Episode 6 - How Do We See?

Our eyes are our windows to the world. From the moment we wake up, they are hard at work informing us of our surroundings. Learn about the parts of the eye and how our eyes create 3D vision.

Materials:

• two people
• some coins or buttons
• a cup
• an eye patch (you can use your hand if you don’t have an eye patch)

Instructions:

1. Have one person sit in a chair at one side of a table. With the eye patch, or their hand, covering one eye.
2. Put the cup on the table, about two feet away from the person.
3. Have someone hold a coin in the air about 1.5 ft.(45 cm)above the table. Move the coin around slowly.
4. Ask the person with the eye patch, to say “Drop it!” when he or she thinks the coin will drop into the cup.
5. When they say “Drop it,” drop the coin and see where it lands.
6. Try it again with the cup farther away. And again with the cup closer. And again without the eye patch.
7. Compare the results of several different drops.

Eye Facts:

1. The eye is like a ball that’s full of liquid and other very special parts that allow you to see.
2. At the front of your eye is a protective cover called the cornea.
3. Right behind the cornea is your iris. The iris is the colored part that can be a shade of brown, blue, green or hazel. The iris has two muscles. The dilator muscle and the sphincter muscle. The dilator muscle makes the pupil get bigger. The sphincter muscle makes the pupil get smaller. When light is bright, the pupil gets smaller so less light gets in. When it’s dark the pupil gets bigger so more light can get in.
4. Inside of the iris is an opening called the pupil. That’s the black dot in the middle of your eye. It lets light go into your eye so you can see things.
5. Just behind the pupil is the lens. It focuses on the things you see. When the lens inside your eye needs to focus, strong muscles pull the lens to make it longer or shorter.
6. After the light is focused by the lens, it shines onto the back of the eyeball, onto the retina. The retina is connected to your brain by nerves. The retina has millions of tiny photoreceptors on it.
7. Photoreceptors are cells that are sensitive to light. There are two types of photoreceptors. Rod cells and cone cells. Rod cells are sensitive to light, but not color and cone cells are sensitive to both color and light. There are about 120 million rod cells on the retina. There are only about 6 million cone cells on the retina.
8. The retina gathers all the information about what you are looking at and sends it to your brain through the optic nerve.