Human Eye - How The Eye Works and What are Rods and Cones?

Your eyes are like two tiny movie cameras inside your head.
They are sending a steady stream of pictures back to your brain, like a television camera sending live pictures back to a TV screen.
Human Eye
Your eyes have a part called the lens, just like a camera. The lens helps to bring everything you look at into focus, so that details are as clear as possible.

What are Rods and Cones?

Human beings are luckier than many other animals because they see in color. Some other animals, such as birds and butterflies, can also see colors.
To see colors, we have special cells in the eye called cones. 
They share the work of seeing with other cells called rods.
Rods do not detect the difference between colors and don’t need as much light as cones to make them work.
So at times, rods are more useful to you than cones, such as at night when the light is very dim.
Have you ever been for a walk in the moonlight and noticed how pale, silvery, and colorless everything seems?
Photographers can take pictures by moonlight which are just as colorful as pictures taken by day. So the colors are still there by moonlight, but we can’t see them.
Can you think why this is?
The cones help us to see color, but moonlight doesn’t provide them with enough light to function well at night.
What are Rods and Cones

 What Is Stereoscopic Vision?

When we use both our eyes, we have a kind of sight called stereoscopic vision. 
Because both eyes are at the front, they both see the same object. But your eyes are a little apart from each other, so each has a slightly different view of things. 
You can check this if you place two objects, such as drinking glasses, on a table in front of you. 
Place one about 8 inches (20 centimeters) away from you, the other 2 feet (60 centimeters) away. 
Put your chin on the table with the two glasses in a straight line away from you. 
Close one eye, then the other. 
Do you see exactly the same thing with both eyes?
Your brain makes use of the fact that your eyes tell different stories. 
By comparing the messages from each eye, your brain works out how far away an object is. 
Your brain does this in a split second every time you look at anything.

Stereoscopic Vision Test for kids

Why are our eyes on the front of our head, both looking the same way? 
It seems a waste of an eye, doesn’t it? 
To discover the answer, play this game of throwing and catching a ball with a friend.

You will need:
  • stiff, black paper or cloth
  • scissors
  • a sharp pencil
  • a ball
  • thin elastic or ribbon
Stereoscopic Vision Test for kids

1.Cut out an eyepatch from the paper or cloth. Using the pencil point, make a small hole on either side of the patch. Thread the elastic or ribbon through the patch.
2. Play at catching the ball with both eyes first. Throw the ball 20 times, and make a record of how often you drop the ball.
3. Now cover one eye with your patch. Keep a record for another 20 catches. Did you do as well? Explain what happened.

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