Yes but those are well-known and visible to the naked eye. I've never heard of these 'micro-dilations' and Google didn't show anything.

'hippus', specifically 'physiological hippus', or ' pupillary athetosis', seem to be the correct terms for what I was describing as 'micro-dilations'. Saccades, as I understand it, is rotational shift of focus by 1-2 degrees, rather than repeated contraction/relaxation of the pupil.

I think you're thinking of microsaccades.

Saccades in general are just rapid, ballistic eye movements: they don't have to be small and they're often voluntary. You often make saccades without explicitly thinking about it, but you can countermand these and hold your eyes still when you want to.