ELI5: Who do so many humans need glasses/contacts?
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Posted Jan 1, 2022, 4:45 PM UTC
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First off a lot of people who have glasses could more or less function normally without glasses. The main reason so many humans physically have glasses/contacts is due to increased access to healthcare including eye care.
However the reason so many humans need glasses/contacts is because modern society values being able to see finer details. For example there is usually an eye test you need to pass to get a drivers license or get certain jobs. Additionally humans are not doing themselves any favors by staring into screens (tvs, phones, computers,etc) for large portions of the day, the over exposure to light sources can damage the eye leading the need for glasses. Also diet/hydration habits can have a huge impact on your eye sight. And finally is survival of the fittest (or lack there of) in early history people with poor eyesight would have been killed off earlier but as the access to eye care has expanded people with bad eye sight have been able to augment their eyesight and live long enough to procreate and thus pass on any genetic predispositions for poor eyesight
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I have glasses and if I take them off im pretty much blind. I started getting blurry vision in middle school. For the most part my vision was blurry but I could squint and see pretty well. Naturally I hated wearing glasses and just walked around squinting which made my eyes worse. But what really made my eyes worse was spending hours in front of a computer screen. Now I make a living sitting behind a screen and my eyes continually get worse every year. I’m very close to being labeled legally blind, it sucks. If I’m stranded without my glasses somehow then I’m totally fucked
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I have astigmatism in my right eye. before I got glasses I would get migraines constantly, I'd walk in a zigzag, sprain my ankles approximately twenty thousand times a week and my writing on a piece of paper/board would slope up or down. ever since I started wearing glasses most of these issues are completely gone. glasses/contacts are truly awesome.
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It all comes down to evolution theory. The reason for someone's poor eyesight is in their DNA.
I have severe myopia (over -12D). Imagine me being born in the jungle 15000 years ago. I wouldn't be able to survive long enough to procreate and pass on my bad eyesight genes to my children. I would either first be preyed by a lion or in the very least I would be ostracized by my tribe for I would be a useless member of society. I wouldn't be able to hunt or do anything useful for my people, so I would have a low social rank and no other person would want to be my partner and have children with me. So, people with healthy eyesight would have a much higher chance of procreating and passing on their good eyesight genes to their children.
Now fast forward to 2022, I was born in a world where bad eyesight is not really a big deal anymore. There is no need to survive in nature because I live in civilization, and I still can be a functioning member of society because nowadays there is technology to fix shortsightedness and the skills I need to be a functioning member of society are very different from 20000 years ago and I am able perform them even with my bad eyesight, I can be a physician, a computer programmer, or a teacher and be very successful in current society. So I have much higher chances of having children and pass on my bad eyesight genes to them. That is why it is getting increasingly common for people to have bad eyesight, you don't rely on it to survive anymore neither in nature, nor in society.
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Actually in hunter societies short and long sighted people probably had their niches as long as the group was big enough to feed everyone. Long sighted is good for spotting pray, enemies etc at a distance. Short sighted is really good for finicky stuff, jewelry, weapon making etc. Granted -12 might be an outlier here :)
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At -12 they're basically blind even up close.
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Because we want to see as well as possible. It's like if everyone decided running marathons was the minimum standard for "running". Lots of folks would need "running aids".
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When you say running aids, you mean cars right?
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Cars, bikes, scooters, so many options.
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Other common species don’t have particularly great vision, like dogs. I’ve noticed that my dogs have varying amounts of near sightedness. They can get away with it due to their exceptional hearing and sense of smell.
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The eli5 is literally humans didn't evolve to see this many artificial lights and spend time focusing on narrow screens
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Partly due to the fact that we no longer rely on natural selection and actively "fix" any issues like this with glasses, contact lenses, surgery. If the poor eyesight is genetic, those traits get passed on to the next generation instead of being left out by way of that person not being able to reproduce.
We also subject ourselves to damaging conditions which would contribute to eyesight deterioration that might not happen in other species like digital screen time, extreme uv exposure , excessive alcohol, substance use and/or smoking to name a few
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Our eyesight deteriorates naturally over our lifetimes and some people's degenerates faster than others.
In the past you'd just be restricted as to what kind of work or activities you could do. Then corrective lenses were invented, and when they became easier and cheaper to manufacture everyone who needed them was able to get them.
More people need them than in the past too, because so many activities we do require decent eyesight. We used to ride or drive horses who had their own eyesight and didn't go terribly fast; these days we drive cars and have to have good vision and reflexes to do it. The literacy rate is higher than it used to be, so in the past not as many people would have cared if they couldn't see a street sign or a page of instructions because they couldn't read it anyway.
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My mom let brother and I outside all the time. He is only 11 months older than me. I am the only person in my immediate and extended family.. cousins, aunts, uncles, grandparents and my own children who doesn't need glasses. Imo genetics play an important role.
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If we lived in the wild and couldnt hunt because if bad vision humans with bad vision would die or not breed.
Modern humans figured out how to get around bad eyes with glasses and could have babies with bad vision.
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It's almost entirely down to environmental conditions in the modern world. To do the ELI5 part up front, spending a lot of time indoors in relatively dim light when you are a kid makes you nearsighted. This sometimes happens in other domesticated animals too, but it's rarely seen in wild animals or in humans that don't live in industrialized countries (many wild animals are naturally nearsighted as a whole species, but that's a different thing that some individuals being nearsighted and others not)
So for the complicated explanation:
Nearsightedness is caused by the eyes growing too long front-to-back, relatively speaking. This causes the focal point to be in front of the retina and the image on the retina itself to be out of focus. When you are young, your eyes are growing, and can easily grow too long. Under natural conditions, the light from a well-lit scene entering your eyes is focused on the retina, illuminating it and causing cells there to secrete dopamine, which in turn signals the eyeball to stop growing.
