Pupil changes

Do you see this response with the light shining continuously on one side? If you are it could be a 'relative afferent pupillary defect' related to an optic neuropathy (compression?). Are you moving the light from side to side fairly quickly? If you are, then this is a normal response. If you see alternating constriction and dilatation that seems rhythmic, that is called 'hippus' and it's usually normal too.