Sort of a fish's equivalent to dragging one's nails across a blackboard. Unfortunately, pop-eye is really tough to cure. Fixing a pump problem is fairly easy, assuming you know what is wrong with the pump and what to do about it. Bacterial infections, which are the more common cause of pop-eye, are difficult to cure. Antibiotic treatments for the water should be avoided in aquariums other than designated quarantine and treatment aquariums.
Medicated food is an excellent choice if the fish is still eating.
Most of the time, nothing works to reduce the swelling. I don't want to discourage anyone, but the truth is that you should keep your expectations low when a fish acquires this condition. One bright side is that fish that lose sight in one eye often live a fairly normal life with the remaining one. Especially considering that we generally exclude predators from our aquariums. As to your specific situation, it's difficult to know the cause of your Flame angel's condition.