Who Zoro lost his eye?
Prior to One Piece's timeskip, Zoro's left eye was fully functioning and completely uninjured. Yet when the Straw Hats reunited after their respective adventures, Zoro's left eye was mysteriously scarred shut. Prior to the timeskip, his left eye had been seen glowing when using certain attacks.
Episode 24 | One Piece Wiki | Fandom.
It's entirely possible Mihawk noticed through their duel and training that Zoro suffers from ocular dominance in his left eye. That is to say, the left eye is stronger than the right. As a result, maybe Mihawk scarred the left eye shut and instructed Zoro not to open it until his right eye was trained enough.
One Piece Fans Solve the Mystery Behind Zoro's Eye In it, Zoro, while anxious to advance after showing progress in his training, is quickly humbled by his teacher, resulting in the loss of his eye.