But if you spend your time indoors (which is much dimmer than sunlight areas even if we don't perceive it that way) your eyes don't get that bright light focused on them (because even when it's focused it isn't bright) and your eyeballs don't get the signal to stop growing. That makes them too long and that makes you nearsighted.
Not only can we demonstrate the components of this in animals, we can see it in how common nearsightedness is in different groups. It's vanishingly rare in hunter-gatherers. Its' quite rare in societies which aren't industrialized and don't have much formal schooling. It shoots up dramatically in the space of a few decades when societies go from mostly unindustrialized to mostly industrialized (Singapore, for example). In industrialized societies, there's a correlation between time spent outdoors and lower risk of nearsightedness.
That certainly explains the old “nerds” and glasses stereotype. Kids staying indoors to read books weren’t out playing in the sun so they end up with glasses more. These days kids stay indoors because tv, videoganes, or just straight up not liking being outside so the smart stereotype of glasses has kind of lost its edge a bit
Also in north america cities are designed in a way where kids can't or don't want to go out. Everything is so far apart and streets aren't designed with pedestrians and cyclists in mind. Cities where you could just let kids be outside for hours unsupervised for hours and you can be sure that they would be safe and have fun are literally illegal to build right now.
I wouldn’t say they’re illegal to build. The academics in architecture and urban planning have advocated for more walkable cities and towns for decades (in America).
It can be argued that’s it’s due to lobbying from automakers after WWII that led to highways being built through city centers instead of other more accessible public transportation infrastructure.
I mean, the zoning ordinances are set up in a way that when you build the massive suburban sprawls you can only make residental buildings, and commercial stuff must be built elsewhere which is always far away. The only option for people there is to take a car, so when cities are planned everyone assumes everyone will be getting around with a car and whoever doesn't use a car can go fuck themselves. If you haven't already I suggest checking out Not Just Bikes on youtube.
These days kids stay indoors because of covid. Pandemic would lead to more nearsightedness?
It could depending on how long it goes and how seriously people take it but I imagine if someone is prone to be outdoors, the pandemic isn’t going to completely stop them from going outside like someone who already rarely goes out to begin with
What baffles me is that we now know this, yet nothing is being done to expose kids to more light during those few critical years. Instead, they learn about things that will most likely not be of any use to them, while the nearsightedness will stay with them forever.
There's also genetic factors as well. I think this might be more along the lines of a cause, but it's pretty common for families to either need collective eye and/or teeth correction or not at all
Genetics can often make you more or less sensitive to environmental changes...and of course how your family acts can change your environmental exposure as well.
Maybe we should start having classes outside all the time, or build the schools with huge windows everywhere to let in a ton of light.
Is nearsightedness based purely off of being indoors too much as a kid? I was outside all of the time as a kid and I’m nearsighted
Did you attend public school?
Yeah
You need to be outside for 4 or 5 hours a day every day until you are 12 iirc.
Thanks for the explanation, it's fascinating. How would one explain farsightedness then? Is that not so much environmentally related?
Far sightedness later on in life is often attributed to the loss of muscular influence on the lenses of the eyes. The eyes need to work harder to focus on something closer to the face. This is why people with perfect vision can go on to need "reading glasses" later on.
What about far sightedness earlier in life? Used to not be able to read without glasses until about 14 when my eyes seemingly just got better. Maybe one case where all my time indoors was beneficial
I was wondering if the reverse is true. Like if nearsightedness means eyes grew too long, does farsightedness means eyes grew too short? And if we attribute environment to nearsightedness and long eyes, what do we attribute to farsightedness and short eyes?
Definitely can, but I only really know about presbyopia, which was described above.
Sometimes, but it's also caused by a cornea that's curved incorrectly. That seems to be genetically caused.
In the simple terms that I was taught, the lens becomes less flexible with age, so it's harder to change the shape of it to focus.
I think I was originally taught that it was the muscles, but I believe that you are correct. Perhaps my explanation is outdated
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Thank you!!!! That is so interesting. Explains why people who wore glasses were given that “nerd” “Poindexter” thing. Spent way more time indoors, learning, rather than outside, playing.
I thought they just didn't have the tool to correct people from non industrialized countries, I'm probably wrong though, but I guess that's the rational outcome to come with, but it's very interesting to read.
Follow up questions. what age does it stop at? Should I make sure kids have max brightness on iPad.
I don't have specific ages, sorry. But your eyes grow during the same time the rest of you grows, so it's basically the same age as height changes (for example) that the eyeballs are maturing.
Wouldn't matter, sunlight brightness is far beyond what you get indoors. A well lit office is about 500 lux, for example. Indirect sunlight is about 20,000. Direct sun is up to 100,000.
This is where it gets confusing. In Florida, we were always taught to wear sunglasses because our eyes will get damaged if we don't.
So should I make my kids not wear sunglasses until college?
Here's a paper that found light levels through sunglasses were still high enough to be protective against myopia.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6656201/
This is really interesting, do you know how/if they controlled for industrialized societies having both greater means to identify visual defects, while also having a greater amount of occupations and activities that would make said defects noticeable?
Some of this data comes from anthropologist surveys and the Singapore data comes from screening of drafted soldiers, which they have been doing for decades
So ample daytime outdoor exercise and play to prevent short sightedness? Around what age is this?
this is why i used to stare into the sun for long periods of time as a child.
checkmate, nerds.
Can't be nearsighted if you are blind!
I wonder if our large heads for our large brains are also a factor. We spend much more time in the womb to grow large brains but we still need extra time to grow our heads and brains much more than other animals do.
Problem is that some populations of people have very high levels of nearsightedness, others have very low levels, but they all have the same big heads.