Do Zoro, Nami and Robin suffer from bad eyesight? Although I never noticed in the main story of the anime, there are scenes in some of the openings where Zoro, Nami and Robin are shown wearing eyeglasses:


Zoro in opening 11
Robin in opening 13
Nami in opening 16


Is the fact that they all have bad eyesight canon? Or is it just some filler that the author probably wanted to mix into the series?
Considering they don't wear glasses normally or even while reading, it's fair to say that their eyesight is just fine. They simply like to wear those glasses from time to time for the sake of appearance. Even Sanji wore glasses for a moment in One Piece Film Z, for that same reason.