I remembered asking myself the same question anyway i fin 3reponses
1-when Oda showed him with his background story ( when he was little )
he had't any problem and his left eye was visible
2-In Alubarna he had a fight when i saw his left eye without any apparent problem

3-I remember everytime in the moviesand in the anime when he sees a beautifull lady his eyes turn to hearts so i think his left eye is normal
So i may have i think given an appropriate answer even if i'm a little drunk now

(i even drunked rhum the alcohol of mrines and pirates...

^^; )