Have you ever asked yourself why 20/20 is the standard for ''perfect'' eyesight and what it truly represents? 20/20 vision is a term used to express a normal level of sharpness of vision (visual acuity) assessed from a 20 feet distance. In other words an individual with 20/20 vision can see an object clearly from 20 feet away which is deemed normal to see from that distance.
In cases of individuals that cannot see an object clearly at 20/20, their visual acuity score is assigned according to where they begin to see clearly in relation to the norm. For example, if your vision is 20/100 that means that at a distance of 20 feet you can only see an object that the baseline would see at 100 feet distance.
It's also possible to have vision that is above the norm. For instance a person that has 20/10 eyesight can see sharply at 20 feet an object that the average person can see only at 10 feet. Members of the animal kingdom particularly birds of prey have more acute vision in comparison to what humans are capable of. A hawk for example can have 20/2 eyesight, enabling them to spot prey from high in the air.
Most eye care professionals utilize some version of the Snellen eye chart, which was created by Dutch eye doctor, Herman Snellen in the 1860's, to conduct a vision exam. While there are now many versions, the chart generally has 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 letters being added subsequently as you move down the chart. During the eye exam, the eye doctor will examine which is the line with the smallest lettering you can read. Each line is given a rating, with the 20/20 row typically being ascribed the eighth row. For young children, illiterate or disabled 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, the ''Tumbling E'' is composed of only the uppercase E in different spatial orientations. The eye doctor asks the person being tested to point to the right, left, top or bottom based on the direction the E is pointing. In order for the results to be accurate the chart should be placed at a distance of 20 feet from the patient's eyes.
Despite common conception, 20/20 vision does not mean someone has perfect vision but merely that their distance vision is normal. There are a number of other essential elements to make perfect vision such as side or peripheral vision, depth perception, color vision, near vision and focusing and eye coordination amongst others.
Although a vision screening with an eye chart will establish if you need a visual aid to improve distance vision it will not give the eye doctor a comprehensive picture of your total eye health. It's recommended that you still book an annual comprehensive eye exam which can diagnose any more serious diseases. Contact our office now to schedule a West Winfield, NY eye test.