Ever wonder why 20/20 is the standard for ''perfect'' vision and what it really stands for? The term 20/20 eyesight represents normal visual acuity or clarity of vision. In other words an individual with 20/20 eyesight can see an object clearly at a distance of 20 feet which is regarded as the norm to see at that distance.
For those who cannot see an object clearly at 20 feet away, the number is assigned based on where they begin to see clearly in relation to what is normally expected. For example, 20/100 acuity indicates that at a distance of 20 feet you can only see what someone with normal vision can see from 100 feet distance.
A person who is assessed with 20/200 visual acuity is considered blind, legally but can often see normally with the use of glasses or contact lenses or by having LASIK if they qualify.
Most eye doctors utilize some version of the Snellen eye chart, designed by Dutch eye doctor, Herman Snellen in the mid-1800's, to conduct a vision exam. While today there are quite a few variations, the chart generally has eleven rows of uppercase letters which get smaller in size as they move downward. The top of the chart usually shows the uppercase letter - ''E'' with letters being added subsequently as you move down the chart. During the vision screening, the eye doctor will look for the line with the smallest lettering you can read. Each line is given a distance, with the 20/20 line typically being assigned forth from the bottom. For small children, illiterate or handicapped persons who can not read or vocalize letters, the ''Tumbling E'' chart is used. Similar to the standard Snellen chart, the ''Tumbling E'' is composed of only the capital E in different directions. The person being tested uses their hand to point to the right, left, top or bottom to show which direction the E is pointing. Either chart should be positioned at a distance of 20 feet from the patient's eyes.
Although 20/20 eyesight does mean that the person is able to see as expected from a distance this metric alone doesn't show that the individual has perfect vision. There are a number of other necessary abilities needed that contribute to your overall vision such as side or peripheral sight, depth perception, focus for near vision, color vision and eye coordination amongst others.
While a vision screening using a Snellen chart can establish whether you require eyeglasses to see clearly at a distance it will not provide the optometrist a full picture of your total eye health. You should still schedule a yearly comprehensive eye exam which can identify potential diseases. Contact our office now to book a Mesa, AZ eye exam.