Take a Look at the Eye

Your eyes are at work from the moment you wake up to the moment you close them to go to sleep. They take in tons of information about the world around you, then they process the information and transfer it to your brain.

The eye is about 1 inch around, and it sits right behind the eyelid. It sits in a little hollow area (the eye socket) in the skull, and it s protected by the eyelid. The eyelid opens and shuts several times a minute; it s an involuntary action known as blinking. Blinking allows the eyelid to keep the eye clean. The eyelid also has great reflexes that protect the eye in different situations. When you step into bright light, the eyelids involuntarily squeeze together tightly to protect the eyes.

The white part of the eyeball is called the sclera. Look very closely at the white of the eye, and you ll see blood vessels that bring blood to the eye. The next layer on the eye is the cornea. The cornea is barely visible because it s made of clear tissue. The cornea helps the eye focus.

Behind the cornea are the iris and the pupil. The iris is the colorful part of the eye. The iris has muscles that adjust to control how much light goes through the pupil. The pupil is the black circular hole in the center of the iris, and it lets light enter the eye. Between the iris and cornea is the anterior that gives the eye oxygen, protein, and glucose.

After light enters the pupil, it hits the lens. The lens sits behind the iris, and it s clear and colorless. The lens job is to focus light rays onto the back of the eyeball (called the retina). The lens is suspended in the eye by a bunch of fibers attached to a muscle called the ciliary muscle. The ciliary muscle has the amazing job of changing the shape of the lens. When you look at things up close, the lens becomes thicker to focus the correct image onto the retina. When you look at things far away, the lens becomes thinner.

The biggest part of the eye is behind the lens, the vitreous body. It s filled with a clear material called the vitreous humor. After light passes through the lens, it shines straight through the vitreous humor to the back of the eye.

Past the vitreous body, is the retina ( The retina is tiny but it s full of millions of cells that are sensitive to light. It receives blood from the retinal vessels in order to allow it to function correctly. The retina takes the light that it receives through the cornea, pupil, and lens, and changes it into nerve signals that the brain can understand. It processes the light with special cells called rods and cones. Rods are the ones working to check out the shape of your friend and how he s moving. Cones are a little different because they sense color. Cones need more light than rods do for them to work well - this explains why it s hard to see different colors in the dark. Sometimes the cornea, lens, and retina don t work perfectly as a team, and the image ends up at the wrong place at the back of the eye. Sometimes the image appears in front or in back of the retina, instead of right on it. When this happens it just means that a person needs glasses to help focus the image correctly on the retina.

After the retina changes the colors and shapes into nerve signals, the signals go to the optic nerve. The optic nerve comes out of the back of the eye. When light passes through the lens and the image hits the retina, the image is upside-down. So the message that the optic nerve brings to the brain is upside-down. So your brain flips the image over so it s right-side up.

The eye has its own special cleaning system. Above the outer corner of each eye are the lacrimal glands, and they make tears. Every time you blink your eye, a tiny bit of tear fluid comes out of your upper eyelid. It washes away any germs, dust, or other particles that don t belong in your eye. It also keeps your eye from drying out. Then the fluid drains out of your eye by going into the lacrimal duct (this is also called the tear duct). You can see the opening of your tear duct if you very gently pull down the inside corner of your eye. Sometimes your eye needs to make even more tear fluid than it normally does. If you ve ever been poked in the eye by mistake or been in a dusty or smoky area, your eyes may have worked double time to protect themselves by making lots of tears. These tears helped to keep your eyes from becoming injured or dried out.

Eyes do everything from letting light in to figuring out colors to sending information to the brain. They protect themselves from light that s too bright, and they even have a great way of keeping clean. Protect your eyes by wearing goggles when you re taking classes like wood or metal shop, art, or science lab. And treat your eyes right by wearing sunglasses when you re out in the bright sun. Too much light can damage your lenses and retinas and affect your eyesight.