Philadelphia, PA Vision Tests: What 20/20 Vision Really Means


Ever question what 20/20 eyesight actually stands for? 20/20 vision is a phrase to describe a normal level of clarity of eyesight (visual acuity) assessed from a 20 feet distance. That is to say that someone with such eyesight can see an object clearly from 20 feet away that the majority of individuals are expected to be able to see from such a distance.

For those who cannot see at 20/20, the number is designated according to the first point at which they are able to see clearly, in comparison to the norm. For example, 20/100 vision means that you have to be at a distance of 20 feet to see what someone with normal vision would see at a distance of 100 feet.

An individual with 20/200 eyesight is considered legally blind but can often see normally through glasses or contacts or by having laser eye surgery if they qualify.

Most eye doctors utilize some version of the Snellen eye chart, developed by Dutch eye doctor, Herman Snellen in the mid-1800's, to perform an eye test. While there are now a number of versions, the chart generally has eleven lines of capital letters which get progressively smaller as they move toward the bottom. The top of the chart usually shows the uppercase letter – ''E'' with the addition of more letters as they get smaller. During the eye exam, the eye doctor will look for the smallest line of letters you can make out. Your score is determined since each line is given a distance, with the 20/20 line typically being ascribed forth from the bottom. For small children, illiterate or handicapped persons who can not read or vocalize letters, a different version of the chart is used called the ''Tumbling E''. At the same scale as the standard Snellen chart, this variation portrays only the uppercase letter E in different directions. The person being tested uses their hand to point to the right, left, top or bottom according to the direction the E is pointing. Either chart must be positioned at a distance of 20 feet from the patient's eyes.

Despite common perception, 20/20 visual acuity does not mean an individual sees perfectly but rather that they see as expected at a distance. There are a number of other essential abilities needed to make perfect vision such as side or peripheral vision, depth perception, focus for near vision, color vision and coordination between the eyes amongst others.

While an eye exam with an eye chart can establish if you need a visual aid to see far away it doesn't give the eye doctor a full understanding of the complete health of your eyes and vision. You should still schedule a yearly comprehensive eye exam which can diagnose potential diseases. Call our office now to schedule a Philadelphia, PA eye exam.

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