The degree of power characters have is directly proportional to how many eyepatches they wear and/or how big they are, or at least everyone thinks so. Characters will voluntarily put out their own eyes to become more powerful.
A character wears a patch over each eye, meaning he's twice as tough as anyone with just one.
One of the other characters eventually snaps "take that damn eyepatch off!" — turns out the eyepatch-wearer only wears it to look tough, and has perfectly functioning eyes.
Someone with more than two eyes (say, aliens or monsters) put on eyepatches on all eyes except one, and by this trope become the most powerful combatant in the universe.
Zig Zagged: The badassitude of the character with an eyepatch varies widely at different points in the story.
Averted: Characters in the series who have eyepatches are no more experienced with fighting than the ones who don't.
Lampshaded: "Don't mess with me or my badass eyepatch if you value your life!"
Invoked: A character with two fully-functioning eyes starts wearing an eyepatch in the hopes of increasing his badassery as a consequence.
Exploited: Bob takes advantage of the eyepatch guy's blindspot.
Defied: When he loses an eye and starts wearing an eyepatch, a character refuses to go into combat situations anymore after the incident.
Discussed: "Watch out- one of the guys on the other side has an eyepatch. Probably means he's really strong- I saw a movie like that once."
Conversed: "Hey, look at that guy with the eyepatch in the background! Bet you ten bucks he takes down the entire opposing side."
Deconstructed: The consequences of having an eyepatch are explored - the character may be more experienced in combat, but the loss of depth perception makes him vulnerable. The eyepatch may be a Magic Feather.
A Person lost their eye in an earlier fight, and trains hard to make sure he isn't caught off-guard again.