Ever wonder why 20/20 is the standard for ''perfect'' eyesight and what it actually means? The term 20/20 eyesight expresses a normal level of clarity of eyesight (visual acuity) measured from a 20 feet distance. In other words an individual with 20/20 visual acuity can clearly see an object from 20 feet away that the majority of individuals should be able to see from such a distance.
For those who don't have 20/20 vision, their visual acuity score is designated according to where they begin to see clearly in comparison to what is normally expected. For instance, if your acuity is 20/100 that means that at 20 feet you can only see an object that someone with normal vision can see from 100 feet .
A person with 20/200 vision is considered legally blind but can often achieve much improved eyesight by wearing prescription glasses or contacts or by having laser eye surgery if they qualify.
Most eye care professionals employ some version of the Snellen eye chart, designed by Hermann Snellen, a Dutch eye doctor in the 1860's, to perform a vision test. While today there are a number of variations, the chart typically shows eleven rows of uppercase letters which get progressively smaller as one looks toward the bottom. 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 assess the line with the smallest lettering you can see clearly. Every row is assigned a rating, with the 20/20 row typically being assigned the eighth row. For young children, illiterate or handicapped persons who can not read or vocalize letters, the ''Tumbling E'' chart is used. At the same scale as the traditional Snellen chart, this variation is composed of only the uppercase E in different directions. The patient uses their hand to show which direction the arms of the E are pointing: right, left up or down. In order for the results to be accurate the chart should be positioned at a distance of 20 feet from where the patient is viewing it.
Despite what many think, 20/20 visual acuity does not indicate an individual sees perfectly but merely that they are able to see as expected at a distance. There are a number of other essential elements to make perfect vision such as side or peripheral sight, perception of depth, focus for near vision, color vision and eye coordination to name a few.
Although an eye exam with a Snellen chart will establish whether you need eyeglasses to see clearly at a distance it doesn't provide the optometrist a comprehensive picture of the complete status of your eyes and vision. It's recommended that you still book a yearly comprehensive eye exam which can diagnose any more serious conditions. Contact our office today to schedule a Manasquan, NJ eye exam.