Powder blue tang white ring

[fishandsail]

I woke up this morning to find my powder blue tang having this weird white ring by his face. There's a small dot in the middle if it's unseeable in the picture. Does anyone know what this is and/or how to treat it? This is my prize fish, so I'm kind of geeking out at the moment.

My blood red shrimp has been kind of helping him out trying to act like a cleaner shrimp and getting on him to pick it off, but who knows...

http://imgur.com/zpdJZ

EDIT: forgot picture link.