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Introduction to Sight
From the moment you wake up in the morning to the time you go to sleep at night, your eyes are acting like a video camera. Everything you look at is then sent to your brain for processing and storage much like a video cassette. This is a very simplified explanation, but as you read on, you will discover why the sense of sight is actually considered the most complex of the five senses.

 How Your Eyes Work
Take a moment to locate an object around you. Do you know how you are able to see it? Would you believe that what you are actually seeing are beams of light bouncing off of the object and into your eyes? It is hard to believe, but it is true. The light rays enter the eye through the cornea, which is a thick, transparent protective layer on the surface of your eye. Then the light rays pass through the pupil (the dark circle in the center of your eye) and into the lens.

pupilsWhen light rays pass through your pupil, the muscle called the iris (colored ring) makes the size of the pupil change depending on the amount of light that's available. You may have noticed this with your own eye if you have looked at it closely in a mirror. If there is too much light, your pupil will shrink to limit the number of light rays that enter. Likewise, if there is very little light available, the pupil will enlarge to let in as many light rays as it can.  Just behind the pupil is the lens and it focuses the image through a jelly-like substance called the vitreous humor onto the back surface of the eyeball, called the retina.

 The retina, which is the size of your thumbnail, is filled with approximately 150 million light-sensitive cells called rods and cones. Rods identify shapes and work best in dim light. Cones on the other hand, identify color and work best in bright light. Both of these types of cells then send the information to the brain by way of the optic nerve. The amazing thing is, when they send the image to the brain, the image is upside down! It is the brain's job to turn the image rightside up and then tell you what you are looking at. The brain does this in a specific place called the visual cortex.

Because the eye is such an important and complex part of our body, we have many features which protect the eye. The eyebrows are the strips of hair above your eyes which prevent sweat from running into them. Eyelashes help keep the eye clean by collecting small dirt and dust particles floating through the air. The eyelashes also protect the eye from the sun's and other light's glare. The eyelids sweep dirt from the surface of the eye. The eyelid also protects the eye from injury. Tears are sterile drops of clean water which constantly bathe the front of the eye,keeping it clean and moist.

 Imperfect Eyesight
Not all people have perfect vision. People who can see things up close, but not far away are considered to be nearsighted. This happens when the light entering the eye focuses on a point in front of the retina. On the other hand, people who can see far away objects but not those that are up close are farsighted. Farsightedness occurs when the light that enters the eye focuses on a point behind the retina. Whether a person is nearsighted or farsighted, glasses or contacts help that person to see things much more clearly!

nearsighted eye farsighted eye

Sense-Sational Facts
Most people blink every 2-10 seconds.
Each time you blink, you shut your eyes for 0.3 seconds, which means your eyes are closed at least 30 minutes a day just from blinking.
If you only had one eye, everything would appear two-dimensional. (This does not work just by closing one eye.)
Owls can see a mouse moving over 150 feet away with light no brighter than a candle.
The reason cat's and dog's eyes glow at night is because of silver mirrors in the back of their eyes called the tapetum. This makes it easier for them to see at night.
An ostrich has eyes that are two inches across. Each eye weighs more than the brain.
A chameleon's eyes can look in opposite directions at the same time.
A newborn baby sees the world upside down because it takes some time for the baby's brain to learn to turn the picture right-side up.
One in every twelve males is color blind.

Sense-Sational Links
Optical Illusions - A great site that shows you how objects can play tricks on your eyes.
You Can Glasses - A fun site that talks about sight defects such as nearsightedness and farsightedness.
Sight Experiment - A great sight related experiment.
Your Body-Sight - Part of a great site by NJO that has good information on all types of things, including sight.
The Eyeball - Bill Nye the science guy explains the eye!
The Way The Eye Works - This site is pretty much self explanatory.

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