Justin Bieber has perfect vision. He does not have contacts or other prescription glasses. He wears all types of glasses, such as different colored sunglasses, goofy glasses, big sunglasses just for fashion purpose. Among all eye he wear, chic nerd glasses are his favorite.
He wears glasses only for fashion because he doesn't have vision problem. Many celebrities who have perfect vision like to wear sunglasses for fashion purpose. The glasses make them appear attractive and sexy.