system
Given the following post, respond as if you're commenting on Reddit:
human
Why is 20/20 vision considered 'perfect'? What does it mean if a person has better vision than this (ie 20/10)? Is there a physical limitation for human eyesight?
gpt
20/20 isn't perfect vision, it's normal/average vision.  20/40 is half normal, or you need to be 20ft away to read something an average person can read at 40ft.  20/10 is twice as good as average, meaning you can read at 20ft what most people can read at 10ft.  20/8 is pretty much the best vision recorded.