Ever question why 20/20 is the benchmark for ''perfect'' eyesight and what it actually stands for? 20/20 vision is a phrase to express a normal level of clarity of vision also known as visual acuity determined from 20 feet away from the object. In other words someone with such vision will be able to clearly see an object at a distance of 20 feet which is deemed normal to see from that distance.
For those who don't have 20/20 visual acuity, the number is determined based on where they begin to see clearly compared to the norm. For example, 20/100 acuity indicates that you must be at a distance of 20 feet to see what someone with normal vision can see at a distance of 100 feet.
One can also have vision that is above 20/20. For instance a person that has 20/10 vision can see sharply at 20 feet what most can see only at 10 feet. Members of the animal kingdom have been known to have incredibly acute eyesight in comparison to what humans are capable of. A hawk for instance can have 20/2 vision, designed for locating prey from great heights.
A typical eye exam is done by using an eye chart usually the familiar Snellen eye chart designed by Dutch eye doctor, Herman Snellen in the mid-1800's. While today there are a number of variations, the chart generally has eleven lines with uppercase letters which get smaller in size as one looks downward. The chart begins with the capital letter – ''E'' with the addition of more letters on the lines as they get smaller. During the vision test, the eye doctor will examine which is the line with the smallest lettering you can see clearly. Each row is given a distance, with the 20/20 line usually being assigned the eighth row. For young children, illiterate or handicapped persons who can not read or vocalize letters, an alternate version of the chart is used called the ''Tumbling E''. At the same scale as the traditional Snellen chart, this version portrays only the uppercase E in different rotations. The optometrist asks the patient to point to the right, left, top or bottom based on the direction the E is 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 eyesight doesn't indicate someone has perfect vision but rather that they are able to see well from a distance. ''Perfect'' eyesight includes many other necessary skills such as side or peripheral vision, perception of depth, color vision, near vision and focusing and coordination between the eyes amongst others.
Although an eye exam with a Snellen chart can conclude if you need eyeglasses for better distance vision it will not give the eye doctor a comprehensive perception of the total status of your eyes and vision. You should still schedule an annual comprehensive eye exam to screen for vision-threatening diseases. Contact us now to book a Manchester, CT eye test.