Have you ever asked yourself why 20/20 is the benchmark for ''perfect'' vision and what it really means? The phrase 20/20 eyesight expresses a normal level of clarity of vision also known as visual acuity measured from a 20 feet distance. In other words someone with 20/20 vision can see an object clearly from 20 feet away which is deemed the norm to see at that distance.
For those who cannot see an object clearly at 20/20, the number is determined according to the distance at which they are able to see sharply, in comparison to what is normally expected. As an example, 20/100 acuity indicates that you have to be as close as 20 feet to see clearly what someone with normal vision can see at 100 feet away.
An individual with 20/200 visual acuity is considered legally blind but can often see normally with the use of glasses or contacts or by undergoing laser eye surgery if they qualify.
An average eye exam is done with the use of an eye chart usually the classic Snellen eye chart designed by Dutch eye doctor, Herman Snellen in the 1860's. While today there are many variations, the chart generally shows 11 rows with capital letters which get smaller in size as they move toward the bottom. The chart begins with one uppercase letter – ''E'' with letters being added subsequently as you look down the chart. During the eye exam, the eye doctor will assess the smallest line of letters you can make out. Your score is determined since each line is assigned a distance, with the 20/20 row typically being assigned the eighth row. In instances in which the patient isn't able to read, such as small children or handicapped persons, a varied version of the chart is used called the ''Tumbling E''. At the same scale as the regular Snellen chart, this variation shows only the capital E in different rotations. The eye doctor tells the patient to show which direction the arms of the E are facing: right, left top or bottom. In order for the results to be accurate the chart should be placed 20 feet away from where the patient is viewing it.
Despite common perception, 20/20 vision does not indicate a person sees perfectly but rather that they are able to see well at a distance. There are a number of other necessary elements that contribute to your overall vision such as side or peripheral vision, depth perception, focus for near vision, color vision and coordination between the eyes to name a few.
While a vision screening using an eye chart will often determine whether you need a visual aid to see far away it doesn't provide the eye doctor a full picture of the overall health of your eyes and vision. It's recommended that you still go in for a yearly comprehensive eye exam to screen for potential conditions. Contact us today to schedule a Duluth, MN eye exam.