Have you ever asked yourself why 20/20 is the benchmark for ''perfect'' vision and what it actually stands for? The phrase 20/20 vision represents a normal level of sharpness of eyesight (visual acuity) calculated from a 20 feet distance. In other words someone with 20/20 eyesight can see an object clearly at a distance of 20 feet that most people should be able to see from that distance.
For those who cannot see an object clearly at 20/20, the number is assigned according to where they begin to see clearly in relation to what is normally expected. As an example, if your vision is 20/100 that indicates that you must be at a distance of 20 feet to see clearly what someone with normal vision can see at a distance of 100 feet.
A person whose eyesight is 20/200 or below is considered blind, legally however, they can often achieve much improved eyesight by wearing prescription glasses or contact lenses or by having laser eye surgery if they are eligible.
A typical eye test is done by using an eye chart such as the familiar Snellen eye chart invented by Dutch eye doctor, Herman Snellen in the mid-1800's. While there are now quite a few variations, the chart typically shows eleven lines with uppercase letters which get smaller in size as one looks toward the bottom. The top of the chart usually shows one capital letter - ''E'' and subsequently includes more letters on the lines as they get smaller. During the eye exam, the optometrist will examine which is the line with the smallest lettering you can see clearly. Your score is determined since each row is assigned a distance, with the 20/20 line typically being assigned the eighth row. For young children, illiterate or disabled persons who can not read or vocalize letters, the ''Tumbling E'' chart is employed. At the same scale as the traditional Snellen chart, this variation is composed of only the uppercase letter E in different directions. The person being tested uses their hand to point to the right, left, top or bottom to show which direction the E is pointing. Either chart should be placed 20 feet away from where the patient is viewing it.
Although 20/20 vision does indicate that the person's distance sight is average, this test alone does not show that someone has flawless vision. There are many other essential 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 a vision screening using a Snellen chart can conclude if you need glasses to see clearly at a distance it will not provide the eye doctor a comprehensive understanding of your complete eye health. It's recommended that you still schedule a yearly comprehensive eye exam to screen for vision-threatening diseases. Call us today to schedule an eye exam in Mill Creek, WA.