Page 126

 Eyeball

R2R (page 126)

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.
-The colorful part is called the iris right?
Yep, 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 is a lot of light and bigger when its dimmer. 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 on to the back of the eye where seeing really start to happen.
-Can the lens and the eye focus on stuff that’s close and stuffs that far like a camera lens would?
It’s sure can. Let’s head inside to see how. Last one through the pupil is a rotten egg. From the lens we travel to the retina. The back wall of the eyeball.
-Right, because the lens focuses the light on 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.
-Wow, 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 grey. 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?
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 message, then those messages are carried along the optic nerve to the brain.