Anonymous ID: 335ea8 Feb. 5, 2018, 4:01 p.m. No.279316   ๐Ÿ—„๏ธ.is ๐Ÿ”—kun

"The expression "20/20" is so common in the United States that there's even a TV show named after it. Here's where the 20/20 designation comes from.

 

By looking at lots of people, eye doctors have decided what a "normal" human being should be able to see when standing 20 feet away from an eye chart. If you have 20/20 vision, it means that when you stand 20 feet away from the chart you can see what the "normal" human being can see. (In metric, the standard is 6 meters and it's called 6/6 vision). In other words, your vision is "normal" โ€“ most people can see what you see at 20 feet. (From here on, please assume that the word "normal" has quotes around it)."

 

https:// health.howstuffworks.com/human-body/systems/eye/question126.htm