a result of so-called “parental investment.”
First-time parents who make their oldest kid hit the books might be a little more relaxed
by the third one.
As a result, firstborns who spent more time studying ended up being more likely to be
nearsighted.
Another study, by researchers from Sun Yat-sen University in China, compared the rates of
nearsightedness in two neighboring Chinese provinces.
They looked at schoolchildren in Shaanxi, a middle-income province, and comparatively
poor Gansu province.
The prevalence of myopia among kids from the wealthy province was roughly twice that of
the poor province.
The researchers couldn’t fully explain this difference, but higher math scores were associated
with higher rates of nearsightedness.
So it certainly looks like education correlates with nearsightedness, but how is this happening?
And if it’s so easy to correct, why worry?
Well the fact is, about 20% of people with nearsightedness end up having high myopia.
For example, more than 90% of 19-year-old men in Seoul, South Korea have myopia.
So that means nearly 20% of that population is at risk for those serious complications
we mentioned, which can lead to blindness.
Having this many people at risk of serious eye problems is a major public health concern.
And eyeglasses will certainly help, so getting glasses to kids who need them is a big priority
-- or, at least, should be -- in these countries.
But still that’s not going to address the underlying problem.
Why are so many people throughout the industrialized world nearsighted, when our ancestors didn’t
have this problem?
And why is the situation especially dire in Asia?
The best guess anyone has is that it’s related to the particular emphasis placed on education
by many East Asian cultures.
China has a do-or-die college entrance exam that makes the SAT look like a walk in the
park.
Kids as young as 10 spend hours every day doing homework.
If education is a factor in nearsightedness, that’s where it’s going to show up.
To tease out the effect of cultural environment, Australian researchers from the University
of Sydney looked at 6 and 7 year old ethnic Chinese children living in Sydney and Singapore.
The kids’ parents had similar rates of nearsightedness--around 70%--in both study groups.
But in the kids themselves, the difference was stark.
Only 3.3% of kids in the Australian group were nearsighted, compared to 29.1% in Singapore.
And the children in Sydney actually did more near-work activities, like reading and homework,
than the kids in Singapore, so that couldn’t possibly be the cause.
The only difference between the two groups of children that could account for the difference
in myopia was how much time they spent outside.
The kids in Sydney spent more than 13 hours a week outside, the kids in Singapore only
3.
This seems almost hard to believe.
Can sunlight really prevent you from becoming nearsighted?
Scientists and public health officials would really like to know.
But, nothing in epidemiology is ever simple.
In order to figure out if natural light can treat myopia, we need two things: Rigorous
evidence that sunlight really works, and a scientific reason--a mechanism--for it to
have that effect.
Fortunately, within the last few years, researchers have made progress toward both.
Experiments in animals, including chicks and rhesus monkeys, have shown that light can
protect against myopia.
Researchers in Germany first tried to induce myopia in a set of chicks using special goggles,
so that all the other variables could be controlled.
Then they exposed two groups to different lighting conditions, with one group being
raised under bright light that was meant to simulate sunlight, and others under normal
laboratory lighting.
Turns out, the onset of myopia was slowed in the group raised under bright lights, by
around 60%.
Then the researchers focused their attention on a substance produced by your own brain
that’s known to influence proper eye development: the neurotransmitter dopamine.
In another experiment, the researchers injected the chicks with a chemical that blocked dopamine.
Without the dopamine, the protective effect of sunlight disappeared.
So it’s believed that dopamine is released into your eyes as a result of bright light.
This chemical is at least partly related to your body’s day/night rhythm -- it’s involved
in the switch body undergoes from from low-light nighttime vision to daytime vision.
And it’s what lets bright, natural light signal to your body that it’s daytime.
So, researchers now think that this dopamine cycle is needed for healthy eye development
throughout childhood.
If it’s disrupted, like by spending all your time indoors in dim light, your eyeball
starts to become elongated, and myopia results.
This light-dopamine hypothesis is currently the best theory for how sunlight can help
your eyes develop.
Best part is, sunlight is free, and it’s an easy thing to try to see if it keeps kids
from becoming nearsighted.
A few studies have even looked into using sunlight as preventive medicine.
One of the biggest studies looked at primary school children at 12 schools in Guangzhou,
China.
They were divided into two groups of six schools each, with about 950 children in each bunch.
The control schools didn’t change their daily routine, but the other schools added
a 40-minute outdoor activity period.
Then the researchers tracked the kids for three years.
By the end of the trial, the incidence rate of myopia in the group that spent more time
outside was 30%, compared to 39.5% in the control group.
The reduction was actually less than what the researchers expected.
But still, preventing myopia in young kids is worthwhile, they say, because the longer
it progresses, the worse it gets.
The most difficult thing about using sunlight as medicine might just be convincing parents
to send their kids outside more.
In the Chinese study, the schools sent the kids outside for an extra 40 minutes, but
parents were also asked to send their kids outside even more on their own time.
But as far as the researchers could tell, the parents kind of...didn’t do that.
And they think more than 40 minutes is needed to achieve the most beneficial effect.
So, it seems like a victory for sunlight.
I mean, it isn’t established for sure -- many studies have shown that vision quality benefits
simply from going outside, rather than bright light per se.
So it could be that the effect comes from, say, playing more sports rather than sunlight.
But researchers are calling for more studies to better establish the link, and the data
so far look promising.
In the meantime, fresh air and sunlight as a clinical intervention is a pretty appealing
idea.
In the end, it doesn’t seem like video games or smartphones are to blame for the nearsightedness
epidemic.
But neither are books and homework.
And, thankfully, it’s not a terrifying virus that’s causing the epidemic of nearsightedness.
Rather, it might be an overwhelming cultural tendency to stay indoors.
So if you want to keep your kids from becoming nearsighted, maybe sign them up for soccer.
Sports: they’re good for you.
Who knew?
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