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Alpharetta, GA Vision Tests: What 20/20 Vision Actually Means


Have you ever asked yourself what 20/20 eyesight actually stands for? 20/20 vision is a phrase to describe normal visual acuity or clarity of vision. In other words an individual with such visual acuity will be able to see an object clearly at a distance of 20 feet that most people should be able to see from that distance.

For those who cannot see an object clearly at 20/20, their visual acuity score is designated based on the distance at which they are able to see clearly, compared to the norm. As an example, 20/100 vision means that at 20 feet you can only see an object that the baseline would see at 100 feet distance.

It's also possible to have vision that is better than the norm. For instance a person that has 20/10 vision can see clearly at 20 feet an object that the average person can only see at 10 feet distance. Members of the animal kingdom particularly birds of prey have been known to have incredibly acute eyesight in comparison to what humans are capable of. A hawk for example can have 20/2 vision, enabling them to locate prey from high in the air.

Most eye doctors employ a form of the Snellen eye chart, invented by Dutch eye doctor, Herman Snellen in the 1860's, to conduct an eye exam. While there are quite a few versions, the chart typically has eleven rows with capital letters which get progressively smaller as one looks toward the bottom. The chart begins with one capital letter – ''E'' with letters being added gradually as you move down the chart. During the eye exam, the eye doctor will examine which is the line with the smallest lettering you can make out. Every line is given a distance, with the 20/20 row usually being assigned forth from the bottom. For small children, illiterate or disabled persons who can not read or vocalize letters, the ''Tumbling E'' chart is employed. At the same scale as the standard Snellen chart, this variation shows only the capital letter E in different rotations. The patient uses their hand to point to the right, left, top or bottom to show which direction the E is facing. Both charts must be placed at a distance of 20 feet from where the patient is viewing it.

Despite what many think, 20/20 visual acuity doesn't show someone has flawless vision but only that they are able to see normally from a distance. There are many other essential elements that contribute to your overall vision such as peripheral sight, perception of depth, color vision, near vision and focusing and coordination between the eyes amongst others.

Although an eye exam with an eye chart can determine whether you require a visual aid to correct for distance vision it will not provide the eye doctor a full perception of the overall health of your eyes and vision. Make sure you still go in for a yearly comprehensive eye exam to screen for vision-threatening conditions. Contact our office today to book an eye exam in Alpharetta, GA.