Can one have 20-40? What does it mean to have normal vision? What does the by merator and denominator mean?
In: Biology
20-20 vision is “normal” unimpaired vision. Specifically, it means that someone with that vision sees something 20 feet way as clearly as someone with normal vision can.
20-40 vision means that they see something 20 feet away as clearly as someone with normal vision would see it from 40 feet away.
The numerator is “number of feet away that you can still see details”. The denominator is “number of feet away that someone with normal vision can still see details”.
So 20/40 means “while someone with normal vision can see details from 40 feet away, **you** need to be 20 feet away to see the same details”. So your distance vision is worse than normal.
The two numbers are a comparison. 20-20 means you can see at 20 feet the same level of detail that a “typical good-sighted person” can see at 20 feet. The first number is you, the 2nd number is a group average. The numbers are distances in feet.
10-20 vision is bad. It means your detail limit at 10 feet is what good-sighted people can see at 20 feet. This person would need glasses for distance vision.
30-20 vision is good. It means you can see at 30 feet details that typically can only be seen at 20 feet. Pro baseball players tend to have better than 20-20 vision because it helps them see the pitcher’s grip and ball spin on the pitch.
So yeah 20-20 isn’t the max or anything, it’s just how you compare to the level o
Latest Answers