How Your Eyes Work


KidsHealth presents
“How the Body Works,” with Chloe and the Nurb. [MUSIC PLAYING] [MUSIC PLAYING] Nurb, just because
eyeballs are the size of ping pong balls doesn’t mean
they make good ping pong balls. A nurb cannot be blamed for his
love of scientific exploration, my dear Chloe. It is what makes him a nurb. Then can we use the
eyeballs to explore how an eyeball works instead? We could, but these
are kind of small and– Squished. One might say that. How about we take a look at him? Most excellent idea. Let’s do. The eyeball is a
beautiful machine with lots of different
parts working together to let you see. Poets say the eyes are
the window to the soul. Well, the window to the
eyeball is the cornea, a dome of clear tissue
up in front of the eye that focuses light
as it passes through. Look at that
beautiful green eye. And brown eye. And blue eye. The colorful part is
called the iris, right? Yup. It’s right behind the cornea. In the middle of the iris
is a black circle called the pupil, an opening that
lets light into the eye. The iris has muscles
attached to it that change its size, making
the pupil bigger and smaller to control how much
light gets through. So the pupil gets smaller
when there’s a lot of light and bigger when it’s dimmer. Don’t look now, but I
think we’re being watched. Hmm. Ha! He blinked first. Which is a good thing. Blinking protects
and moistens the eye. Good point. So what happens
after the light has passed through the
cornea and the pupil? The light passes
through the lens. Like the lens in a camera? Precisely. The lens focuses the light
onto the back of the eye, where seeing really starts to happen. Can the lens in the
eye focus on stuff that’s close and stuff that’s
far, like a camera lens would? It sure can. Let’s head inside to see how. Last one through the
pupil’s a rotten egg! The lens is held
in place by a bunch of fibers, which are attached
to this ciliary muscles. (SINGING) Ciliary! Ciliary! Ciliary! The ciliary muscles
change the shape of the lens to let the eye
change its focus from something close by to something far away. What are you waiting for? Let’s get focusing! To see something near,
the ciliary muscle makes the lens the thicker. To see something far,
the ciliary muscles makes the lens thinner. From the lens, we
travel to the retina, the back wall of the eyeball. Right, because the lens focuses
the light onto the retina. The retina has millions of
light sensitive cells called rods and cones– about
120 million rods and 7 million cones in each eye. Whoa. That’s a lot of rods and cones. What’s the difference
between them? It’s the difference between
black and white and color! The rods see in black,
white, and shades of gray, and help us see the shape
and form of a thing. Rods also help us
see in the dark. And the cones see color? Cones are sensitive to one
of three colors– red, green, or blue. Together, they let us
see millions of colors, but cones need more light
than rods to work with. Hey, what’s this thing
behind the retina? Hey, no bouncing
on the optic nerve. It carries messages to the
brain about what you’re seeing. The rods and cones
change the colors and shapes you see into
millions of nerve messages. Then those messages are
carried along the optic nerve to the brain. It’s like your eye
is sending the brain a report on what you’re seeing. Then your brain
translates the report into cat, apple, or bicycle. Or– a ping pong ball! Hm? Keep your eye on the
ball there, Nurb. Oh! Ha ha, it’s on. [MUSIC PLAYING] [MUSIC PLAYING]

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