How do glasses help us see? – Andrew Bastawrous and Clare Gilbert

Almost 2000 years ago, the Roman philosopher Seneca peered
at his book through a glass of water. Suddenly, the text below was transformed. The words magically became clear. But it wasn’t until a millennium later
that that same principle would be used to create
the earliest glasses. Today, glasses can help millions of people
with poor vision due to uncorrected refractive errors. The key to understanding what that means
lies with the term refraction, the ability of a transparent medium,
like glass, water, or the eye to change the direction
of light passing through it. The eye has two main refractive surfaces: the cornea and the lens. Ideally, these surfaces work together to refract light in a way that accurately
focuses light onto the retina, the layer of light-sensitive tissue
at the back of the eye that works with the brain
to give rise to vision. But many people develop refractive errors, either during childhood
as their eyes are growing, or in later life as their eyes age. Imperfections in the cornea and lens cause refracted light to be focused
in front of or behind the retina, making images appear blurry. People with refractive errors
can still see color, movement, and light, but the details of what they’re looking at
are out of focus. People experience refractive
errors in different ways, owing to differences in their eyes. In some, light refracts too much, and in others, too little. Eyes with a focal point
in front of the retina are called myopic, or short-sighted. They can see close objects clearly, but those far away are out of focus. But when the focus point
is behind the retina, people are hyperopic,
or long-sighted. For them, objects close up
are unfocused, but distant objects are crystal clear. Finally, some people have a cornea
with a non-spherical shape that causes astigmatism, a form of out-of-focus vision
that makes all objects seem blurred, whether close or far. As we age, our eyes face new challenges. When we’re young, the lens of the eye
is flexible and can change shape to bring
images into focus, something called accommodation. This keeps objects in focus when we
shift our gaze from far to near. But as we get older, the lens becomes
less flexible, and can’t change shape when we want
to look at near objects. This is called presbyopia, and it affects adults starting
around the age of 40 years. Myopia, hyperopia, astigmatism, and presbyopia. Each of these is a refractive error. Nowadays we can fix them all with glasses
or contact lenses, which work by refocusing light
so it strikes the retina precisely. It’s even possible to correct vision
with surgery using lasers that change the shape
of the cornea and alter its refractive properties. But glasses remain the most popular. By using carefully crafted lenses to steer light to exactly
the right spot on the retina, a person’s clear vision can be restored. We’ve come a long way
since Seneca’s discovery and the crude glasses of yesteryear. In 1727, a British optician named
Edward Scarlett developed the modern style of glasses which are kept in place with arms
which hook over each ear. Today’s glasses take their inspiration
from that design, but they’re also much more precise
and personal. Each pair is tailored for an individual
to bring out their unique powers of sight. So if you’re one of the 500 million people
with a problem with close or far vision, or both, there’s a pair of glasses out there
waiting to reveal a whole new world that’s hiding in plain view.


  1. I never understood what people meant when they would say “I can only see things up close” or “I can only see things far away” because then there’s me and I just can’t see at all…

    Yes, I have an astigmatism 😂😂😂

  2. imagine how terrifying it would be if you see everything as blurry and cant focus on one thing, not even your phone

  3. Last week, friday, I made an appointment with the optologist because I thought I had myopia. Turns out I do. Left eye: – 0.75. Right eye: – 1.25. Today, just less than an hour ago, I got my glasses. The main difference has been leaves, where there was first colors, there's now precise outlines and I love it. I'm now 13 and it might get worse over time, but so far I'm grateful for science. Thanks!

  4. I have clear vision but i can do this thing were i put pressure on my eyes (i don't know how i do it) and it makes my vision blurry i want to know what's going on with my eyes have i do this

  5. Short sighted glasses person here

    People use my glasses and this is the reaction: Woah I got shorter
    Someone already short even said I wanna keep them I like being shorter

  6. I have a mild astigmatism in my left eye. This video just helped me understand that condition. Since the first thing I get asked is are you near sighted or far sighted? Now I know the answer. It's both lol

  7. How do overnight lenses work? I know they change the shape of your eye but I'm not exactly sure how it works relative to focal points.

