*nods and agrees with Imw80*
First line of defense with popeye is fresh clean conditioned water. In the case of popeye, there are a number of things which might have caused it: poor water parameters, bacterial infections, viral infections, parasites. By making sure the fish is in water with proper parameters (no ammonia, no nitrites, low levels of nitrates, correct levels of salt in the case of mollies and the right temps), you can reduce the level of stress and help improve the fish's immune system. Generally broad spectrum antibiotics are the best treatment; they will obviously not affect a viral infection. There is also no guarantee the eye will reduce once the cause is removed; however, bulging eyes do not seem to affect the fish's quality of life once the cause is gone.