Clearing Up the Meaning of 20/20 Vision
With all of the complicated terms associated with vision, from prescription coordinates to the myriad of eye condition terms, one might think that "20/20 Vision" would have a far more complicated meaning than it does. In fact, you may be surprised just how simple the basis for 20/20 vision is.
When a patient takes a basic "eye chart" vision test in their eye doctor's office, they are undergoing what is referred to as a visual acuity test. This test utilizes a "Snellen chart," which you may know as that white chart with progressively smaller lines of letters moving down the chart. From twenty feet away, with one eye covered, the patient reads aloud the line with the smallest text they can see clearly. This is repeated with the other eye covered. Results usually determine whether or not a patient may need corrective lenses to improve their vision.
While 20/20 vision refers to "normal" quality eyesight, what 20/20 actually means is this: At 20 feet from the chart, a person with "normal" vision can read the smallest line of text with one eye closed. Therefore, that person can see at 20 feet away what a person with "normal" vision can also see clearly from 20 feet away. Someone with 20/40 vision must be no more than 20 feet away to clearly see what a person with 20/20 vision can see from 40 feet. This measurement scale continues upward in 20-foot increments to such distances as 20/200, which is considered legally blind.
As much as the term 20/20 has become synonymous with "perfect" vision, this is simply not the case. There are many people who sport 20/15 vision. 20/15 vision means that individual can see objects clearly from 20 feet away that people with "normal" vision need to be 15 feet away to see. There are also vision researchers developing vision technology that can reportedly improve an individual's vision to somewhere in the range of 20/5. There are differing opinions in the optical world as to how practical this level of vision would be to the general public.
Whatever your visual acuity, hopefully, this information helps clear up any confusion you may have about the term "20/20 vision." If you have questions that have not been answered here, consult your eye doctor.