This is the real reason for why pirates used eyepatches

Turns out eyepatches were not just an evil-looking accessory. They were helpful for living the sea life as well. The sunlight on the ocean is magnified and could take the sailor minutes to adjust to the darkness below deck otherwise. With an eye patch, all they needed to do was switch and cover up the other one, which had stayed in the dark for a while already. It wasn't just pirates who used the eye patches, either. Sailors in general who were often going above and below deck would wear the eye patch.