So, why do pirates wear eye patches?

It's probably not what you think..



From Wikipedia: Sailors (stereotyped by the eye-patch-wearing pirate) who often went above and below deck, might have used eye patches to have one eye adjusted for the top deck and the other eye already adjusted for the darkness when suddenly going below deck. The strong sunlight while above deck on an oceangoing vessel could require minutes of adjustment to the dim lighting below deck. With virtually no light sources below deck, sailors would have to rely heavily upon their eyes to adjust. In the critical moments of modifying the rigging, navigating, and especially during battle, those minutes were too precious. A simple switch of the patch from one eye to the other might have saved time when going between decks, pirates wear eyepatches.

Similarly, pilots at one time would also do the same, when flying at night over brightly lit cities, so that one eye could look out, and the other would be adjusted for the dim lighting of the cockpit to read unlit instruments and maps.

When flashlights with red bulbs, backlit instruments, and other modern instruments came along, that no longer was necessary, just as boats and ships evolving into being well lit made eye patches a thing of the past.