What does 20/20 vision mean?

by Dr. Dan Laby

Is 20/20 normal vision?

I am often asked what is “normal” vision. You can imagine that it is a difficult question to answer. I often answer normal for whom? The Vision needed by one person may be very different than the vision needed by another. Imagine a librarian who needs to spend most of the day reading or looking at things up close. That person would do very well with less than 20/20 vision, and in fact would benefit from being a little nearsighted. The nearsightedness leading to less than “normal” 20/20 vision at distance would be helpful in reading.

Consider now a professional athlete – say a baseball player. For the baseball batter we know that “normal” 20/20 vision is not good enough and that the average vision of a professional baseball batter is actually 20/12. So in one case vision less than 20/20 is normal, for the librarian. In another case, vision better than 20/20 is normal, for the baseball batter.

So that leaves us with the question is 20/20 normal vision?

What does 20/20 actually mean?

This question was answered (somewhat) many years ago when the 20/20 fraction was first used. 20/20 is simply a fraction, a comparison between what you see and what a normal person can see. For example – if your vision is 20/40 that means you can see from 20 feet what a normally seeing person can identify correctly from 40 feet. Thus, you are less than normal since you need to be 20 feet closer to see the same thing.

On the other hand, if your vision is 20/15, then you are better than normal since you can see from 20 feet what the normal person can only see from 15 feet – you can see it from 5 feet further away.

So in the fraction, the top number is how far you are from the target and the bottom number is how far a normal person is from the target!

The numbers can be noted in feet as in 20/20. They can be noted in meters which would be 6/6. Lastly, they are even sometimes written as a decimal with 20/20 being 1.0, and anything less than 1 being less than normal. For example, 20/40 would be 0.5. Anything greater than 1 being better than normal. For example 20/15 would be 1.33.

So what is normal vision?

Remember, normal is a very misleading word. For example it’s not normal for a 4 year old to be able to see 20/20. Their visual system is not yet mature and developed enough to see that well.

It is also not normal for many athletes to see 20/20. For example, as noted above the average vision of a major league baseball player is 20/12, for a professional soccer player it is 20/15, etc.

So the 20/20 normal answer is very general and is essentially for the general population. It likely does not apply to your sport – the notation is the same, but your sport may require better vision than 20/20 – such as 20/15, 20/12, 20/10 or perhaps the limit of vision – 20/8.

More on that limit of human vision in our next post. For now, we understand the notation – stay tuned!