I came across that when I looked up some differentials, and remembered learning about it way back in parasitology, but couldn't remember if that was a common thing or how to treat. Thanks for bringing it up and mentioning the treatment!
I'm so sorry for your loss. He was a beautiful rabbit.
The movement of the eyes like that is called nystagmus and it can be a sign of nerve damage, brain damage, or middle/inner ear damage. That combined with the head tilt makes me suspect he might have had some vestibular issue going on, but...