Have you ever asked yourself what 20/20 eyesight really stands for? 20/20 vision is a phrase used to express a normal level of clarity of eyesight or visual acuity determined from 20 feet away from the object. That is to say that an individual with such visual acuity will be able to see an object clearly at a distance of 20 feet that most people should be able to see from that distance.
For those who cannot see an object clearly at 20/20, the number is determined based on the first point at which they are able to see clearly, in relation to what is normally expected. As an example, if your acuity is 20/100 that indicates that you must be as close as 20 feet to see what a person with normal visual acuity would be able to see at 100 feet away.
An individual who is assessed with 20/200 visual acuity is considered blind, legally but can often see normally by using glasses or contact lenses or by undergoing LASIK if they qualify.
Most optometrists employ some form of the Snellen eye chart, designed by Hermann Snellen, a Dutch eye doctor in the mid-1800's, to conduct a vision test. While there are now many versions, the chart usually has 11 lines with capital 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 assess the line with the smallest lettering you can make out. Your score is determined since each line is assigned a rating, with the 20/20 line usually being assigned forth from the bottom. In cases where the patient isn't able to read, such as young children or handicapped persons, an alternate version of the chart is used called the ''Tumbling E''. Similar to the standard Snellen chart, the ''Tumbling E'' shows only the uppercase E in different spatial orientations. The person being tested uses their hand to mimic the rotational direction the ''fingers'' of the E are facing.. In order for the results to be accurate the chart needs to be positioned 20 feet away from where the patient is viewing it.
Despite what many think, 20/20 eyesight does not show a person has flawless vision but merely that their distance vision is normal. There are a number of other essential abilities needed that contribute to your overall vision such as side or peripheral vision, depth perception, color vision, near vision and focusing and coordination between the eyes amongst others.
While an eye exam using an eye chart will often conclude if you need glasses to see far away it will not give the eye doctor a comprehensive perception of your overall eye and vision health. It's recommended that you still schedule a yearly comprehensive eye exam which can identify vision-threatening diseases. Contact us now to schedule a Knoxville, TN eye test.