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A falcon flies high above Earth. Suddenly, its sharp eyes spot a tasty mouse in the grass below. The bird dives down. Will it catch its dinner?

The mouse has sharp eyes, too. The eyes on both sides of its head can see almost everything around it. The mouse's eyes help it survive. Will it see the falcon and get away? One thing is for sure. Without eyes, neither animal has a good chance.

Animal eyes come in many shapes, sizes, colors, and numbers. Yet they all have the same job. They catch light. Then, with help from the brain, they turn light into sight. Human eyes work the same way. Look at this page. What you see is light bouncing off the page. The secret is in the rules of light.

Light is a form of energy, like heat. It can come from the sun or a lamp. Light is the fastest known thing. It can race from the sun to Earth in about eight minutes! It doesn't always go so fast. Water or glass can slow it down.

As light travels, it follows rules. It can reflect, or bounce off things. Sometimes, it is absorbed, or soaked up by objects. It also can bend. These rules affect how and what we see.

Right now, you are reading this article on your computer. Light hits the screen. Some of it bounces off the screen, or reflects. Part of this light moves toward your face. Now, your eyes get to work.

First, light hits your cornea. That's the clear covering over your eye. The cornea bends the light. How does it do this? Light slows down as it goes through the cornea. That makes light bend, or slightly change its path.

Next, light moves through your pupil. That's the dark center of your eye. Then, it passes through your lens. The lens bends the light, too. All this bending helps your eyes focus, or see a clear image.

The image shows up on your retina. It's like a movie screen at the back of your eye. There is one problem. The picture is upside down! Luckily, your brain flips it right-side up.

At night, your eyes need to work to catch more light. A muscle in the eye called the iris helps. It widens the pupil to let in more light. Parts in the retina, called rods, also help at night. Rods let eyes sense black, white, and gray. Each eye has 125 million rods!

Nocturnal animals have great night sight. Some have big eyes for the size of their heads. That helps them catch more light. Others, like cats, have an extra eye part. It's like a mirror. The eye catches light coming in and again when it bounces off the extra part. So a cat's eye is able to catch light twice!

Look at the picture of the prism above. It shows white light entering the clear glass. The glass bends and separates the colors of light. Now you can see a rainbow of colors!

When light hits an object, the object soaks in some of the colors. It reflects others. A leaf looks green because it reflects mostly green.

It takes more than light to see color. It takes cones. Cones are special parts in the retina. A person's eye has seven million cones! Cones sense red, green, and blue light the best.

When light hits the cones, it sends color messages to the brain. The brain mixes the colors together. That's how we see many more than three colors.

Some animals have different kinds of cones than people have. For example, scientists think a bee can see patterns made by ultraviolet light. Humans cannot see ultraviolet light. Animals with no cones at all, like the squid, only see black, white, and gray.

Animal eyes can be wildly different. Some have oddly shaped pupils. Some move in different ways. Many animals have two eyes. Others have dozens.

Why are they so different? Each animal catches the light it needs to survive. For example, a falcon's eyes are big for the size of its head. So are its retinas. That means its eyes can sense more light.

Also, the falcon's eyes are on the front of its head. They face forward. The falcon sees the same image twice, once through each eye. This type of vision helps the falcon know how far away the little mouse is.

Other animals, like the mouse, have eyes on the sides of their head. They can see in front, above, below, beside, and even behind their bodies. That may help them escape predators.

A clever chameleon can turn one of its eyes to look backward while the other eye looks forward. Just try sneaking up on a chameleon! Then there is the box jellyfish. It has 24 eyes dangling from its body! This may help it avoid hitting rocks as it swims.

Insects may have the wildest eyes of all. Look at the damselfly on the previous screen. Each of its eyes has many tiny lenses. These eyes are called compound eyes. Each lens catches light and makes an image. The bug's brain puts all the images together into one picture.

A fly's eye has 3,000 lenses. A bee's eye has more than 5,000. The dragonfly has 30,000! All these lenses help an insect see even the tiniest motion around it. That's one reason why some insects are hard to catch!

Today, scientists study all kinds of eyes. This gives them ideas for new inventions. Imagine an artificial eye that works just like the real thing! Eyes just might help us see a better, brighter future.

Article by Leslie Hall. Top-of-page illustration © Ivanagott/Shutterstock. "Seeing Eye to Eye" appears on page 2 of the September 2009 issue.