Ever question what 20/20 eyesight actually means? The phrase 20/20 vision describes a normal level of clarity of eyesight or visual acuity measured from a 20 feet distance. That is to say that an individual with 20/20 eyesight will be able to clearly see an object at a distance of 20 feet that the majority of people should be able to see from that distance.
For those who cannot see an object clearly at 20 feet away, the number is designated according to where they begin to see clearly in comparison to the norm. For instance, if your acuity is 20/100 that indicates that you have to be as close as 20 feet to see what a person with normal vision would be able to see at a distance of 100 feet.
It's also possible to have vision that is above the norm. For example a person that has 20/10 eyesight can see sharply at 20 feet what the average person can see only at 10 feet. Certain animals have more acute eyesight compared to man. For example, hawks have been known to have 20/2 eyesight, enabling them to identify prey from great heights.
Most eye care professionals use a version of the Snellen eye chart, created by Dutch eye doctor, Herman Snellen in the mid-1800's, to conduct an eye screening. While there are now quite a few variations, the chart generally has eleven rows with capital letters which get progressively smaller as one looks toward the bottom. The chart begins with the capital letter – ''E'' with the addition of more letters on the lines as they get smaller. During the vision screening, the eye doctor will look for the line with the smallest lettering you can see clearly. Each row is given a distance, with the 20/20 line typically being ascribed forth from the bottom. In cases where the patient isn't able to read, such as young children or handicapped individuals, an alternate version of the chart is used called the ''Tumbling E''. Similar to the standard Snellen chart, this version shows only the uppercase E in different spatial orientations. The patient uses their hand to show which direction the ''fingers'' of the E are pointing: right, left up or down. In order for the results to be accurate the chart must be placed 20 feet away from the patient's eyes.
Despite what many think, 20/20 eyesight does not show someone sees perfectly but only that they see adequately at a distance. ''Perfect'' eyesight includes a number of other important competencies such as peripheral sight, perception of depth, focus for near vision, color vision and coordination between the eyes to name a few.
While an eye exam with a Snellen chart can establish whether you need eyeglasses to improve distance vision it doesn't give the eye doctor a complete picture of the total health of your eyes and vision. Make sure you still go in for a yearly comprehensive eye exam which can diagnose potential conditions. Call our office today to book an eye exam in Tupelo, MS.