Ever ask why 20/20 is the standard for ''perfect'' vision and what it truly represents? The term 20/20 vision describes normal visual acuity or clarity of vision. In other words someone with such visual acuity can see an object clearly from 20 feet away which is regarded as normal to see at that distance.
For those who don't have 20/20 vision, the number is determined according to the distance at which they are able to see clearly, in comparison to what is normally expected. For instance, 20/100 vision indicates that at 20 feet you can only see what someone with normal vision can see at 100 feet distance.
You can also have vision that is above 20/20. For example a person that has 20/10 eyesight can see sharply at 20 feet an object that the average person can only see at 10 feet distance. Members of the animal kingdom have been known to have incredibly acute eyesight compared to the human species. For example, hawks have been known to have 20/2 vision, enabling them to spot prey from great heights.
An average eye screening is done by using a vision chart usually the classic Snellen eye chart created by Hermann Snellen, a Dutch eye doctor in the 1860's. While there are quite a few versions, the chart usually shows eleven lines of uppercase letters which get smaller in size as one looks downward. The top of the chart usually shows one uppercase letter – ''E'' with letters being added gradually as you look down the chart. During the vision screening, the eye doctor will assess the smallest line of letters you can make out. Every row is assigned a rating, with the 20/20 line usually being ascribed forth from the bottom. In cases where the patient isn't able to read, such as small children or disabled persons, the ''Tumbling E'' chart is used. At the same scale as the regular Snellen chart, the ''Tumbling E'' portrays only the capital letter E in different rotations. The patient uses their hand to show which direction the ''fingers'' of the E are pointing: right, left top or bottom. In order for the results to be accurate the chart needs to be placed 20 feet away from the patient's eyes.
Despite common conception, 20/20 visual acuity doesn't show a person sees perfectly but only that they see well at a distance. Total eyesight involves a number of other necessary competencies such as peripheral vision, perception of depth, focus for near vision, color vision and coordination between the eyes amongst others.
It's important to remember that even though an eye exam using a Snellen chart can conclude whether you need glasses to see clearly at a distance it will not provide the optometrist a comprehensive picture of the total status of your eyes and vision. Make sure you still book a yearly comprehensive eye exam to screen for any more serious diseases. Contact our office today to book a Hoover, AL eye test.