The brighter the light source the greater the degree of bilateral pupillary constriction. When light is directed into either eye, both pupils react equally. (This is important to understand the pathophysiology of the tonic pupil.) Acetylcholine is released at the neuromuscular junction of the iris sphincter to result in pupillary constriction.ġ2.2.2 Relative Afferent Pupillary Defect The postganglionic parasympathetic fibers innervate the ciliary muscle (for lens accommodation) and the pupillary sphincter muscle (for pupil constriction) in a proportion of 30:1. Parasympathetic fibers for pupillary constriction leave the Edinger–Westphal nucleus and travel along the ipsilateral third cranial nerve to the ipsilateral ciliary ganglion within the orbit. 12.3).Īfferent pupillary fibers leave the optic tract before the lateral geniculate nucleus via the brachium of the superior colliculus to reach the pretectal nuclei (explaining why lesions of the geniculate nucleus, the optic radiations, or the visual cortex do not affect pupillary size or pupillary reactivity, and why lesions of the brachium of the superior colliculus can cause a relative afferent pupillary defect without visual loss).īoth pretectal nuclei receive input from both eyes, and each sends axons to both Edinger–Westphal nuclei (connections are bilateral but predominantly from the contralateral nucleus). Light information from retinal ganglion cells travels through the optic nerves, chiasm (where the nasal fibers decussate), and optic tracts to reach the pretectal nuclei of the dorsal midbrain (▶Fig. When light is shone into one eye, both pupils constrict symmetrically (direct and consensual response to light). Pupillary constriction to light is mediated via parasympathetic (cholinergic) nerve fibers that travel along the third cranial nerve. The information below is from Neuro-ophthalmology Illustrated-2nd Edition. An isolated large pupil without ptosis or diplopia suggests the Adie pupil syndrome or pharmacologic mydriasis.Diplopia, ptosis, and impaired extraocular movements on the side of a large pupil point to a third nerve palsy.A decreased palpebral fissure on the side of a small pupil suggests a Horner syndrome.Determine which pupil is abnormal-the large pupil or the small pupil-by carefully evaluating the pupillary reactions in the dark and in the light.Ģ. Parasympathetic fibers for pupillary constriction leave the Edinger–Westphal nucleus and travel along the ipsilateral third cranial nerve to the ipsilateral ciliary ganglion within the orbit.ġ. This explains why lesions of the geniculate nucleus, the optic radiations, or the visual cortex do not affect pupillary size or pupillary reactivity, and why lesions of the brachium of the superior colliculus can cause a relative afferent pupillary defect without visual loss). The sympathetic fibers responsible for facial sweating and vasodilation branch off at the superior cervical ganglion from the remainder of the oculosympathetic pathway (explaining why patients with a third-order Horner syndrome usually do not have anhidrosis).Īfferent pupillary fibers leave the optic tract before the lateral geniculate nucleus via the brachium of the superior colliculus to reach the pretectal nuclei. It then ascends to the superior cervical ganglion (located near the angle of the mandible and the bifurcation of the common carotid artery). The second-order neuron travels from the sympathetic trunk, through the brachial plexus, and over the lung apex. What specific steps should be followed in examining a patient with anisocoria? What is the ratio of postganglionic parasympathetic fibers that innervate the ciliary muscle to those that innervate the pupillary sphincter muscle?ġ2. What is the course of the parasympathetic fibers for pupillary constriction from the Edinger-Westphal nucleus to the ciliary ganglion?ġ1. Why do lesions of the geniculate nucleus, the optic radiations, or the visual cortex not affect pupillary size or pupillary reactivity?ġ0. What neurotransmitter is released at the neuromuscular junction that results in pupillary dilation?ĩ. What neurotransmitter is released at the neuromuscular junction that results in pupillary constriction?Ĩ. Do patients with a third-order Horner syndrome usually have anhidrosis?ħ. Which order neuron is involved when the Horner syndrome is caused by a tumor in the apex of a lung?Ħ.
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