Well, have you fixed up the tank since you went on vacation? The fish is not blind. He has an infection. Cycle a QT. Get the parameters up to par and feed him quality foods dosed with vitamins. He needs medication. Maracyn 2 for SW fish will help him. You need a cycled QT though.
Just for others. QT isn't just for paranoid people worried about introducing things. Stuff like this happens. Then you are stuck. You have to wait for the QT to cycle before you can treat your fish. Think about it.