It’s generally assumed that “20/20” is perfect vision, but what does this mean?
Visual acuity is the term used to describe the sharpness of your vision. When doctors do a visual acuity test, they have you view something (usually the Snellen eye chart of letters) from a standard distance and tell them what you see.
One of the lines on the eye chart has letters that are a size which is known as “20/20 visual acuity,” meaning that at 20 feet, most people can accurately read those letters. This standard, at 20 feet, means you read them as well as someone else at the same distance can read the letter accurately.
Visual acuity of 20/20 is considered “perfect vision” because no aids are required, but people can have better than 20/20 vision. Many are able to see letters smaller than the general “20/20” size.
Others can read smaller letters which would be 20/15 or 20/10 visual acuity, meaning at 20 feet, they read letters that most people can only see clearly at 10 or 15 feet.
For those with less visual acuity, they may be 20/40 or 20/60. The largest letter on the chart (an E on most Snellen charts) corresponds to 20/200 vision. If someone cannot distinguish that letter without assistance, they are considered legally blind.
Some can pass a visual acuity test sufficiently but still have “high-order aberrations.” The eye doctor may find that you have coma, spherical aberration, or trefoil. These can produce symptoms including bad night vision, double vision, starbursts or halos, glare, or blurring. Low-order aberrations are familiar to most people as nearsightedness, farsightedness, and astigmatism, but high-order aberrations are less well-known.
Of course, if you want to know your visual acuity, a comprehensive eye exam is the best way to assess it. Set up an appointment today to and learn what options are available to help you get perfect vision!