Lol yeah, you can add the Epsom right to the tank so it might be easier to treat him that way then trying to get meds and him in a hospital tank.
When you do try to catch him and put him in a cup, try feeding him more when he's in the cup, even if he's been fed that day it's okay. And then he can associate the cup with food and not with stress, it will take a while but it's worth it in the end
I don't think he's blind, it can happen for sure but I don't think it's very probable is all. I notice sometimes my boy's don't always go straight for food either sometimes if they're too stuffed or just plain didn't see it like if it's behind them or something. Idk, Betta's a quirky
I hope Blueno get's better soon though!