While it’s certainly true that eye patches were (and are) commonly used to conceal a missing or disfigured eye, that’s not the most common reason for why pirates wore them.
I’m sure everyone has experienced a time when they had to go from being in a well-lit space to dark one. Maybe someone turned off the lights without realizing you were still in the room or you went spelunking or the power went out. Whatever the experience, I’m sure you remember the discomforting seconds it took for your eyes to adjust to the dark.
Remember that on most pirate ships, there’s at least two levels, above and below deck. The pirates would frequently traverse between the two. By wearing an eye patch, one eye was already accustomed to the dark. So when the pirate went below deck, he would simply lift off the eye patch and go about his business. Now you might wonder Were pirates really so impatient that they couldn’t wait a few seconds for their eyes to adjust?
When they’re pillaging another ship, a few seconds could be crucial. Men defending their goods below deck would already be accustomed to the dim lighting and would be able to get the upper hand on any pirates who entered. But with eye patches, the pirates would be ready for a fight below.
Though these men wore eye patches due to the first reason I listed above, they’re still awesome.
Source: Dr. Jim Sheedy