Have you ever wondered why 20/20 is the standard for ''perfect'' vision and what it really stands for? 20/20 vision is a phrase used to describe normal visual acuity or sharpness of vision. That is to say that an individual with 20/20 visual acuity will be able to clearly see an object from 20 feet away that most individuals should be able to see from that distance.
In cases of individuals that don't have 20/20 vision, their visual acuity score is determined based on where they begin to see clearly compared to what is normally expected. As an example, 20/100 acuity indicates that you must be as close as 20 feet to see what a person with normal visual acuity can see at 100 feet away.
Someone whose vision is 20/200 or below is considered blind, legally however, they can often see normally by wearing prescription glasses or contacts or by having LASIK if they qualify.
Most eye doctors use some version of the Snellen eye chart, developed by Hermann Snellen, a Dutch eye doctor in the mid-1800's, to perform a vision screening. While today there are many versions, the chart typically has eleven lines of uppercase letters which get smaller in size as one looks downward. The chart begins with one uppercase letter – ''E'' with letters being added gradually as you move down the chart. During the vision test, the eye doctor will look for the smallest line of letters you can read. Every row is given a distance, with the 20/20 line typically being assigned forth from the bottom. In instances where the patient can't read, such as small children or handicapped persons, a variation of the chart is used called the ''Tumbling E''. Similar to the traditional Snellen chart, this variation portrays only the uppercase E in different spatial orientations. The optometrist tells the patient to show which direction the arms of the E are pointing.. In order for the results to be accurate the chart must be placed at a distance of 20 feet from the patient's eyes.
Despite what many think, 20/20 visual acuity does not indicate a person sees perfectly but merely that they see normally from a distance. Complete eyesight involves a number of other important skills such as peripheral sight, perception of depth, color vision, near vision and focusing and eye coordination amongst others.
Although a vision screening with an eye chart will determine whether you need glasses to see clearly at a distance it will not give the optometrist a full understanding of the complete status of your eyes and vision. It's recommended that you still book a yearly comprehensive eye exam which can identify any more serious conditions. Call us now to schedule a Saginaw, MI eye exam.