Why Don’t Other Animals Wear Glasses?

Why Don’t Other Animals Wear Glasses?


[MUSIC] This episode is supported by The Great Courses
Plus [MUSIC] I’ve never seen a gorilla with glasses,
a chameleon with contacts, or a moose with a monocle. Although I did see a spectacled
bear once. But like 7 out of 10 Americans, my eyes don’t
bend light correctly, so I’ve worn glasses since fifth grade.
It’s a confusing question: How did our species survive the trials of natural selection if
so many of us can’t see? We can’t take otters or ostriches to the
ophthalmologist, so it’s hard to know exactly how common bad eyesight is in the animal kingdom. But if you can smell, hear, or feel your way through life, good eyes are expendable. Many species that rely on seeing sacrifice clear vision all over to see extra-sharp where natural selection demands. For most visual species, you’re more likely
to become a meal before you pass on your blurry genes, so they vanish from the population. But modern humans live a pretty comfortable
life, so natural selection has let us slip through with bad eyesight. The lens inside your eye isn’t rigid—more
like really firm Jell-O. It’s made from flexible proteins called crystallin. They let visible wavelengths pass through, but the lens’s rounded shape bends the light. Refraction: just like what happens where air meets water. We can’t focus by moving our lens closer
or farther from the retina, the way a camera would. We actually squish and pull our lens
to change how it bends light. Now, objects reflect light in all directions. The farther away an object is, the angles between the light rays entering our eyes are smaller,
and our lens doesn’t need to bend them as much, so tiny muscles relax and flatten it. As an object moves closer, light rays are hitting our lens at wider angles, so muscles
squeeze the lens into a rounder shape to bring the focal point right onto the retina. We do all this involuntarily—healthy eyes
can focus from infinity to here in less than half a second. But in many of us, this process doesn’t
work perfectly. People with myopia, or nearsightedness, have trouble focusing on objects far away, often because the eye is too long—kind of football-shaped. The lens focuses the image
in front of the retina. Or if you have astigmatism, like me, your cornea is too round, producing
weird blurry effects. This is corrected by using a lens that spreads
the light out just a tiny bit before it enters the eye. The focal point now hits right on the retina. If the eye is too short or the lens can’t
quite squish into a round enough shape, the focal point moves behind the retina when trying to view things up close. We call this hyperopia, or farsightedness. And it’s corrected using
a lens that slightly focuses the light in front of your eye—kind of like wearing tiny
magnifying glasses. As we age, people often get presbyopia: our
lens becomes less elastic, unable to squish enough to bring the closest objects into focus. If somebody already requires distance correction, often they’ll be be fitted with bifocals
or contacts with two different types of lenses: one for far and one for near. Contact lenses correct these problems the
same way as glasses do—you just don’t notice the different lens shapes on the tip of your finger. Corrective surgeries like LASIK don’t actually work on your lens. They use lasers
to reshape the round cornea in front of it, adjusting how it naturally bends light. Strangely, over the past half century, eyesight
is getting worse in developed countries. 60 years ago, nearsightedness affected 1 in 10
Chinese people, but today it affects 90% of the younger generation. In Seoul, Korea alone,
97% of 19-year-old males need corrective lenses. The change is too fast to be due to just genetics.
It was originally thought that the culprit was too much time spent reading or staring
at devices up close, but newer research suggests that the biggest risk factor could be kids
spending less time outside under bright sunlight. So how good can our vision get? Could we see
like eagles? When our lenses—natural or prosthetic—are just right, the limit of human vision
is lower than 20/20—actually closer to 20/8. Professional athletes in visual reflex sports
like baseball are often down in this range. The limit to our vision doesn’t come from
being able to bring things into focus; it’s because the cone cells on our retina are only
packed so close together. Like pixels on a camera sensor, we can’t pick up detail smaller than a single cell. Birds of prey like hawks have more tightly
packed cells on their retinas, so they can see more detail than we can. What’s strange is people who have had their
natural lenses removed can see expanded wavelengths, down into the ultraviolet range. Claude Monet,
the artist, was one of these people. We made a video about him; you should check it out. We might not ever see like Superman, but thanks
to physics, we can bring our vision into focus. Stay curious. Thanks to The Great Courses Plus
for sponsoring this episode. The Great Courses Plus is a service that allows you to learn about a range of topics from educators, including Ivy League professors
and other schools from around the world. Go to thegreatcoursesplus.com/ok and get access to a library of different video lectures about science, math, history, literature… or even how to cook, play chess,
or become a photographer. New subjects, lectures, and professors
are added every month. Let’s say you wanna know what happens to
your vision after your eye— they’ve got a course called Understanding the Brain. With The Great Courses Plus, you can watch as many different lectures as you want—anytime, anywhere— without any tests or exams. Help support my show and start your one-month trial
by going to thegreatcoursesplus.com/ok. Unlike most viruses, not only can Zika cross the placenta from mother to child— but we now know it specifically targets developing brain cells. Worse, Zika also kills radial glial cells, which normally act as a scaffold to shape the developing brain. There’s no treatment or vaccine, and symptoms are usually so mild that most people don’t even know they have it The World Health Organization has resorted
to telling women in Zika-affected areas, “don’t get pregnant”—which is a pretty good sign
we don’t have any good options.

100 Replies to “Why Don’t Other Animals Wear Glasses?”

  1. How well does Laser Eye surgery work? It’s just that I’m quite young and although my prescription is very small (tiny, really) it gets worse every time I visit the optician’s. I don’t want to have terrible eyesight by the time I’m, say, 50.

  2. I have very mild nearsightedness but my astigmatism is worse.

    It gets worse for me after every blow to the head I get (active teen and very unlucky when it comes to cars I’m passengering in). And I’ve not gotten an eye exam since my last concussion. But my glasses still work 90% of the time.

