Is it just his eye, or some of his face/head. or sinuses. It might be infectious sinuses. You can treat it with Tylan, you can put it into their water. It is ok for birds that arn't infected to drink it also, just you can't eat the eggs/bird while its on it, it needs sometime for the medication to withdrawl from the body. They also have injection, but I have always used Tylan.
One of our turkeys has swollen eyes, but is still eating and drinking fine. We looked for Tylan at TSC and they only carry is for swine and cattle. Is there anything else we can give it?