Pupil Size

Morphine and most μ- and κ-receptor agonists cause constriction of the pupil by an excitatory action on the parasympathetic nerve innervating the pupil. Opioids release cortical inhibition of the Edinger-Westphal nucleus, resulting in papillary constriction. It has been demonstrated that alfentanil in a dose-dependent manner attenuates the reflex pupillary dilatation that normally follows noxious stimulation in anesthetized individuals.^[135] The time course of the response appears related to plasma opioid levels, even in the presence of potent inhalation agents.^[136] The changes in pupil size associated with opioid action may be too small to be of clinical utility in assessing the degree of opioid effect.