|"Turn your face to the
Sun and the shadows fall behind you."
- Maori proverb
When light reaches the Earth's surface about 69% has been reflected, refracted, and absorbed by over a dozen different types of surfaces before we see it. Each time sunlight strikes a surface it is changed by the properties of that surface making certain colors stand out more than others.
Sunlight allows a person to see by helping us distinguish between colors. A thin layer of nerves called the retina line the inside two thirds of the eye. The retina is made up of a colored film that absorbs light and thousands of tiny nerves, which monitor the colored film for changes.
The colored film contains photosensitive substances called scotopsin, rhodopsin, and photopsin. When light strikes one of these 3 pigments, the pigment releases energy as it is chemically broken down. This energy stimulates tiny nerve endings called rods and cones. Because rods respond to small amounts of light our eyes can see at night. Cones allow our eyes to see the colors red, green, and blue in response to bright light.
There are about 7 million cones and 70 to 140 million rods in each eye. Most cones are located in the center of the retina and make up the sharp area of vision called the fovea.
A pair of Eskimo "sunglasses" can be cut from a piece of bark, leather, plastic, or heavy cloth by cutting a narrow slit in the center of the material. The narrow slits reduce the amount of reflected light into the eye from snow.
Stimuli from the rods and cones travel along nerves from the eye by way of the optic nerve. At the point where the optic nerve leaves the retina a blind spot occurs; this is because there are no rods or cones there to "see" light. This blind spot is called the optic disc or scotoma.
Before the optic nerve reaches the brain, it divides the incoming images from each eye and sends the left field of vision from both eyes to the right side of the brain. The right field of vision from both eyes goes to the left half of the brain. All of this occurs in the smallest of milliseconds.
Each nerve carries information from a point on the retina to its pair point on the outer cortex of the brain, creating "pictures" of what our eyes see. The brain processes these images and identifies them.
©Copyright 1998 Elizabeth
Beckett, Holly Bernitt, and Vishwa Chandra.