Have you ever wondered why 20/20 is the benchmark for ''perfect'' eyesight and what it truly represents? 20/20 vision is a phrase to express normal visual acuity or clarity of vision. In other words someone with 20/20 vision can clearly see an object at a distance of 20 feet that the majority of people are expected to be able to see from such a distance.
For those who cannot see an object clearly at 20/20, their visual acuity score is determined based on the first point at which they are able to see clearly, in comparison to what is normally expected. As an example, 20/100 vision means that at 20 feet you can only see an object that someone with normal vision can see at 100 feet .
An individual can also have better than 20/20 vision. For instance someone with 20/10 eyesight can see sharply at 20 feet what the average person can see only at 10 feet. A number of animals particularly birds of prey have been known to have incredibly acute eyesight compared to man. For example, hawks have been known to have 20/2 vision, enabling them to spot prey from high in the air.
Most optometrists utilize a version of the Snellen eye chart, invented by Hermann Snellen, a Dutch eye doctor in the 1860's, to conduct an eye exam. While there are now many variations, the chart typically has 11 lines with uppercase letters which get smaller in size as they move toward the bottom. The top of the chart usually shows the uppercase letter - ''E'' with letters being added gradually as you look down the chart. During the eye exam, the eye doctor will look for the line with the smallest lettering you can make out. Each line is given a rating, with the 20/20 row typically being assigned forth from the bottom. In cases where the patient can't read, such as young children or handicapped individuals, a variation of the chart is used called the ''Tumbling E''. At the same scale as the traditional Snellen chart, this variation shows only the capital E in different spatial orientations. The person being tested uses their hand to show the direction the arms of the E are facing: right, left top or bottom. Both charts must be positioned 20 feet away from the patient's eyes.
Even though 20/20 vision does show that the person sees as expected from a distance this test on its own doesn't imply that someone has perfect eyesight. There are many other essential elements that contribute to your overall vision such as side or peripheral sight, depth perception, color vision, near vision and focusing and coordination between the eyes to name a few.
Although an eye exam with an eye chart can determine if you require eyeglasses to see far away it doesn't provide the optometrist a complete understanding of your complete eye health. You should still go in for an annual comprehensive eye exam to screen for potential diseases. Contact our office now to book a Lambertville, NJ eye test.