Have you ever asked yourself why 20/20 is the benchmark for ''perfect'' vision and what it actually means? The phrase 20/20 vision expresses a normal level of sharpness of vision or visual acuity calculated from 20 feet away from the object. That is to say that someone with such vision will be able to see an object clearly at a distance of 20 feet which is deemed the norm to see clearly from that distance.
For those who don't have 20/20 visual acuity, the number is determined according to where they begin to see clearly in comparison to the norm. For instance, if your vision is 20/100 that means that you have to be at a distance of 20 feet to see what someone with normal eyesight can see at a distance of 100 feet.
It's also possible to have better than 20/20 vision. For example someone with 20/10 vision can see sharply at 20 feet an object that most can see only at 10 feet. A number of animals have been known to have incredibly acute vision compared to the human species. A hawk for example can have 20/2 eyesight, enabling them to spot prey from great heights.
Most eye doctors employ a form of the Snellen eye chart, invented by Dutch eye doctor, Herman Snellen in the 1860's, to conduct a vision screening. While today there are quite a few versions, the chart generally has eleven rows with uppercase letters which get smaller in size as they move downward. The top of the chart usually shows the capital letter – ''E'' with letters being added subsequently as you look down the chart. During the vision test, the eye doctor will look for the smallest line of letters you can make out. Each line is given a rating, with the 20/20 line usually being ascribed forth from the bottom. For small 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 regular Snellen chart, the ''Tumbling E'' shows only the uppercase E in different spatial orientations. The eye doctor asks the patient to show which direction the arms of the E are facing.. Both charts needs to be placed at a distance of 20 feet from the patient's eyes.
Even though 20/20 vision does mean that the person's distance vision is average, this test on its own doesn't imply that a person has flawless eyesight. There are a number of other essential abilities needed that contribute to your overall vision such as side or peripheral vision, perception of depth, focus for near vision, color vision and coordination between the eyes to name a few.
While an eye exam with an eye chart will conclude whether you need eyeglasses to see clearly at a distance it will not give the optometrist a full perception of the complete health of your eyes and vision. It's recommended that you still schedule an annual comprehensive eye exam to screen for potential diseases. Contact our office now to book an eye exam in Cincinnati, OH.