The perception of vision is a process involving the optic system. An object or image is visible because of the way in which it reflects or projects light. This light enters the lens of the eye and is projected onto the inner surface of the eye. Here, the image is converted into an electrical signal which is sent to the brain through the optic nerves. The brain is responsible for processing the image which is what controls our perception of any visual stimulus.
Many human beings suffer from vision related problems. These problems occur when the lens of the eye loses its focus. This loss of focus causes the image that is perceived to be blurred. The use of eye glasses is required to correct the angle of the rays of light entering the eye so that the new focal length (caused by the change in the lens) is compensated for. The use of eye glasses allows the vision to be restored to normal.
In order to test an individual’s quality of eyesight, a vision test chart is used. Modern test procedures use a computer based imaging process to test the eye. However, many people still use the traditional vision test chart which is simple and easy to use. It is also extremely quick and could be used to make a relatively accurate diagnosis of a person’s quality of eyesight.
The test chart is on a white background. Several lines of alphabets are printed on this white background. Each successive line is a few sizes smaller than the line above it. Many charts also use a green and red band on the white background.
Each level of text size represents a level of vision. Some people have focal problems which affect their long distance vision while others have focal problems which affect their short distance vision. The ability to perceive only the larger alphabets is associated with long distance vision problems. An increased ability to view even the smallest line of letters is associated with a short term problem.
During a vision chart test, the patient may be made to view the chart with different corrective lenses being applied to check which level of correction allows them perfect vision. This is used to diagnose the severity of their focal problem and allows a prescription of eye glasses to be made. When conducted correctly from the right distance, a vision chart test could be completely accurate.