The Eye

As we look around us every day, the ability to see our world is something we may not think much about, until something goes wrong. About 120 million people in the U.S. wear eyeglasses or contact lenses to correct vision problems, according to the National Eye Institute (NEI). (Read about " Refractive Errors") Many others suffer from more serious problems and/or diseases that affect their ability to see, such as glaucoma, macular degeneration or cataracts. (Read about "Glaucoma" "Macular Degeneration" "Cataracts")

Eyesight is not something to take for granted. It depends on many different parts working together to form our vision. The basic parts of the eye, according to the American Optometric Association (AOA) include:

• eyelids - help protect the eye
• conjunctiva - this is what lines the eyelid
• cornea - the clear covering on the front of the eye
• sclera - the white of the eye
• iris - the colored part of the eye that helps control the amount of light that enters
• pupil - the hole in the center of the iris that is dark
• lens - focuses the light onto the back of the eye
• retina - the layer of nerves in the back of the eye, made up of rods and cones
• macula - a section of the retina near the center that lets us see fine details
• optic nerve - sends an electrical signal to the brain

How does all this work together? Light hits an object and bounces off. That reflected light enters the eye through the cornea. The cornea acts like a window and works with the lens to focus the light. The iris opens and closes, which adjusts the size of the pupil, to control how much light gets in. The light then hits the retina in the back of the eye, with its millions of light-sensing cells, the rods and cones. At this point, the light is changed into an electrical signal and sent through the optic nerve to the brain (Read about "The Brain" "Nervous System"), which converts that signal into an image it can understand. It works very much like a camera and film. The eye's cornea and lens are like the lens of a camera, which focus on an object. The retina is like the film where the image is laid down and the brain develops the picture.

One way you can help protect your eyesight is through regular eye exams. (Read about "Eye Exams") Another is by learning all you can about your eyes and the problems that can affect them. By following the links below, you can find more eye topics of interest.