Could be PopEye. Only had this happen a few times and the fish were just removed and let heal on his own. Some made it made it some didn't. My fault for not wanting to use the meds.
Live and learn though.
Even us SO CALLED experts make mistakes.
Exophthalmus or Protruding Eye
Sometimes a disease occurs in a fish in which the eye swells and becomes too large for thr orbit.
Exophthalmus can be caused by bacteria, namely, some strains of Pseudomonas punctata, but in several cases no bacteria has been found on wounded fish. thus leading to believe that it is not so much bacteria related but can also be caused by preasure or blows to the head. That like aggressive behavior from tank mates.
Hope this helps
Danny
Now this is a bit diff. than the traditional PopEye which yopu can get meds for at any LFS. Both show simmular symptoms only way I ever found a diff. was the ones that died were NBOT Pop Eye which in most cases the fish tends to wither away.