I have had two fish with bad eyes. A ringneck blenny that was wild caught. Lost both eyes during our big move. Was fine in the tank, being a blenny helped, as he just perched and moved occasionally. Had to hand fed though, was obviously is a PITA. It was our fault so I felt compelled to try my darnest. Live for about 2 months longer, those blennys are difficult to keep regardless.
Currently one of our Chalk basses is missing most of his left eye. Believed to suffered an injury upon introduction from the Lyretail Anthias, either a nip or scrape on the rocks. It's fine at times then swells up out of the blue. Got so bad the retina detached. Has been fine recently, though he's lost part of the eye. He has no problems eating or swimming around the tank.
I think the main problem is aesthetics. Honestly, it's just a bit gross to see the hole where an eye used to be.