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.
And 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 eye 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's 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.