What happened to Zoro's eye?

In the two-year time skip, Zoro trained under Dracule Mihawk, popularly known as Hawk Eyes Mihawk. One of the popular theories is that the scar on Zoro’s left eye is a training mishap. Many believe that Zoro lost his left eye during his training in some sort of accident or battle.

This is one of the most intriguing and plausible fan theories. Ocular dominance is defined as a condition in which one eye is utilized more frequently, has greater vision, or is better able to focus than the other. Now, Zoro’s poor sense of direction is no mystery, and he often gets lost. Ocular dominance might be the reason behind Zoro’s poor sense of direction. Now, in his profession and to fulfill his dream, perfect eyesight plays a major role.

So this theory suggests that Mihawk noticed this and scarred Zoro’s left eye, which is supposedly suffering from ocular dominance, and instructed Zoro to keep it shut until he trains his right eye to become strong enough.

Zoro is one of the strongest swordsmen in the One Piece series, aspiring to become the strongest. Zoro has surprised his fans on multiple occasions with his eye-catching powerful techniques. One of his most popular and strongest techniques is his Demon Asura technique, the infamous Nine Sword Style.

There is a popular fan theory in circulation that Zoro is cursed and possessed by the spirit of Asura, the demon god, as a side-effect of his cursed swords. This theory suggests that Zoro's left eye is shut to keep his demon prowess in check.

According to a widely accepted fan theory, Zoro has Conqueror's Haki and uses his left eye to activate it. Oda has emphasized the user's eyes, in contrast to Conqueror's Haki, which adds some weight to this theory. Although it is not stated or revealed up until now, there is some evidence that suggests Zoro might possess Conqueror Haki.

The possessor of the Color of the Supreme King has some peculiar traits. Some of these traits are that they are fearless, determined, and never back down, all qualities that Zoro possesses. In addition to that, in the Punk Hazard Arc, some believe that Zoro used Conqueror Haki against Monet as she was paralyzed and couldn’t move a muscle. Interestingly, before the two-year time skip, Zoro was often mistaken as the captain of the Straw Hat Pirates and he even acted as a captain.

In conclusion, there are many fan theories about Zoro’s left eye, some more plausible than others. Despite that, these are still just fan theories and although they are plausible, that doesn’t make them true. In the end, we won’t know anything for sure until some information comes to light regarding the matter in the manga, anime, or from Eiichiro Oda himself.