There is a theory that the main character, John Marston, has a weakened or blind left-eye. Evidence supporting the theory is Marston's "Deadly-Assassin" outfit which includes an eye-patch that goes over his left-eye, during cut-scenes Marston seems to turn his head over to the left slightly to possibly see more with his right eye, sometimes when using Dead-eye, Marston will comment "I think like I got my eye back", after Dutch Spoiler:shoots the woman during Great Men Are Not Always Wise, John does not take the opportunity to shoot Dutch as he runs through the doorway on John's left side. The other lawmen make a comment towards John about not shooting him, too.And the Undead version of John Marston has a missing left-eye.

There's also another interesting bit hinting at this, which is a comparison between John Marston and Johnny Klebitz from Grand Theft Auto IV; Both share similar names (John/Johnny), both rode in gangs that left them both for dead and come from rough (and criminal) backgrounds, both have antagonists named Bill/Billy, both had a girlfriend/wife that was considered "every man's", both are forced to work with the government to save themselves and those they care about, and it is implied Johnny has a weakened/blind eye. ("Oh. I should use my good eye.")