Pop eye is a condition caused by stress and or poor water quality. It is usually associated with another kind of sickness that made the fish stressed out and can usually be reversed if provided with a non stressful, healthy, clean enviornment. If you see any other symptoms; not eating, swimming up and down in the same spot, constant corner hugging, gasping for air, etc. You will need to setup a quarentine and find the root of the problem.
For now just provide a good varied diet and wait to see if it gets worse. fwiw, i have an eight line wrasse in my 210 that has had popeye for three weeks and is fine still lol. I can't catch him as there is 250lbs of live rock in the tank and my corals have grown bigger than the opening, so i am waiting it out.
good luck bud.
austin