Help my Unicorn Tang

[Goodwin9]

I need some help! My Unicorn tang has developed an enlarged eye and I am not sure what has caused it, or what I can do for it. I've had the fish for 2 years and it is about 7" long. Can anyone offer any advise on what I can do for this?
Good eye;

Bad eye

 

[Percula9]

Your fish has popeye. Remove to a sick tank, and treat with Furan2 for 7 days. If not treated he will lose the eye. This happens when the fish scrapes the eye on a rock, then bacterial infection sets in.

 

[davenia7]

If caught early,treatment may not be necessary, but that case is not an early catch.
I agree with above. Also, do some WC's on the whole tank.

Also what are your parameters and WC sched.? Pop-eye is more common when Parameters are off or you missed your sched. WC.
ie. cootie water.