Popeye is not really deadly, and it is very treatable. You need to decide if you want to return it, or if you want to go thru the trouble of treating it. How long have you had it and what type of tank is it in? Popeye is not contagious, however, if you end up having to use antibiotics, then you may want to consider returning it, or investing in a hospital/QT---which everyone should have anyway.
Give some of your tank info. What type, how old, big, what's in it. In your opinion, how big is the eye poped out? Is the eye cloudy, red, does the fish focus or see you using that eye?