Pupillary response

• Pupilloconstrictor (parasympathetic) fibers arise in the Edinger-Westphal nucleus in the high midbrain; the pupillodilator (sympathetic) fibers aris in the posterolateral part of the hypothalamus and descend, uncrossed, in the lateral tegmentum of the midbrain, pons, medulla, and cervical spinal cord to the eight cervical and first and second throracic segments which synapse with the lateral horn cells; the latter cells give rise to the preganglionic fibers, most of which leave the cord by the second ventral thoracic root and proceed through to the stellate ganglion and synapse in the superior cervical ganglion; the postganglionic fibers course along the internal carotid artery and traverse the cavernous sinus where they join the first division of the trigeminal nerve, finally reaching the eye as the long ciliary nerve
• Pathway for the pupillary light reflex is retinal receptor cells, through bipolar cells, synapsing on retinal ganglion cells with axons of those cells running in the optic nerve and tract; light reflex fibers leave the optic tract just rostral to the lateral geniculate body and enter the high midbrain where they synapse in the pretectal nucleus; intercalated neurons give rise to the pupillary motor fibers which pass to the ipsilateral and contralateral Edinger-Westphal nucleus
  • Gunn pupillary sign – slowness of response along with failure to sustain pupillary constriction; seen in damaged retina or optic nerve
  • Gunn “jaw winking” – ptotic eyelid retracts momentarily when the mouth is opened or the jaw is moved to one side
    • inverse Marcus Gunn phenomenon – ptosis occurring with opening of the mouth
    • both due to abnormalilties in central connections to the levator and pterygoid muscles
  • atropine – dilates pupils; also epinephrine and cocaine dilate pupils
  • physostigmine constrict pupils (stimulates sphincter muscle) as does pilocarpine (muscarinic agonist); morphine and narcotics also constrict pupils
  • Argyll Robertson pupil – failure to react to light but constrict on accommodation; seen in syphilis, Lyme disease, pinealoma, MS, occasionally diabetes
  • Adie’s pupil – due to degeneration of ciliary ganglia of parasympathetic fibers; reaction to light is greatly reduced; pupil responds better to near than to light; once the pupil constricts to near it dilates very slowly; pupil is usually sensitive to .1% pilocarpine; more common in women