My cat at the vet a few years ago after his BFF scratched his right eye (I think), resulting in it being swollen shut. I had to administer an ointment to it daily for a few days until it went back to normal--the ointment had the side effect of making his pupil absolutely huge. He took it like a champ, though, and fully recovered with no complications.
I'm not sure why but the two different eyes make him look like a terrifying murder kitty lol
I'm sure he's a wonderful cat in person