WEBVTT

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So we all know that the eyes
move around all the time

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to change what we're
looking at, but it's

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a little strange to think
about the pupil as moving.

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So why does the pupil move?

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Well, that's a good question.

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Well, the main reason
is that we need

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to have an optimal control on
how much light enters the eye

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and that's what the pupil
is doing by adjusting.

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So if you are in bright
light, then your pupil

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will constrict and get in the
right amount of light energy

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that is needed.

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Also, the eye wants
to be protected

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from excessive
exposure to light.

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But by regulating the size,
the diameter of the pupil,

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the eye is also working
a bit like a camera.

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You know, when you
use a camera and you

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use a very small size
of the camera's pupil,

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you're actually gaining
a lot in terms of depth

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of focus and resolution.

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So that is also important
to be able for the eye

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to adjust to that.

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Interesting.

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And so this has got to happen
pretty quick, because I mean,

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I know that our eyes work a lot
better than my phone camera.

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For example, where it's
like I'm continuing

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to tap it and refocus, refocus,
and it takes sometimes 10 to 20

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seconds to do that.

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The eye surely works
better than that, right?

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Yes, it might be
faster than you think.

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Let's demonstrate.

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Sure.

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So it took about a
fraction of a second.

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That's entirely normal.

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In fact, if it didn't
constrict quickly

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it would be a sign of something
wrong in the nervous system.

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Good to hear that I don't
have to go to the doctor

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anytime soon, then.

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