Intresting to note that one of my horses is blind in one eye, has been since he was 2 yrs old, has LONGER whiskers on the blind side. Creepy long, actually. LOL And I've watched, and yes, he's using them to feel around on that side of his face (all his whiskers, not just his eye ) If he swings his head around to see something and his whiskers touch something he stops.
But, we used to shave them all off for shows and none of the horses ever seemed to have any problems with it. I leave them now because I don't show, and I would leave them on the half blind horse regardless.