Ever ask what 20/20 vision really stands for? The term 20/20 eyesight represents a normal level of clarity of vision also known as visual acuity calculated from a 20 feet distance. In other words an individual with 20/20 visual acuity can see an object clearly at a distance of 20 feet that the majority of people should be able to see from such a distance.
For those who don't have 20/20 visual acuity, the number is designated based on where they begin to see clearly in comparison to the norm. As an example, 20/100 acuity indicates that at a distance of 20 feet you can only see an object that the baseline would see at 100 feet .
You can also have vision that is better than 20/20. For instance someone with 20/10 vision can see clearly at 20 feet an object that the average person can see only at 10 feet. Certain animals have been known to have incredibly acute eyesight in comparison to what humans are capable of. For example, hawks have been known to have 20/2 eyesight, enabling them to spot prey from great heights.
Most eye care professionals utilize some version of the Snellen eye chart, designed by Hermann Snellen, a Dutch eye doctor in the mid-1800's, to perform a vision test. While there are quite a few variations, the chart generally has 11 rows of capital letters which get smaller in size as they move toward the bottom. The top of the chart usually shows the uppercase letter – ''E'' with letters being added gradually as you look down the chart. During the vision test, the optometrist will determine which is the line with the smallest lettering you can make out. Each row is given a rating, with the 20/20 line typically being assigned the eighth row. In cases in which the patient can't read, such as small children or disabled persons, the ''Tumbling E'' chart is employed. Similar to the regular Snellen chart, this version shows only the capital letter E in different directions. The patient uses their hand to indicate the rotational direction the arms of the E are pointing.. Either chart needs to be positioned 20 feet away from the patient's eyes.
Despite what many think, 20/20 visual acuity does not indicate an individual has flawless eyesight but only that their distance vision is normal. ''Perfect'' vision includes many other necessary skills such as side or peripheral sight, perception of depth, focus for near vision, color vision and eye coordination to name a few.
Although an eye exam using an eye chart can establish if you require a visual aid to see far away it will not give the eye doctor a complete perception of your complete eye and vision health. You should still schedule a yearly comprehensive eye exam to screen for potential diseases. Contact us today to schedule an eye exam with our Memphis optometrist.