Ever ask why 20/20 is the benchmark for ''perfect'' eyesight and what it really represents? 20/20 vision is a phrase used to express normal visual acuity or clarity of vision. In other words someone with such visual acuity can clearly see an object from 20 feet away which is regarded as normal to see at that distance.
In cases of individuals that cannot see an object clearly at 20/20, the number is designated according to where they begin to see clearly compared to what is normally expected. As an example, 20/100 vision indicates that at 20 feet you can only see what someone with normal vision can see from 100 feet distance.
An individual with 20/200 vision is considered blind, legally but can often see normally by using glasses or contact lenses or by having laser eye surgery if they qualify.
Most optometrists employ some form of the Snellen eye chart, which was created by Dutch eye doctor, Herman Snellen in the 1860's, to conduct an eye exam. While today there are many versions, the chart typically has 11 rows of capital letters which get smaller in size as one looks downward. 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 read. Every row is assigned a distance, with the 20/20 row typically being ascribed the eighth row. In cases where the patient can't read, such as small children or disabled individuals, a different version of the chart is used called the ''Tumbling E''. Similar to the regular Snellen chart, this version shows only the uppercase E in different rotations. The patient uses their hand 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 the patient's eyes.
Despite what many think, 20/20 eyesight does not mean someone sees perfectly but rather that they are able to see normally at a distance. There are a number of other necessary abilities needed that contribute to your overall vision such as peripheral vision, perception of depth, focus for near vision, color vision and eye coordination to name a few.
It's important to remember that even though a vision screening using a Snellen chart can establish if you require a visual aid to see far away it doesn't give the eye doctor a complete understanding of your complete eye health. Make sure you still book an annual comprehensive eye exam to screen for vision-threatening diseases. Contact us today to schedule a Olathe, KS eye exam.