The Nearsightedness Epidemic

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? Thanks for watching this episode of SciShow,
which was brought to you by our patrons on Patreon, like Carsten Steckel and Glen Knowles!
Thank you both! If you want to help us make more content like this, just go to
And don’t forget to go to and subscribe!


  1. I'm nearsighted in both eyes, but the left one is worse. I started noticing it after 4 years of working in a call center.

  2. Anyway to make a person farsighted to counteract myopia? Could an IR lamp imitate sunlight well enough to help at night?

  3. My guess is that it isn't the sunlight, but the outdoor time that forces the children to look at the DISTANCE. So they both have the near focus and the distance focus, which creates a great balance.
    If you wanna see far away, you have to see far away and train your vision. Just like a muscle needs to be stimulated to work, so does distance vision.

  4. Wait… he says : keep from, prevent, slow the progression…
    Bro I wanted to hear: will highly decrease, completely recover and treat to the completely normal eyesight 😩

  5. Is it possible that highly educated people tend to be wealthier, leading to a higher diagnosis of myopia than in less educated people, who may be of a lower income?

  6. the cause of myopia is diet, specifically too many carbohydrates. it has occurred
    recently, and across all cultures. the innuit are a good example. look it up.

  7. Cool, I’m farsighted, and I’ve never met anyone else who’s farsighted. This is probably why I can’t borrow my friend’s glasses when I need to read and forgot mine, but he can borrow just about anyone else’s 😂

  8. My eye doctor told me to do exercises….by focusing close, mid-range, then far. Being outside makes this so much easier.

  9. it sounds like kids spending time studying reduces dopamine, and by sheer lack of joy their eyes do not develop properly.

  10. Cause: repetitive close up work. That is called schooling. Inside and outside vision focusing would continually modify your eyes.

  11. There is also a widespread vitamin D deficiency due to people being exposed less to the sun…yet we also worry about skin cancer from too much sun. Does sunblock allow the beneficial properties of sunlight while still blocking the damaging rays?

  12. I've been nearsightedness since I was a kid… Been outside almost everyday when I was younger… Still wore glasses.

  13. Can increased sun exposure slow, stop, or reverse myopia? Could it be a beneficial treatment for people who already have it?

  14. My sibling 3 years older and higher educated and never outside and im less educated but im never inside. Hes about legally blind and i dont need glasses. I cant get enough sunlight.

  15. One factor you didn’t address is that when outside you’re essentially doing “far work” and flexing your eye to focus on things in the distance. This medium & far focus strikes me as the Yin to the “near work” Yang that balances their muscle development in and around the eye itself, resulting in healthier balanced vision.

  16. Oh man, that explanation of how near-sightedness works reminds me of how we needed to give the Hubble Space Telescope "glasses". 😆

  17. Hmmm that might explain why my vision has started to get a bit better since I got a full spectrum light on my desk for seasonal affect.

  18. Orrrrr maybe being outside = very little near work and practicing distance vision = less myopia. Sounds more likely than magical sunlight.

  19. Wait, so does this mean that people with dopamine-related disorders (mostly mental) are more likely to be nearsighted?

  20. I can probably vouch for that idea, within these past 5 years I'm always on my room, except when in class. I don't like the sunlight so I don't go out( just an excuse for having no friends). And I also don't like lights in particular, they somehow blind me(probably unrelated). I have 20/20 vision during my last eye check-up (6years ago), now I found myself reading things too close to my face. Sorry for broken english.

  21. Myopia doesn't always progress in the course of one's lifetime! I'm over 40 now and I have myopia and am nearsighted all my life! My lenses stayed at -1.5 to -1.75 diopter throughout the years and never did the nearsightness become worse! Now presbyopia is starting and I can read at close distance without my glasses on. So, saying that myopia always progresses in life, is wrong

  22. The solution is not sunlight but being outside. When you're outside, your brain has to focus your eye on objects at varying distances including really far away ones, so it can learn to decode and interpret the image correctly. During childhood development your brain thus learns how to obtain optimal focus so it can decode the best image at any given distance. When you're growing up inside, as most of us do these days, your eye only has to focus as far as the wall of the room you're in [windows excepted] and your brain doesn't have enough practice to learn how to set focus and decode images far away. The south Asian countries mentioned also have high population densities, which tend to result in even smaller living spaces, leaving even less focus training for your brain and eye. If those kids started living outside their myopia would improve, as shown by the Sidney example, since the brain can train the eye during development. For fully grown adults it's too late.

  23. my -7.75 sees you…or doesn't, at least very blurry. Don't see how that could work, I spent a lot of time outside, playing sports and what not. yet my myopia is far worse than my Mom's

  24. im pretty sure it also have to be with reduced horizons in modern society, more building around us, more time spend inside looking at fixed distances means our eyes just dont adjusts to depth as much as older generations, we dont look into the distance trying to make focus of far away objects as much. good news is if you kid wants to play videogames just send him with a laptop to sit outside on the sun

  25. im an outdoors person. i used to play outside till my mom made me come in. im still all about going outside..and my nearsightedness has always been bad. my whole family is plagued. also my husband is a master degree level engineer…he has perfect sight.

  26. I have high myopia and im going to be blind by the time im 30. Yay.
    Edit:i cannot do any thing to help it so its mostly guaranteed.

  27. I grew up in California and went outside a lot. I have perfect vision despite being pretty well educated. My mother grew up in Texas spending a lot of time outside, and lo and behold, perfect vision until recently. My father, by contrast, grew up in colder parts of the country and is nearsighted. So anecdotally it seems like there's probably something to this.

