This is a very common question. 20/20 vision is something you hear about all the time and we all want 20/20 vision, right? So, what does it mean?
First of all, 20/20 vision does not mean perfect vision. Instead, 20/20 vision means 'normal' vision. This is a kind of standardized measurement, eye care professionals use to classify the quality of your eyesight.

Snellen ChartAnd what do those numbers stand for? The first number means 'twenty feet' or about 6 meters, which is a distance at which eye doctors measure whether you can see certain letters on a chart (such as the Snellen Chart). The second number is a standardized way for a normal eye to see those letters at twenty feet away. So, if you see 20/40, that means you see half as well or in other words: You see something at twenty feet what a normal I can see at forty feet. And for the other way around: if you have excellent vision and you have 20/10, that means your vision is twice as clear as that of a normal eye. You can see something at twenty feet what a normal eye can see at ten feet. So it is really good if you have 20/10 vision.

A common follow-up question is: What is legally blind?

Most official health agencies and institutions define legal blindness as a condition, where your eyes can see something at twenty feet what a normal eye can see at two hundred feet or further. Legal blindness is also occurring when an eye's peripheral vision is limited to twenty degrees or less.