Slightly different from an alternate definition that refers to the triangle patch of fabric or whale tail near the top of the thong, this varient is specific to exposed penumbra of flesh around the butthole which combined with buttfloss looks like an Eyepatch a pirate might wear.
As the English language deteriorated over time into various forms of slang, the word "eyepatch" was introduced into society. Thus, incorrectly replacing "pirate patch."
Son" You mean an eye patch?
Tina: Nooo it's really called an pirate patch! Look it up on urban dictionary!
Son: Oh, you're so right, it IS called a pirate patch. I'm so stupid and you're so smart Tina.goshhhh
"the brown eye"