Popeye is a symptom of something, either an injury or a bacterial disease process. What are the symptoms, how long have you had the fish? Has the fish been healthy?
Can you setup a hospital tank? If the problem is an injury, then the eye will likely heal on its own. If it is a bacterial infection, then you will need to setup a hospital tank and treat with Maracyn2.
Is the fish still acting and eating normally?