There’s always a blacker black and a whiter white. I followed a book once that was supposed to train me to “see without glasses”. Ultimately, likely, mostly a crock but still some useful exercises in there.
One of them I liked: It’s to improve contrast-ability in your brain so that your vision has a more ‘contrasty’ place to go:
You close your eyes and imagine the blackest black you can imagine.
Go as black as you can.
Hold it there.
Then, go one shade blacker.