Ever wonder what 20/20 vision actually stands for? The phrase 20/20 vision represents normal visual acuity or clarity of vision. In other words someone with such eyesight can see an object clearly from 20 feet away that the majority of people should be able to see from such a distance.
In cases of individuals that cannot see an object clearly at 20/20, their visual acuity score is determined based on where they begin to see clearly compared to what is normally expected. As an example, if your acuity is 20/100 that indicates that at 20 feet you can only see an object that the standard would see from 100 feet away.
An individual whose vision is 20/200 or worse is considered legally blind however, they can often achieve much improved eyesight by using glasses or contacts or by having LASIK if they qualify.
Most eye care professionals use some version of the Snellen eye chart, invented by Hermann Snellen, a Dutch eye doctor in the 1860's, to perform an eye screening. While today there are quite a few variations, the chart typically has eleven lines of uppercase letters which get progressively smaller as they move toward the bottom. The top of the chart usually shows one capital letter – ''E'' with the addition of more letters as they get smaller. During the eye exam, the eye doctor will assess the line with the smallest lettering you can see clearly. Each row is given a rating, with the 20/20 row usually being ascribed forth from the bottom. For small children, illiterate or handicapped persons who are not able to read or vocalize letters, a different version of the chart is used called the ''Tumbling E''. At the same scale as the traditional Snellen chart, the ''Tumbling E'' shows only the uppercase E in different spatial orientations. The patient uses their hand to point to the right, left, top or bottom based on the direction the E is facing. Both charts must be placed 20 feet away from the patient's eyes.
Even though 20/20 visual acuity does indicate that the person is able to see as expected from a distance this metric alone does not imply that the individual has perfect vision. There are a number of other essential abilities needed to make perfect vision such as side or peripheral sight, perception of depth, focus for near vision, color vision and eye coordination amongst others.
While a vision screening with an eye chart can conclude if you need glasses to correct for distance vision it will not provide the optometrist a comprehensive perception of the overall status of your eyes and vision. You should still schedule a yearly comprehensive eye exam which can identify potential diseases. Call us today to schedule a Raleigh, NC eye test.