your turtle most likely has pink eye, Just like you bacteria has gotten in its eye, this comes from poor water quality. Red ears are not as prown to this as other turtles, maps and softshells. You need a topical antibiotic this will cure him up in a week or so. turtles have a slow recovery, so it will take a little time. but to keep this from happening again make sure that the water is clean, because if you dont shell rot will be next and that is far harder to get rid of and can permentaly damage you turtle.