Pupillary response. Pupillary response is a physiological response that varies the size of the pupil, via the optic and oculomotor cranial nerve. This response results in either constriction (miosis), narrowing the pupil, or dilation (mydriasis), widening the pupil.se of central nervous system stimulant drugs and some hallucinogenic drugs can cause dilation of the pupil. In ophthalmology, intensive studies of pupillary response are conducted via videopupillometry. Anisocoria is the condition of one pupil being more dilated than the other.