injured or infected?

by cathy
(u.s.a )

my red eared slider has one eye that won't open but the other is fine. I put the turtle in with the other red eared slider while i was changing its water and i cant tell if it was attacked by the other one or infected.

I'd like to know before i have to take it to the vet just in case it can heal by itself. I know they used to attack each other so i seperated them. My turtle still looks fine without the bad eye and still likes to stay on his rock, i think he eats.
hurry before its too late!!