    My optometrist said it probably gets worse after a blow to the head due to internal pressure changes bulging the lense and it doesn’t fully return to normal. And is why blurry vision is a post concussion symptom

  3. 1:32 I can actually do a thing where I can stop seeing in HD and make everything look like a blurry mess of circles. Is it because of this or just because I can change the size of my pupils at will? I havent ever heard of anyone else doing that, so maybe it’s unique to me? Or then it’s a thing all humans can do? Interesting. 🤔 Tell in the comments if you can do that too.

  4. Because animals lack money to purchase glasses, and lack the necessary limbs or motor control to put glasses on, let alone manufacture them. Furthermore, humans do not often manufacture glasses suitable for animals, and the few times we do, they are meant as exhibits rather than for actual wear.
    Does it really take six minutes to explain this?

  5. Because they don't have arms to put it on lol and I have glasses because would have a lazy eye if I didn't my right without glasses and my left eye shut everything is blurry

  6. I went outside a ton as a kid and i still do (well I'm still a kid/teen depending on what age you cant as a teenager)
    but I'm still near sighted
    maybe it comes from my genes or soemthing

  7. You made it seem like myopia and astigmatism are both corrected the same way (i.e. with a simple minus lens) rather than astigmatism requiring a toric lens. What gives?

  8. As usual, click bait without answering your initial question. Next time call it “why do humans seem to need more glasses these days?”

  9. Animals can’t wear glasses because the glasses wouldn’t fit, most animals ears are too high up there head so the glasses would be bent and the animals wouldn’t be able to move there ears. Also animals don’t have enough money to buy glasses so it just wouldn’t be a profitable business to make animal glasses. Thanks for your time

  10. Not sure if I buy the sunlight thing. There’s like very few actual health benefits to going outside in the sun. Skin cancer and damage can happen regardless of sunscreen and the best way to prevent this is to stay inside. Also, vitamin d is meant to be consumed from the diet, not necessarily from the sun. I just don’t think it’s prudent to encourage sun exposure, especially in young children.

  11. Well lots of animals don't have very good eyesight but manage without it….

    Like in humans sight is our primary sense. It takes up 30% of the sensory area of our brain. Even our furry friends have different sensory priorities. Cats and dogs rely far more on their sense of smell and sound than sight. And cats are quite adept with their sense of touch, proprioception, proximoception, etc. To the point that a blind cat is able to adapt incredibly well, the way they move around you'd never know they're blind!

    (Also like: ferrets for example have terrible eyesight. They're still great hunters tho!)

    Even without my glasses I can see something moving, it's not clear or sharp, but I can usually make out what it is. I mostly need my glasses for details; which as a human being who reads – and needs to be able to read signs at a distance. So details are important to my day to day life, albeit not survival.

  12. I've worn glasses for 5 years now. I thought it was all due to being in front of the TV or laptop so much. I guess I was somewhat right.

  13. Uh cause they are animals and the concept of vision correction can’t even start to be understood by animals? Stupid video.

  14. Living indoors->overfocusing your eyes->myopia
    Animals dont live indoors,they tend not to focus on something rather than scanning all the area(unlike us who read letters or play games) and of course….they cant make glasses

  15. Since natural selection let us slip through with bad eyesight due to our cozy lifestyle, does the same go for domesticated animals or pets?

  16. Some of the information in this video is incorrect.
    1. The majority of the refracting power of the eye is from the cornea, approximately 45 diopters worth while the lens is only approximately 15 diopters worth.
    2. We don't "squeeze and pull" the lens. The lens has a certain shape that it "wants" to be in, or it's relaxed position, that which allows us to see farther objects and it is the more rounded shape. When we focus with the lens to see objects up close to us, the ciliary muscle pulls the lens to flatten it.
    3. Astigmatism is not caused by the cornea being too round. Instead it's because the cornea has different refracting powers in different meridians. For example, the cornea may have a different refracting power at the up/down meridian versus the left/right meridian. A lot of people are worried by the diagnosis of astigmatism. But in reality the majority of people have at least some astigmatism, something like >80% of people.

    My source? I am an eye doctor…

  17. I wear glasses too , last month they broke and I had to keep repairing them until I got my new ones , I was basically blind for 4 days before I got my new glasses because my old ones broke even more so I gave up trying to fix old ones , I’m legally blind

  18. I've had glasses since fifth grade too. The worst thing is that my sight levels change a lot, and I have to wait many months before getting them corrected on average.

  19. I started wearing glasses when I was in kindergarten (5 years old). I have ~20/25 vision (with my glasses), and ~20/75 (?) without. I’m very, very nearsighted. Anything past 1-1 1/2 past my eyes is blurry. I also have astigmatism, so that’s great. My vision’s only getting worse. In a few years, I’ll probably be able to say that I’m legally blind.

    Oh, yeah, another fun fact: my phone is about 3-3 1/4 inches away from my face right now. It’s blurry.

    My left eye is worse then my right. So, I have a slight double.

    Thanks, Mom, for giving me terrible eyesight.

    Now then, if you’ll excuse me, I’m gonna put my eyes back on.

  20. But being a little nearsighted is helpful to literally focus on reading and precision work like soldering. Try taking a photo up close and you will see the image gets blurry

  21. Here is a question that's been bugging me. When you close your eyes sometimes you can see flashes of color and waves some times kaleidoscope. Blind people can "see" this too even if theyve always been blind. And it is known that humans can't see all the colors. We can also produce images in our brain that we haven't seen irl. Which brings me to my question: Can we imagine colors that we can't see or produce images of colors invisible to the eye in our brain? And how if possible?

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