Have you ever wondered what 20/20 eyesight actually represents? 20/20 vision is a term to describe normal visual acuity or clarity of vision. That is to say that an individual with such eyesight can see an object clearly from 20 feet away that the majority of individuals should be able to see from such a distance.
In cases of individuals that don't have 20/20 visual acuity, their visual acuity score is determined according to the distance at which they are able to see clearly, in comparison to the norm. As an example, 20/100 acuity means that you must be at a distance of 20 feet to see clearly what someone with normal eyesight would be able to see at 100 feet away.
An individual who is assessed with 20/200 vision is considered blind, legally but can often achieve much improved vision by wearing glasses or contact lenses or by having laser eye surgery if they qualify.
Most eye doctors employ a form of the Snellen eye chart, which was developed by Hermann Snellen, a Dutch eye doctor in the mid-1800's, to perform an eye exam. While today there are quite a few versions, the chart typically has eleven lines with uppercase letters which get smaller in size as they move toward the bottom. The chart begins with the uppercase letter – ''E'' with letters being added gradually as you look down the chart. During the vision screening, the optometrist will assess the line with the smallest lettering you can make out. Every row is given a rating, with the 20/20 line typically being ascribed forth from the bottom. In instances in which the patient can't read, such as young children or disabled individuals, the ''Tumbling E'' chart is employed. At the same scale as the regular Snellen chart, this version portrays only the uppercase letter E in different rotations. The eye doctor tells the person being tested to show the direction the arms of the E are pointing.. Both charts needs to be placed at a distance of 20 feet from where the patient is viewing it.
While 20/20 eyesight does mean that the person's distance vision is good, this measure on its own does not mean that someone has flawless vision. There are many other necessary abilities needed to make perfect vision such as side or peripheral vision, depth perception, focus for near vision, color vision and eye coordination amongst others.
While a vision screening using a Snellen chart can conclude whether you need glasses to see far away it will not give the eye doctor a complete picture of the complete status of your eyes and vision. You should still schedule a yearly comprehensive eye exam to screen for vision-threatening conditions. Contact us today to book a Baltimore, MD eye exam.