Have you ever asked yourself what 20/20 eyesight actually means? 20/20 vision is a phrase used to express normal visual acuity or clarity of vision. That is to say that someone with 20/20 vision can see an object clearly from 20 feet away that most individuals are expected to be able to see from that distance.
In cases of individuals that cannot see at 20/20, their visual acuity score is assigned according to the first point at which they are able to see clearly, compared to the norm. As an example, if your vision is 20/100 that means that at 20 feet you can only see an object that a person with normal vision can see at 100 feet away.
You can also have vision that is better than 20/20. For instance someone that has 20/10 eyesight can see sharply at 20 feet an object that the average person can only see at 10 feet. Certain animals have more acute eyesight in comparison to what humans are capable of. For example, hawks have been known to have 20/2 vision, enabling them to identify prey from great heights.
An average vision test is done with the use of an eye chart usually the classic Snellen eye chart created by Dutch eye doctor, Herman Snellen in the mid-1800's. While today there are a number of versions, the chart typically shows 11 lines with uppercase letters which get smaller in size as they move toward the bottom. The top of the chart usually shows the uppercase letter – ''E'' with the addition of more letters on the lines as they get smaller. During the vision test, the optometrist will examine which is the line with the smallest lettering you can see clearly. Each line is given a distance, with the 20/20 row usually being assigned the eighth row. In cases in which the patient can't read, such as small children or disabled persons, a different version of the chart is used called the ''Tumbling E''. Similar to the standard Snellen chart, this variation is composed of only the uppercase letter E in different directions. The eye doctor tells the patient to point to the right, left, top or bottom based on the direction the E is pointing. Both charts must be placed 20 feet away from where the patient is viewing it.
Although 20/20 eyesight does indicate that an individual is able to see at the norm from a distance this test alone does not suggest that the individual has flawless vision. There are many other necessary elements that contribute to your overall vision such as side or peripheral sight, depth perception, focus for near vision, color vision and coordination between the eyes amongst others.
Although an eye exam with an eye chart will often conclude if you need glasses to see clearly at a distance it doesn't give the optometrist a comprehensive picture of your complete eye and vision health. Make sure you still book an annual comprehensive eye exam which can identify potential conditions. Contact us now to book an eye exam in Centreville, VA.