Vets can’t figure it out anyone seen this before?

My dog randomly (border collie mix German short hair) one day got a prolapsed eye in only one eye . Within two days it went away . Almost immediately after he was fully blind he saw perfectly fine before this . He started drinking water like crazy always and waking up to pee or poop multiple times a night Gradually got less active my thought was from bumping into stuff. 1 vet had me put him on kidney support dog food which helped energy for small amount of time. Now he’s seeming like old man energy which is fine he’s 13 but he’s very runny stools usually and peeing a ton while drinking a lot of water .