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.
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
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
||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.
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
- A great sight related experiment.
- Part of a great site by NJO that has good information on all types of
things, including sight.
- Bill Nye the science guy explains the eye!
||The Way The Eye Works
- This site is pretty much self explanatory.