WHY do pirates wear a black eye patch? A black eye patch help | Why?

WHY do pirates wear a black eye patch?

A black eye patch helps rapidly get accustomed to changing light.

Not only pirates wore such blindfolds. Any sailor who needed to go down in the hold frequently wore an eye patch.

The ocean, reflecting sunlight, blinded the eyes, but it was truly dark in the holds. The sailors kept one eye in constant darkness, though when they went down into the hold, they opened it and saw well at once.