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Philadelphia, PA Eye Exams: What Does 20/20 Eyesight Really Mean?


Ever question what 20/20 eyesight really represents? The term 20/20 eyesight expresses normal visual acuity or clarity of vision. That is to say that an individual with 20/20 vision will be able to see an object clearly at a distance of 20 feet that most individuals are expected to be able to see from such a distance.

For those who cannot see an object clearly at 20/20, their visual acuity score is assigned based on the distance at which they are able to see sharply, in relation to what is normally expected. For example, 20/100 vision means that at a distance of 20 feet you can only see an object that someone with normal vision can see from 100 feet .

One can also have vision that is above the norm. For instance a person with 20/10 vision can see sharply at 20 feet an object that the average person can only see at 10 feet. Members of the animal kingdom particularly birds of prey have been known to have incredibly acute vision in comparison to humans. For example, hawks have been known to have 20/2 vision, designed for spotting prey from great heights.

An average eye test is done with the use of a vision chart such as the familiar Snellen eye chart created by Dutch eye doctor, Herman Snellen in the 1860's. While there are many variations, the chart generally shows eleven rows with capital letters which get smaller in size as they move downward. The chart begins with one uppercase letter - ''E'' with letters being added subsequently as you move down the chart. During the eye exam, the optometrist will examine which is the line with the smallest lettering you can read. Every row is assigned a distance, with the 20/20 line usually being assigned forth from the bottom. For young children, illiterate or disabled persons who are not able to read or vocalize letters, the ''Tumbling E'' chart is employed. Similar to the standard Snellen chart, this version is composed of only the uppercase E in different directions. The eye doctor asks the patient to show the direction the ''fingers'' of the E are facing: right, left top or bottom. Either chart should be placed 20 feet away from the patient's eyes.

Despite common perception, 20/20 visual acuity does not show an individual has flawless eyesight but merely that their distance vision is normal. There are a number of other necessary elements to make perfect vision such as peripheral sight, depth perception, color vision, near vision and focusing and eye coordination to name a few.

Although a vision screening with an eye chart will often determine whether you require eyeglasses to see far away it will not provide the optometrist a full perception of the total health of your eyes and vision. Make sure you still go in for an annual comprehensive eye exam to screen for potential diseases. Call our office now to book an eye exam in Philadelphia, PA.