Vision is measured by eye charts placed at standard distances from a patient. The Snellen eye chart is the standard eye chart used for measuring visual acuity in eye clinics as well as many physicians’ offices. The first number, the 20, refers to the distance that the patient stands from the eye chart, conventionally 20 feet. The second number is the distance at which a person with normal, good vision would be standing to read the same letter that the patient reads from 20 feet.
For instance, suppose a patient has terrible vision and is recorded at 20/200—this patient, while standing 20 feet from the eye chart, can read only at a level that a person with normal, good vision could read while standing 200 feet from the eye chart. Therefore, a patient with 20/20 vision has good vision and is able to see the same letters on the chart as a normal person at 20 feet. Another example would be a patient who has 20/50 vision. This patient’s vision is somewhat compromised, and when standing 20 feet from the eye chart, he or she can only read the same letters that a person with normal, good vision could read while standing 50 feet from the eye chart.
Occasionally, patients have vision that is better than 20/20, and they might be recorded as 20/15. This means that when they stand 20 feet from the eye chart, a person with nor-mal, good vision would actually have to move closer and stand 15 feet from the eye chart to see the same level. When individuals see better than 20/20, it means their vision is better than the normal standard for visual acuity. Nick’s comment: I have one eye at 20/20 (the eye that received Lucentis) and one with no central vision. My peripheral vision in my poor eye is extremely important and a great help to me.