  28. Rubbish, I wear glasses, am short-sighted, my sister, who is the last is short-sighted, I'm the eldest, my second brother wore glasses(he's dead now) my mom wears glasses she's nearsighted as well. We all live in the Caribbean.

  29. I can say this is true. My vision was perfect until I hit middle school, where I quickly was just unable to see the board at the front of the class. That stuck till end of high school. Once I started college, I was outside more & my vision improved, and is still improving now; I don't need my glasses to do 99% of things. Now that's quite interesting. Really hope it is the sunlight.

  30. What if going outside makes your eyes focus on objects further away thus giving them the right kind of workout? Sunlight may have nothing to do with it.

  31. So… If medical professionals write prescriptions for everyone that we need decent food, sunlight, exercise, and shelter, can we use this to get people the basic amenities that current capitalism doesn't seem particularly invested in making available? I would petsonally love to be able to get medically demanded self-directed stress-reduction time. 🙂

  32. Before the invention of glasses only nearsighted people could read and write after age 40 or so. Before that stone toolmakers would benefit from myopia. Nearsighted people can focus closer. I'ts like always having a magnifying glass handy.

  33. I used to do all my homework, from age 11-14, with my head resting on my left arm, subsequently my left eye became significantly more short sighted than my right eye, to the point where I was having to wear glasses with a lense in the left side and normal glass in the right! (my right eye was mildly long sighted.) So near work does play a role!

  34. I was always out hiking as a kid and teen, going to the pool, and being outdoors in general. I became nearsighted at 13, despite the copious outdoors.

  35. The next step to research would be if sun protection (specifically hats & sunglasses that mean your eyes are effectively never getting direct sunlight) would change the effect of sending kids outside. Here in Australia the UV is so high you need to be careful about sun protection for the majority of the year, especially children as exposure in childhood is the biggest risk factor for developing skin cancer later in life, but apparently kids do better here than Singapore.

  36. How do you know our ancestors didn't have this "problem"" ? Wouldn't it be consistent with natural selection those who couldn't see objects at a distance well enough to hunt would die off ? Regarding the Sydney/Singapore study – did the researchers consider that when outside, the kids are looking at objects that are farther away ?

  37. Wait, isn't China covered in smog regularly, maybe there's too much smog to make a difference when they go outside.

  38. To me it seems that the obvious next step would be to develop indoor lights that simulate sunlight, preferably without the UV, or lower levels of it. And do tests involving those lights.

  39. Japanese child: "Dang you, homework, you are ruining my eyesight!
    American parent: "Dang you, Nintendo! you are ruining my child's eyesight!"

  40. So there should be a follow up done to see which exact spectrums of light are needed since the sun is hitting us with visible light, infrared, and ultraviolet. Light itself has dangerous and beneficial effects on our eyes. I work as an Ophthalmic Technician and use all three especially when preforming LASIK and PRK procedures.

  41. Hmmm, I stay a lot in my room, And my brother goes out a lot, but my brother has nearsightedness. I guess I'm just an idiot.

  42. This was a very interesting episode. However, I would be the exception to the paradigm. For my whole life, I've spent so much time outside that I have scars in my sclera. I'm also myopic.

  43. So… if a healthy dopamine cycle is important for healthy eye development, then in theory anything that interrupts or interferes with that dopamine cycle functioning should show some kind of adjustment in myopia rates. Would that mean we'd expect children with depression or other mood disorders, or who are neuro-atypical to correlate with myopia? Perhaps even children of abusive or traumatic upbringing? How much disruption is necessary for an effect to be seen? There's a lot to potentially unpack there.

  44. BREASTFEEDING. In developed countries women are relying on baby formula which is junk food for infants. Breastfeeding gives larger brains, larger skulls and more room in the jaw and eyesocket for rounded eyes and straight teeth. Larger, better developed brains also gives stronger, more interesting and alive personalities. reading, remembering and learning is so much easier. The test scores in the USA have lagged behind much poorer countries because baby formula cost money and poor women are not occupied with work so they stay home with the children nursing and breasting. Our great technological accomplishments here in America are not because we are a smarter race. It is because our high tech industries are peopled with scientist from The poor third world where breastfeeding is practiced by most mothers.

  45. Could it be…. artificial light.. seems how babies stare at light.. there heads are tilted up towards it and they just stare for days if they can.. But it can't be good. So people try keeping your kids from staring at bright lights. And like he said people didn't use to have this problem.. anyways I'd bet artificial light has something to do with it one way or another. Gut feeling.

  46. I've worn glasses most of my life. My vision at 65 is better now than any time before. I think it's because I don't use the glasses when at home,, or during daylight hours, when going out. My glasses are too strong now. My eyes have adjusted to focusing better at distant objects. I can read road signs, see individual leaves on the tops of trees. Sunlight does help.

  47. So…we want China to push their kids even harder in school. Because its pretty clearly not doing them much good, and it would mean an entire generation of a near-sighted military.

    Easy pickings.

  48. Not to put in a wrench I've worn photo Ray glasses for40 year's my vision is still getting weaker. So is it sunlight on the eyes photo lens prevent this. Thanks

  49. I’m nearsighted and I’m outdoors all the time . I’ve noticed that now that I’m older( 55) that I can improve my eyesight by not wearing my glasses or contacts . I feel it’s because I’m exercising my eyes rather than depending on a crutch

  50. So if myopia is developed by the elongation of the eyeball, do glasses actually repair myopia, or just hide the symptom until you need stronger glasses? (given that glasses just redirect light in a different spot, but the eye shape remains relatively the same)

  51. If the eye was able to change shape so easily, might going outside more often be able to help reverse the structural changes?

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