Could he have been pecked in the eye and damage was done to the conjunctiva tissue or the third eyelid (nictitating membrane?) Do you have other cockerels or roosters? I would flush the eye with some saline eye wash, and apply some plain antibiotic ointment or drops 2-3 times a day. Terramycin eye ointment is found in some feed stores. Plain Neosporin is over the counter. Or a family member might have some antibiotic drops from a cataract surgery or procedure.