Does he jump in the water when you come near the tank? It is probably natural that he doesn't really leave the water, since their defense from predators is jumping in the water. He probably feels very vulnerable not being able to see. Will you be able to take care of him? A frog that can't see will require a lot of care, especially being a bullfrog. Im sure feeding time of a blind frog is hysterical! Do you have a 100 gallon set up ready?