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Vision Test 20 20



 Submitted by Medical Health Test Team on June 30, 2010
20 20 Vision Testing

A human being is able to see things thanks to the proper functioning of the optical system. The optic system is made up of the eyes, the optic nerves and the brain, which computes the information received from the optic nerves. Each human eye has a lens which is used to project the image to the rear wall of the eye. The projected image is then transmitted in the form of an electrical impulse to the brain where it is processed.

Many human beings require glasses to be able to view objects or images properly. These glasses are usually calibrated for long distance viewing or short distance viewing. Glasses are used when there is an abnormality with the focus of the lens in the eye. When the focus goes awry, the lens projects an abnormal image to the back of the eye. This image is out of focus and therefore difficult to make out. People with long distance vision problems will be able to see items nearby easily and the opposite is true of people with short distance vision problems.

The rating of a person’s eyes is based on a vision chart test. The vision chart is a series of lines on which alphabets are printed. Each line represents a different level of vision. During a vision test, the subject is asked to read each line until the subsequent line cannot be read. When this limit is reached, one can use the limit to assess the subject’s vision.

The term 20/20 vision is used to describe perfect vision in an individual. 20/20 vision means that the individual is able to clearly see items that are twenty feet away from a distance of twenty feet. If the same fraction is 20/40, then the individual would need to be at 20 feet distance to read a line that a normal eye would be able to read from 40 feet away. This progression is used to explain the subject’s rate of vision deterioration. In many such tests, dummy eyeglasses are used to correct the vision. These eyeglasses allow different lenses to be inserted with different rates of focal correction. With each subsequent lens, the subject is asked to attempt reading again until the subject is able to clearly read the 20/20 line. When this happens, the quantity of correction is noted and the prescription for that level of correction in eye glasses is made.

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