Have you ever asked yourself why 20/20 is the standard for ''perfect'' eyesight and what it truly represents? 20/20 vision is a term to describe a normal level of sharpness of eyesight (visual acuity) assessed at a distance of 20 feet. In other words someone with 20/20 visual acuity will be able to see an object clearly from 20 feet away which is deemed normal to see at that distance.
In cases of individuals that don't have 20/20 vision, their visual acuity score is designated according to the distance at which they are able to see sharply, in comparison to the norm. For example, 20/100 vision indicates that you have to be as close as 20 feet to see what someone with normal vision would be able to see at a distance of 100 feet.
You can also have vision that is above 20/20. For example someone with 20/10 eyesight can see clearly at 20 feet what the average person can see only at 10 feet. Certain animals have been known to have incredibly acute eyesight in comparison to man. A hawk for instance can have 20/2 eyesight, designed for locating prey from high in the air.
A typical eye screening is done by using a vision chart most commonly the familiar Snellen eye chart developed by Dutch eye doctor, Herman Snellen in the 1860's. While there are a number of versions, the chart usually has 11 lines of uppercase letters which get progressively smaller as one looks downward. The top of the chart usually shows the uppercase letter – ''E'' with the addition of more letters on the lines as they get smaller. During the vision screening, the eye doctor will assess the line with the smallest lettering you can see clearly. Every row is given a distance, with the 20/20 row usually being ascribed forth from the bottom. For small children, illiterate or disabled persons who can not read or vocalize letters, an alternate version of the chart is used called the ''Tumbling E''. Similar to the standard Snellen chart, this version 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. In order for the results to be accurate the chart needs to be placed 20 feet away from where the patient is viewing it.
Despite what many think, 20/20 eyesight does not show a person sees perfectly but only that their distance vision is normal. Complete eyesight involves a number of other necessary skills such as side or peripheral vision, depth perception, color vision, near vision and focusing and coordination between the eyes to name a few.
Although an eye exam with a Snellen chart will often establish whether you require eyeglasses to see far away it will not provide the eye doctor a complete understanding of your overall eye health. It's recommended that you still schedule a yearly comprehensive eye exam to screen for any more serious diseases. Contact us now to schedule a Lexington, KY eye exam.