Have you ever wondered why 20/20 is the standard for ''perfect'' eyesight and what it really represents? 20/20 vision is a phrase to describe normal visual acuity or clarity of vision. That is to say that someone with 20/20 vision will be able to see an object clearly at a distance of 20 feet that the majority of people should be able to see from that distance.
In cases of individuals that cannot see at 20/20, their visual acuity score is designated according to where they begin to see clearly in relation to what is normally expected. For instance, 20/100 vision means that you have to be at a distance of 20 feet to see what a person with normal eyesight can see at 100 feet away.
Someone who is assessed with 20/200 vision is considered legally blind however, they can often achieve much improved vision by using glasses or contacts or by undergoing LASIK if they qualify.
A typical eye screening is done with the use of a vision chart usually the familiar Snellen eye chart created by Dutch eye doctor, Herman Snellen in the 1860's. While there are now a number of versions, the chart usually has 11 lines with uppercase letters which get smaller in size as one looks downward. The top of the chart usually shows the uppercase letter - ''E'' with letters being added gradually as you look down the chart. During the vision test, the eye doctor will assess the line with the smallest lettering you can read. Each line is assigned a distance, with the 20/20 line usually being ascribed the eighth row. For small children, illiterate or handicapped persons who are not able to read or vocalize letters, a variation of the chart is used called the ''Tumbling E''. Similar to the standard Snellen chart, this version is composed of only the uppercase letter E in different directions. The optometrist asks the patient to mimic which direction the ''fingers'' of the E are facing.. Either chart needs to be positioned at a distance of 20 feet from the patient's eyes.
Even though 20/20 vision does show that the person's distance sight is normal, this test on its own does not suggest that the individual has flawless vision. There are a number of other essential abilities needed to make perfect vision such as side or peripheral sight, depth perception, focus for near vision, color vision and eye coordination amongst others.
While a vision screening with a Snellen chart will often determine if you need a visual aid to improve distance vision it will not give the eye doctor a full understanding of your complete eye and vision health. Make sure you still book an annual comprehensive eye exam to screen for any more serious conditions. Contact our office now to book a Overland Park, KS eye exam.