Transcript The Eyes Have It! - Somers Elementary School

The Eyes Have It!
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2007
Light, Lens, Action!
• 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.
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2007
How the Eye Works
• 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.
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2007
How the Eye Works continued
• Your lens in your eyes change size all the
time. When you look at objects real close up,
the lens gets thicker. If you look at objects
far away, it gets thinner. It does this to help
you focus the correct image on the retina.
• After light passes through the lens it shines
through the vitreous humor to the back of
the eye where it hits the retina. The retina
takes the light and changes it into nerve
impulse so the brain can understand what
the eye sees. It sends the message to the
brain by way of the optic nerve.
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2007
Parts of the Eye
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• Cornea: The cornea is a clear white
covering over the outside of the eye. It helps
the eye focus like a lens on a camera.
• Iris: The iris is the part of your eye that has
color. It gets bigger and smaller to let in
different amounts of light.
• Pupil: Black opening in the middle of the
eye. Light comes through this opening.
• Aqueous humor: The aqueous humor is
clear water-like substance that keeps your
eye clean. It also provides nutrition.
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• Lens: The lens bends light. This helps the
eye see close up and far away things.
• Vitreous Humor: The vitreous humor is
clear water-like substance in the back of your
eye.
• Retina: The retina has nerve cells called
rods and cones that detect light. It is in the
back of your eye.
• Optic Nerve: The optic nerve carries
electrical signals from your retina to your
brain so you can see.
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2007
Rods and Cones
Rods and cones are special
cells that process light.
Rods and cones are extremely
small. In fact, there are about
120 million rods and 7
million cones in each eye!
Rods help us see black and
white and shades of grey.
Cones help us see color. You
have three kinds of cones
are - red, green, and blue.
These cones work together
to help us see millions of
colors.
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Flipped Image
• When you see
images, they turn
upside down when
they hit the retina.
So your brain sees
everything in the
world upside down.
Your brain basically
flips everything
around so it is right
side up again.
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2007
Eye Movement
There are the six small muscles that move each eye from side to side, up
and down and on the slant. When these muscles don't work together, it can
affect vision. One condition that can arise when these muscles don't work
together is “lazy eye”, a condition that affects about 5% of children and
arises when the eye muscles don't work together properly. This leads to
"lazy eye," in which one eye takes over all the vision duties.
A defining characteristic of these tiny muscles is that they are nearly always
moving, even during sleep. In fact, even when "staring" at a fixed object,
the eyes keep moving over the image. Although these muscles are very
small, they use a lot of energy because they are always on the go.
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2007
Protection 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.
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Imperfect Eyesight:
Nearsighted and Farsighted
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.
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2007
• 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
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clearly!
2007
Eye Fun 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 their 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
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2007