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Which part of your body lets you 

read the back of a cereal box, check 

out a rainbow, and see a softball 

heading your way? Which part lets 

you cry when you're sad and makes 

tears to protect itself? Which part 

has muscles that adjust to let you 

focus on things that are close up or 

far away? If you guessed the eye, 

you're right! Lets start with Light 

Waves...

What color is your iris?

Brown

Blue

Green

Hazel

Other:

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Your eyes are at work from the moment you 

wake up to the moment you close them to go 

to sleep. They take in tons of information 

about the world around you — shapes, colors, 

movements, and more. Then they send the 

information to your brain for processing so the 

brain knows what's going on outside of your 

body.

You can see that the eye's pretty amazing. So, 

come on — let's take a tour of its many parts.

Visible Light Waves 

Waves with a length of between 0.4 and 0.7 

micrometers can be detected by the human 

eye. For this reason we call these waves 

visible light. As you look around the room, 

everything you see has these waves 

bouncing off of them. If they didn’t, you 

would not be able to see them. What your 

eyes pick up and turn into a picture in your 

brain are these visible light waves.

Behind the cornea are the iris, the 

pupil, and the anterior chamber. 

The iris (say: EYE-riss) is the 

colorful part of the eye. When we 

say a person has blue eyes, we really 

mean the person has blue irises! The 

iris has muscles attached to it that 

change its shape. This allows the iris to  

control how much light goes through 

the pupil.

The pupil is the black circle in the 

center of the iris, which is really an 

opening in the iris, and it lets light 

enter the eye. To see how this 

works, use a small flashlight to see 

how your eyes or a friend's eyes 

respond to changes in brightness. The 

pupils will get smaller when the light 

shines near them and they'll open wider 

when the light is gone.

The pupil is the black circle in the 

center of the iris, which is really an 

opening in the iris, and it lets light 

enter the eye. To see how this 

works, use a small flashlight to see 

how your eyes or a friend's eyes 

respond to changes in brightness. The 

pupils will get smaller when the light 

shines near them and they'll open wider 

when the light is gone.

These next parts are 

really cool, but you can't 

see them with just your 

own eyes! Doctors use 

special microscopes to 

look at these inner parts 

of the eye, such as the 

lens. After light enters 

the pupil, it hits the lens. 

The lens sits behind the 

iris and is clear and 

colorless. The lens' job is 

to focus light rays on the 

back of the eyeball — a 

part called the retina 

(say: RET-i-nuh). 

The lens works much like the lens of a movie 

projector at the movies. Next time you sit in the 

dark theater, look behind you at the stream of light 

coming from the projection booth. This light goes 

through a powerful lens, which is focusing the 

images onto the screen, so you can see the movie 

clearly. In the eye's case, however, the film screen 

is your retina.

Your retina is in the very back of the eye. It holds 

millions of cells that are sensitive to light. The 

retina takes the light the eye receives and changes 

it into nerve signals so the brain can understand 

what the eye is seeing.

Rods and Cones Process Light

The retina uses special cells called rods and cones to process light. 

Just how many rods and cones does your retina have? How about 

120 million rods and 7 million cones — in each eye!

Rods see in black, white, and shades of gray and tell us the form or 

shape that something has. Rods can't tell the difference between 

colors, but they are super-sensitive, allowing us to see when it's 

very dark.

Cones sense color and they need more light than rods to work well. 

Cones are most helpful in normal or bright light. The retina has 

three types of cones. Each cone type is sensitive to one of three 

different colors — red, green, or blue — to help you see different 

ranges of color. Together, these cones can sense combinations of 

light waves that enable our eyes to see millions of colors.

Think of the optic nerve as the great messenger in the 

back of your eye. The rods and cones of the retina 

change the colors and shapes you see into millions of 

nerve messages. Then, the optic nerve carries those 

messages from the eye to the brain!

The optic nerve serves as a high-speed telephone line 

connecting the eye to the brain. When you see an 

image, your eye "telephones" your brain with a report 

on what you are seeing so the brain can translate that 

report into "cat," "apple," or "bicycle," or whatever the 

case may be.

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