Ever ask why 20/20 is the standard for ''perfect'' eyesight and what it truly stands for? 20/20 vision is a phrase to express normal visual acuity or clarity of vision. In other words someone with such eyesight can clearly see an object at a distance of 20 feet that most people should be able to see from such a distance.
For those who don't have 20/20 vision, the number is assigned based on the first point at which they are able to see sharply, compared to what is normally expected. As an example, if your acuity is 20/100 that means that you have to be as close as 20 feet to see clearly what a person with normal vision would see at a distance of 100 feet.
A person who is assessed with 20/200 vision is considered blind, legally but can often achieve much improved vision by wearing prescription glasses or contact lenses or by undergoing laser eye surgery if they qualify.
Most eye doctors use a form of the Snellen eye chart, which was designed by Hermann Snellen, a Dutch eye doctor in the 1860's, to conduct a vision screening. While today there are many versions, the chart generally has 11 lines of uppercase letters which get smaller in size as one looks toward the bottom. The top of the chart usually shows the uppercase letter – ''E'' with letters being added gradually as you move down the chart. During the eye exam, the optometrist will examine which is the line with the smallest lettering you can make out. Every row is assigned a rating, with the 20/20 row usually being ascribed forth from the bottom. In cases in which the patient can't read, such as young children or handicapped individuals, the ''Tumbling E'' chart is employed. At the same scale as the traditional Snellen chart, the ''Tumbling E'' is composed of only the uppercase E in different rotations. The optometrist asks the patient to point to the right, left, top or bottom to show which direction the E is pointing. Both charts should be placed 20 feet away from where the patient is viewing it.
Despite common conception, 20/20 visual acuity does not show a person has flawless vision but rather that they see adequately at a distance. Complete vision includes many other necessary skills such as peripheral sight, depth perception, focus for near vision, color vision and coordination between the eyes amongst others.
While a vision screening with a Snellen chart can conclude whether you need a visual aid to see far away it will not give the optometrist a full perception of your total eye health. It's recommended that you still schedule an annual comprehensive eye exam to screen for potential diseases. Call our office now to schedule an eye exam in Crystal Lake, IL.