personally, I would keep him, especially seeing that he ate. He may be hanging in a corner to adjust to his new unfortunate circumstance, who knows. What is important though is what else is in the tank, if you are absolutely sure he didn't lose his eye to pecking (which is not so uncommon for barbs and tetras in establishing order), your next need is to find out if it was due to an infection. For a fish to one day appear with no eyes though, screams pecking to me.
Keep an eye on him, if he continues to eat, he may adjust to his surroundings and be able to handle things as a blind barb. It's all your feeling on it though.
Again, if it was me and since he ate, I would save the Eugenol for another day.