Did you know that pirates didn't wear eye patches because they were blind in one eye? I always thought they wore them because they didn't want people to be grossed out by their blind eye. But that isn't true. (Probably) Have you ever heard of a considerate pirate? I didn't think so.
Pirates wore the patches so that they can quickly uncover their eye in a dark place and be able to see. It works--try it out yourself! If you think about it, it makes sense. The pirate would jump on the deck of the ship he was taking over and take care of everyone on the deck. Then he would have to go below deck in almost complete darkness and it could take a minute or to for the pirate's eyes to adjust. He was fighting in the bright Caribbean sunlight, after all. This way the pirate could storm dark rooms with his guns blazing.
This hasn't been supported by any historical data, but that just means the pirates didn't keep a diary. Of course they didn't keep a diary! They're too busy taking over ships to write down why they use an eye patch.
I've actually used this technique myself when I go the bathroom in the middle of the night. When I turn on the light in the bathroom, I keep one eye shut. When I'm done and I'm heading back to bed, I open the other eye that is used to the darkness. That way I don't trip over Olivia's toys or step on anything. It's pretty great.