  8. Well my eye problem is that ONE of my eyes sees close while the OTHER one sees far so that means they dont work together WHICH MEANS it takes for ever for my glasses to get made because each lens has a different amount of prescription :,(

  9. Randome person: hey can i try on your sPeCtAcLeS ( aka my glasses)

    Me: umm sure bu-

    Randome person:

    snatches wig i mean glasses
    puts them on

    Randome person: omah god im bLiNd HoW cAn YoU EvEn sEe in ThEm

    Me: omahgod bish

  10. My brother: take off your glasses then walk
    Me: (keeps walking into a wall because everything is blurred)
    My brother: ok have them
    Me: where the hek are you?

  11. when I went to the ophthalmologist to test my eyes he put some letters in a board far from me, and he said tell me what you see I started saying numbers: 3,8,6…. everyone started laughing 😂

  12. I wear glasses due to having a lazy eye. I finally got out of them after one surgery and a lot of years with them.

  13. I just cant stop crying because what i did to my eyes. Yes i dont watch TV or televisions very close nor far and i dont read in the dark, and even i play i have a great distance and over the years. 7years exactly i didnt notice that my eyes started to blur. I really miss my old eyes, i wish our body has the feature to restore vision by itself

  14. No one:
    Literally no soul at all:

    Me: is it just me or have I stumbled into the education side of YouTube again. And yet I literally watch these videos for no reason and get dumber

  15. I swear being on my phone a lot led to myopia and I have astigmatism in my right eye. My prescription glasses work. Everything is fuzzy with my right eye and everything is double vision with my left eye without my glasses. I never thought I would need glasses or anything, I used to hate them or the thought of them and now I need to wear them unless I want to look at 4 eyeballed two mouthed people.

  16. I'm near sighted. The best way I can describe it is going from 1080p with glasses on to 720p or 480p without glasses depending on how far away I'm looking.

  17. Automatic like for just the topic itself. Like how did Ted Ed know what people are silently thinking?

  18. Last year, i got new glasses, but the prescription barely changed, so my vision is bad even with glasses xD

  19. Before glasses I see pretty good, I don't need them
    puts on glasses WOW 4K vision ,cool man
    removes glasses I am blind !!

  20. I have made a discovery that when you pull back the skin of your face near your eyes, it focuses correctly, btw im near sighted, you have to squint and pull back the skin near your eyes

  21. Nice story, if all eyes were frozen box cameras – but they are not.
    The theory – is a complete failure.
    The words hyperopia and myopia, are tied to that theory failure.
    The failure is this.
    From birth, the normal eye controls its refractive STATE, to its AVERAGE value of ACCOMMODATION.

  22. The ending reminds me of the time I got glasses for the first time and was commenting on EVERYTHING I saw. I had a field trip to the zoo the next day and my dad told me, "You might see some animals you had no idea existed. There's a brand new world for you to discover."

  23. Myopic and astigmatism here. Since there is no contact lens for astigmatism yet, sometimes I still need to wear glasses eventhough I wear a contact lens LOL. Can't see things clearly especially at work when I have to face laptop for hours xD

  24. I have astigmatism and also will see double sometimes if my don’t wear my glasses. Idk why that is but feel free to tell me.

  25. I have no problems with my eyes but I want to wear glasses because I think they look so cool but I've read some of those comments and now I understand those people that actually wear glasses want to get rid of them so idk maybe I'll not spend my money on a bunch of artificial glasses that do nothing

  26. I have a question: People with low-far-away visions, can their eyes recover on it's own soon? Especially when you use glasses….?

  27. I love when people call me "Four eyes" because they're just insulting themselves and saying that I can see way better than them

  28. I hate when people put up a number and ask "What number am I holding up?" Its not like I cant see it- my vision is just blurry you uncultured swine

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