It could be just a peck injury or it could be a respiratory problem which could be many things (many of which are bad.) I would separate it right away in case it is respiratory, but also for it's protection since he can't see well and may be pecked more. Clean the area around the eye with warm saline (or weak salt water.) Terramycin eye ointment (available from farm stores) or erythromycin ointment are good for eye infections and injuries. If desperate, plain neosporin would be okay until you get terramycin. Apply 2-3 times a day, and clean the eye area when needed for drainage. My polish chick looked like that a few months ago after being pecked, and I thought her eyeball was ruptured, but within a week it was back to normal. Wishing you good luck. If other symptoms such as sneezing, labored breathing, or other respiratory symptoms show up you may need to treat for CRD or coryza.
I would keep him seperate from others and clean the eye with warm water. Maybe some tetriclicine(sp) I believe that the eye ointment in the tiny tube. Clean the eye several times a day if needed. Maybe antibotics in the water also. If its not just the eye and is CRD then tylan 50 injectable in the neck 3-5 days and 1/2cc.