Do you have any other symptoms? Like turning more one direction the the other? If you pinch toes on each foot, does he respond equally on each foot, ie pull back a paw. If you sit in front of him on the floor, take a pair of forceps or a pen, brush them across the whiskers ends. Does each side react the same, ie does his face twitch like tickles. Wave a hand, coming from behind the ear, in front of each eye. You would like to see him close each eye. Any squinting when he goes from inside to out into the bright light? Like we would so with a bad headache? I have several others if you'd like some more.

It is probably a muscle spasm. That's why the steroids are helping. they can last for days until it resolves by itself. It looks like you should look for a new vet.