Let me see if I get this.
20/20 means that you can see things from 20 feet distance that people on average can see on 20 feet. Meaninga 20/20 vision is just average. A perfect vision would be something like 20/0, where you can see things from 20 feet that people need to look at very closely at. (And 20/200 means that you need to stand 20 feet away to see the same clarity that an average person at 200 feet away sees.)
20/20 means that you can see things from 20 feet distance that people on average can see on 20 feet. Meaninga 20/20 vision is just average. A perfect vision would be something like 20/0, where you can see things from 20 feet that people need to look at very closely at. (And 20/200 means that you need to stand 20 feet away to see the same clarity that an average person at 200 feet away sees.)