Yarrrrr!
A true pirate always carries spares. Be prepared! Or is that something else.... :)
Ah, now I've been thinking about this.
Wearing glasses (as I occasionally do too) would mean you would need only two patches, the average pirate traditionally only covering 50% of his/her ocular capacity at any one time.
Two eyes - one patch
Four eyes - necessarily, two patches
Unless perhaps you were some kind of arachnid pirate.
"Anansi-the-pirate" required, as the story goes, indeed four eye patches.
so there you go!