What is 20/20?
Vision or visual acuity is tested by reading a Snellen eye chart at a distance of 20 feet. This chart sets a standard for what most people should be able to see when they stand 20 feet away. If you have 20/20 vision, it means that when you stand 20 feet away from the chart you can see what a “normal” human being can see. (In metric, the standard is 6 meters and it’s called 6/6 vision).
If you have 20/40 vision, it means that when you stand 20 feet away from the chart you can only see what a normal human can see when standing 40 feet from the chart. That is, if there is a “normal” person standing 40 feet away from the chart, and you are standing only 20 feet away from the chart, you and the normal person can see the same detail. 20/100 means that when you stand 20 feet from the chart you can only see what a normal person standing 100 feet away can see. 20/200 is the cutoff for legal blindness in the United States.
You can also have vision that is better than the norm. A person with 20/10 vision can see at 20 feet what a normal person can see when standing 10 feet away from the chart.
This chart will demonstrate to you the degradation of vision that occurs as your eyesight progresses from 20/20.