Hard to tell if it has Popeye. If it does, I would treat with Maracyn and Maracyn 2 (see links below):
http://www.fosterandsmithaquatics.com/product/prod_display.cfm?pcatid=4838
http://www.fosterandsmithaquatics.com/product/prod_display.cfm?c=3578+4615+4629+4842&pcatid=4842
Make sure you get the ones for Saltwater. If needed, you can also use Copper and PraziPro with Maracyn 1 & 2. Please note Maracyn 1 & 2 is *NOT REEF SAFE*. You'll have to catch the fish and use a QT. Also, Maracyn will turn your water a yellowish color so don't be alarmed by that. Use carbon to remove the medication when you're done, and I also recommend water changes after you're done treating.
Read the directions for those treatments, if the eye isnt clouded over its not popeye and popeye normally affects both eyes. Single eye swelling with the eye remaining clear is usually a result of a trauma to that eye. The cure is to reduce the swelling in the eye and let it heal naturally. Maracyn and others wont do anything for this fish except to prevent a secondary infection. In this case the treatment would be worse than injury, once you add the stress of catching the fish and removing it from its habitat.
If you were to QT a fish, how long do you use the epsom salt?
My fish also has an eye infection and I thought it was pop eye but its only one eye that's cloudy and swollen. It kind of looks like it might fall out. Reading this post it mentioned pop eye affects both eyes so I figured it isn't that. The fish has brown discoloration around the infected eye as well. Would epsom salts work on this fish because I can't order meds offline due to the long shipping time.
i dont know for sure but it couldnt hurt. Espom salt will reduce the swelling and will help heal the wound. Is the fish eating and acting normal? I would use it then let us know what the eye looks like in 4 days.