He might not like it much but you could try shining a light in that eye to see if the pupil retracts. I wouldn't hold it really close or use a bulb that was too bright so you don't hurt his eye. Even if all he does in response is to close that eye to the light, that would be positive. It's possible he's blind in one eye, I dunno. As long as he acts normal and gets enough to eat I wouldn't worry too much. Watch how he acts around food, if he can't see out of one eye he much be a slow hunter. You might try to figure out a way to separate your frogs during feeding so that the other guy doesn't snatch all the food first. Are they eating crickets or fruit flies right now?