YouTube: https://youtube.com/watch?v=qwQzTKHIkb4
Previous: What's Causing That Stitch in Your Side?
Next: Science Superlatives of 2015!

Categories

Statistics

View count:1,082,935
Likes:30,252
Dislikes:339
Comments:3,795
Duration:08:59
Uploaded:2015-12-30
Last sync:2018-11-22 14:00
While not the kind of epidemic you're used to hearing about, nearsightedness is becoming a major health issue in many places. Learn about how scientists are finding out the reasons behind the increase in myopia, and how sunlight might be an important component.

Hosted by: Michael Aranda
----------
Dooblydoo thanks go to the following Patreon supporters -- we couldn't make SciShow without them! Shout out to Justin Ove, Chris Peters, Philippe von Bergen, Fatima Iqbal, John Murrin, Linnea Boyev, Justin Lentz, and David Campos.
----------
Like SciShow? Want to help support us, and also get things to put on your walls, cover your torso and hold your liquids? Check out our awesome products over at DFTBA Records: http://dftba.com/scishow

Or help support us by becoming our patron on Patreon:
https://www.patreon.com/scishow
----------
Looking for SciShow elsewhere on the internet?
Facebook: http://www.facebook.com/scishow
Twitter: http://www.twitter.com/scishow
Tumblr: http://scishow.tumblr.com
Instagram: http://instagram.com/thescishow

Sources:
http://www.nature.com/nature/ebooks/summer-books/nature-summer-reads.pdf (pp 18-20)
http://www.npr.org/sections/health-shots/2015/10/08/446876198/firstborns-may-be-more-nearsighted-and-parents-may-be-why
http://www.npr.org/sections/goatsandsoda/2015/02/05/383765377/why-is-nearsightedness-skyrocketing-among-chinese-youth
http://archopht.jamanetwork.com/article.aspx?articleid=420394
http://archopht.jamanetwork.com/article.aspx?articleid=2448580
http://www.aaojournal.org/article/S0161-6420(14)01196-8/abstract
http://jama.jamanetwork.com/article.aspx?articleid=2441261
https://digitalcollections.anu.edu.au/bitstream/1885/10597/1/French_TimeOutdoors2013.pdf
http://iovs.arvojournals.org/article.aspx?articleid=2126968
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0127863
http://www.popsci.com/why-are-so-many-people-nearsighted
https://www.washingtonpost.com/news/speaking-of-science/wp/2015/11/16/scientists-hope-to-curb-the-nearsightedness-epidemic-with-eye-drops/

[Theme plays]

Michael: When you hear about an epidemic it usually has something to do with frightening viruses 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 40-50% 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 is 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 the light in front of the retina instead of right on it's surface. This creates and 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 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 nearsightedness 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 two out of 131 people in that community were nearsighted. That's one and a half percent. But the prevalence rose to nearly 50% 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 suggest it was the evidence 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 school children in Shaanxi, a middle income province, and the comparatively poor Gansu province. The prevalence of Myopia among the 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 that about 20% 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 that nearly 20% of that population is at risk for the serious complications mentioned, which can lead to blindness.

Having this many people at risk of serious eye problems is a major public health concern. And eye glasses will certainly help, so getting glasses to kids who need them is a big priority or at least it should be in these countries. But 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 that 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 everyday doing homework. If education is a factor in nearsightedness, this is where it's going to show up. To tease out the effect of cultural environment Australian researchers from the University of Sydney looked at six and seven 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 thirteen hours a week outside. The kids in Singapore? Only three. This seems kind of 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 affect.

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 German first tried to induce myopia in a set of chicks using special goggles, so that all 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 the 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 your body undergoes from low light nighttime vision, to daytime vision. And it's what lets bright natural light signal 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 of 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. The 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 preventative 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 nine hundred and fifty children in each bunch. The control schools didn't change their daily routine, but the other school 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 ore 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 school sent the kids outside for an extra 40 minutes, but the 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 that 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 just 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 looks promising. In the mean time, fresh air and sunlight as a clinical intervention is pretty appealing idea. In the en, it doesn't seem like video games or smartphones are to blame for this 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 just 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, brought to you by our patrons on Patreon. Like Casrton Steckle and Glen Knowles. Thank you both. And if you want to help us make more content like this just go to Patreon.com/SciShow. And don't forget to go to YouTube.com/SciShow and subscribe.