Pupil Pathway

Summary: • Pupil pathways o Afferent pathway: light in o Efferent pathway: motor response • Classic diagram: eyeballs -> optic nerve -> chiasm o Before geniculate body, pupil fibers come off optic tract, go to dorsal midbrain syndrome • Dorsal membrane centers: o Control pupil efferent pathway o Edinger-Wesphal nucleus of cranial nerve 3 -> carry pathway through postsynaptic postganglionic fiber from ciliary ganglion away from pupil o Afferent signal: retinal ganglion cells in retina -> optic nerve -> temporal fiber (uncrossed) -> nasal fibers (crossed) -> pupil fibers from the optic tract -> pre-tectal nuclei in dorsal midbrain -> efferent pathway of cranial nerve 3 • Detecting afferent pathway problems o Relative afferent pupil defect: > Light reaction of right eye: received at Endinger-Wesphal nucleus level by both pupils • Direct and consensual response to light o Detecting RAPD > Swing light to normal/right pupil: constrict both • Right relative afferent pupillary defect: right and left pupil dilates > RAPD: take advantage of relative different in afferent pathway to pupil • Same bilateral involvement of both eyes o Count finger vision in both eyes due to optic neuropathy -> no RAPD > Bilateral, symmetric > No relative difference between eyes > Light near reaction -> light path impaired > Edinger-Wesphal nucleus: receive signal form more rostral midbrain for near reflex • Note: near reflex also generated when blind > Anterior visual pathway disease -> light near dissociation • Light near association: also in efferent pathway disease o Dissociation occur at dorsal midbrain -> disconnect light pathway from near pathway • Argyll Robertson pupil o Neurosyphilis affects pretectal nuclei area o Lead to light reaction impairment but normal near reaction o Pupil accommodates, does not reacts o Not tonic pupil o Does not react to light, react to near o Light near dissociation > Bilateral, small irregular pupil -> tiny to pinpoint o Efferent pathway deficits of third nerve palsy or the ganglion > From ganglion: idiopathic, also Adie's tonic pupil • Adie's tonic pupil: light near dissociation o Initial same for light near dissociation o Tonic near reaction, constriction stays down o Postganglionic fiber or ganglion disruption: nerve regenerate but afferently > Ciliary body pupil control lens > Near and light reaction poor • Ciliary body not really constricting -> pupil constricting • Due to aberrant regeneration of postganglionic fibers in Adie's tonic pupil o Efferent disease and parasympathetic: anisocoria > Edinger-Wesphal nucleus to ganglion > Postganglionic nerve and iris > More in the Horner syndrome video • Summary: pupil has afferent and efferent pathway o Afferent pathway: test with RAPD and bilateral light near dissociation o Efferent pathway: anisocoria, Horner's pathway (sympathetic or parasympathetics), third nerve, or ganglion in postganglionic nerv