Have you ever asked yourself why 20/20 is the standard for ”perfect” vision and what it really represents? 20/20 vision is a term used to describe a normal level of sharpness of eyesight also known as visual acuity measured from 20 feet away from the object. That is to say that someone with such vision can see an object clearly at a distance of 20 feet that the majority of individuals should be able to see from that distance.
In cases of individuals that don’t have 20/20 vision, the number is determined according to where they begin to see clearly in comparison to what is normally expected. For instance, if your acuity is 20/100 that indicates that at 20 feet you can only see what the baseline would see from 100 feet .
Someone who is assessed with 20/200 visual acuity is considered blind, legally however, they can often achieve much improved vision through prescription glasses or contacts or by undergoing LASIK if they are eligible.
Most eye doctors utilize some form of the Snellen eye chart, designed by Hermann Snellen, a Dutch eye doctor in the mid-1800’s, to perform an eye screening. While today there are many versions, the chart typically has eleven lines of uppercase letters which get progressively smaller as they move downward. The top of the chart usually shows the uppercase letter – ”E” and subsequently includes more letters as they get smaller. During the vision test, the eye doctor will look for the line with the smallest lettering you can make out. Your score is determined since each row is assigned a distance, with the 20/20 row 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 used. Similar to the regular Snellen chart, the ”Tumbling E” portrays only the uppercase letter E in different spatial orientations. The optometrist tells the person being tested to point to the right, left, top or bottom based on the direction the E is pointing. Either chart must be placed at a distance of 20 feet from where the patient is viewing it.
Despite common perception, 20/20 eyesight does not indicate an individual has flawless eyesight but merely that they see as expected at a distance. Complete eyesight includes many other necessary abilities such as peripheral vision, depth perception, color vision, near vision and focusing and coordination between the eyes amongst others.
While a vision screening using an eye chart will conclude if you need glasses to see clearly at a distance it will not provide the optometrist a comprehensive perception of your complete eye and vision health. You should still book a yearly comprehensive eye exam which can diagnose vision-threatening conditions. Contact our office now to schedule an eye exam in Scottsdale, AZ.