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 vision also known as visual acuity measured from 20 feet away from the object. In other words someone with such eyesight will be able to clearly see an object from 20 feet away that the majority of individuals are expected to be able to see from such a 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 sharply, in relation to what is normally expected. For example, 20/100 vision means that you must be at a distance of 20 feet to see clearly what someone with normal vision would be able to see at 100 feet away.
One can also have better than 20/20 vision. For instance someone with 20/10 vision can see sharply at 20 feet what the average person can only see at 10 feet distance. A number of animals have more acute eyesight compared to the human species. For example, hawks have been known to have 20/2 eyesight, enabling them to locate prey from high in the air.
An average vision test is done with the use of a vision chart such as the familiar Snellen eye chart created by Dutch eye doctor, Herman Snellen in the 1860's. While there are now a number of variations, the chart generally has 11 lines of capital letters which get smaller in size as they move downward. The chart begins with the uppercase letter – ''E'' and gradually adds more letters on the lines as they get smaller. During the eye exam, the eye doctor will assess the smallest line of letters you can read. Your score is determined since each line is given a distance, with the 20/20 line typically being ascribed the eighth row. In instances in which the patient can't read, such as young children or disabled persons, a variation of the chart is used called the ''Tumbling E''. Similar to the standard Snellen chart, this variation is composed of only the uppercase E in different spatial orientations. The eye doctor asks the patient to point to the right, left, top or bottom according to the direction the E is pointing. Either chart should be positioned at a distance of 20 feet from the patient's eyes.
Despite what many think, 20/20 eyesight doesn't indicate someone has flawless eyesight but only that their distance vision is normal. Total eyesight includes many other important abilities such as side or peripheral sight, perception of depth, focus for near vision, color vision and coordination between the eyes amongst others.
Although an eye exam with a Snellen chart can establish whether you require a visual aid to see clearly at a distance it will not give the eye doctor a comprehensive picture of your complete eye and vision health. It's recommended that you still schedule an annual comprehensive eye exam to screen for any more serious diseases. Contact our office today to schedule an eye exam in Plano, TX.