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Vision 101

By Troy Bedinghaus, O.D., About.com

Updated: March 23, 2009

About.com Health's Disease and Condition content is reviewed by the Medical Review Board

Our eyes are very complex organs. In order for our eyes to see, there must be light. Light rays reflect off of an object and enter the eye through the cornea. At the back of the eye the light is focused by the retina, then it is converted into electric signals to be sent to the brain. Once the brain receives the signals, vision occurs. If the eye cannot properly focus an image it is said to have a refractive error. An eye doctor can determine the type of refractive error by a test called a refraction. Correcting a refractive error is achieved by glasses, contacts or refractive surgery. This is Vision 101.

Visual Acuity and Refractive Errors:

Visual acuity is a measure of the clarity and sharpness of your vision. Measuring your visual acuity is a quick method for a health care professional to discover vision problems. Normal visual acuity is usually expressed as 20/20 and indicates the smallest detail a person should be able to see at a standard testing distance of 20 feet. Visual acuity test results help health care professionals determine if you may be nearsighted, farsighted or have astigmatism.

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