Zoro Left Eye. During this time each member of the Straw Hat. During and after the two-year timeskip Zoro gains a new scar running down over his left eye which is now implied to be critically injured as it is always closed.
At the very least fans know that it happened sometime during the two-year time skip. Fans have yet to learn just how Roronoa Zoro had lost his eye as when the swordsman of the Straw Hat Pirates returned from the time skip he was missing the important extremity. The most prominent change in his appearance after the time skip is the scar across his left eye.
Everyone saw and noticed the scars on Rayleighs body and eye were almost identical to Zoros.
During and after the two-year timeskip Zoro gains a new scar running down over his left eye which is now implied to be critically injured as it is always closed. It is only observed that the scar has caused some major damage to his eye causing him to keep it shut. The energy is so built up and focused when the eye is opened he unleashes a great force like a haki blade. His Haoshoku might be at a stage in which Luffys was previously only emerging during emergencies and times of crisis.