Anatomy of the Eye

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.

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.

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 retinatakes 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.

Parts of the Eye

• 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.

• 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.

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.

Colorblindness

• Colorblind people have difficulty distinguishing between colors because of a malfunction of their cones.

• Some see only black and white.

• Some have difficulty determining red and green.

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.

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.

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.

• 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.

Standard Vision

• Perfect vision is considered to be 20/20.

• If you have 20/20 vision, you can see clearly at 20 feet what should normally be seen at that distance.

• If you have 20/100 vision, it means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet.

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.

• 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!

• 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

Eye Fun Facts