Wow....that's a very serious problem, I think. That's not a typical "stuck eyecap." It might be multiple layers built up over a long time, but again, when it gets that bad, it's a lot more serious. You may need to take him to a vet and get that looked at. (Not just any vet, but one with experience dealing with reptiles and snakes)
Edit for additional thought: You can cause more injury to the eye by messing with it, so other than the soaks where he can try to rub on it himself, I would not mess with it at all. Don't try to "pull" anything off because it might not be what you think it is and you could make things worse.