To become an air force pilot you don't have to have 20/20 vision but it's much better to have 20/20 vision when flying.
However all you need to become an air force pilot is a vision that is no worse than 20/70.
As long as your vision is not worse than 20/70 then you can usually pass the vision test for becoming an air force pilot.
Having 20/20 vision means that you have normal vision but the eyesight doesn't have to be that good but if your eyesight is worse than 20/70 vision then you won't pass the eye exam to become the air force pilot.