Thanks everybody. I gently tried to get it out of the big tank tonight, but it is way too wily. I won't try again because I read in sushigirl's link that it might have been trauma-related and the last thing it needs is more possible trauma. It may have gotten banged around some in the tank move - I can't remember if his eye was slightly enlarged before or right after the move.
Because it is one eye only, is it reasonable to assume it is not a contagious thing? I just want to keep everybody healthy.