ShmoopTube

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[Dino and Coop singing]

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Studying the human eye can be tricky business.

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And not just because people don't appreciate it when you start poking their eyes. [A pointed finger going towards a mans eye]

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It turns out the human eye has all sorts of complicated, delicate parts, that work together [Man shouts and scrunches up his face]

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like the components of a clock.

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But don't try to tell time with an eyeball. [Magnifying glass over an eye shows a clock mechanism]

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Again, people don't like that.

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We don't know why… [Girl looks annoyed]

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The human eye has one main function: to translate light into information that the brain can [Coop pointing at a blackboard]

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use.

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It all starts with the cornea.

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It's the transparent front part of the eye, and it's where light initially enters. [Light waves hitting the eye]

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It also helps the eye to focus, like a fancy camera lens. [Someone adjusting a camera lens]

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Though, unlike a fancy camera lens, you didn't have to pay thousands of bucks for your corneas. [Man holding lots of money]

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Or maybe you did….you clever, secret Cyborg, you…. [Mans face falls off and reveals his robot face]

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After the light passes through the cornea, it comes to the iris.

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You might know the iris as the colored part of the eye, but it also controls how much [A diagram of the eye with the iris shown]

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light gets inside.

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If the eye happens to be somewhere dark, the iris might open up real wide, to let in a [Pupil widens]

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lot of light…

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…but if it's bright out, it'll close up, letting in less light. [Pupil shrinks]

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It's kind of like the eye's bouncer.

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Well…it would be, if bouncers came in all sorts of pretty colors, like green, blue,

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and hazel.

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Next up on light's tour of the human eye is the pupil. [The bouncer turns people away]

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That's the black hole in the middle of the iris, and where light travels through to get

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inside of the eye.

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And sure, the iris might be doing most of the heavy lifting as far as opening and closing,

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but that doesn't mean the pupil doesn't do any lifting.

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Having passed through the pupil, the light slams into the lens: the second part of the [The lens is shown]

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eye that helps to focus the light, so that it can reach its final destination…

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…the retina.

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The retina does the hard work of translating the light into a bunch of signals that the [Dino pointing at a blackboard]

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brain can then understand.

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If it weren't for the retina, you'd probably need a translation dictionary from light language [Man on a surgery table]

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to brain language shoved into your skull. [Dictionary is shoved into the mans head]

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No thank you.

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That sounds painful.

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Once that light information has been translated into brain language, though, it still needs

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to actually get to the brain.

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And that's where the optic nerve comes in. [The optic nerve is shown]

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It's the superhighway that all that information speeds along on its way to the brain. [Coop pointing at a blackboard]

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And unlike regular highways, there are thankfully no twenty-car pileups along the optic nerve. [Pile of burning cars]

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So next time you're watching a YouTube video of a cat jumping in and out of a box, think

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about how much work it took your eye to get all that information to your brain. [Girl looks excited as she watches the cat video]

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And remember, your eye bouncer is always watching.

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So pick a good video. [The bouncer says "You should be watching Shmoop."]

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