New York: Oxford University Press 2001.)Ģ. Efferent pupillomotor impulses travel in the parasympathetic fibers of the oculomotor nerve, synapse in the ciliary ganglion of the orbit, and then pass via the short ciliary nerves to innervate the iris sphincter muscle. The neurons of the Edinger–Westphal subnucleus initiate the efferent limb of the pupillary light reflex, that is, pupilloconstriction. Each pretectal olivary nucleus distributes the afferent pupillary impulses to the ipsilateral and contralateral Edinger–Westphal subnucleus of the oculomotor nuclear complex. Pupillary information is conveyed from the eye to the brain by the melanopsin-expressing retinal ganglion cells and their axons project to the dorsal midbrain, synapsing in the pretectal olivary nucleus. The afferent limb originates in the retinal photoreceptors that convert light energy to a neural signal. The amplitude and velocity of pupillary constriction as well as the degree of redilation that occurs within the 3 seconds of light stimulation should be symmetric between the 2 eyes.įIGURE 11.1 Schematic diagram of the pupillary light reflex. Repeat this for 4 or 5 alternations of light stimulation and watch only the illuminated pupil (direct light response). ![]() ![]() Shine a bright focal light directly onto 1 pupil for 3 seconds, then quickly swing the light onto the other pupil for 3 seconds. ![]() Technique. Have the patient fixate a distant target in a dark room. Alternating light test. This is the standard clinical technique for identifying asymmetry of afferent pupillomotor input between the 2 eyes, referred to as the relative afferent pupillary defect ( RAPD).The patient usually has subnormal vision in the eye with an RAPD.ġ. Proceed to the alternating light test to distinguish an afferent pupil defect and check the pupil near response, which should be equally sluggish in the event of an efferent defect.ĭ. Do this for each pupil 2 or 3 times for a mental “average.” Reminder: Simply noting that a pupil is “sluggish” or “responds poorly” to direct light stimulation is not enough information to differentiate an afferent from an efferent pupillary defect. Shine a bright focal light (a nonhalogen penlight is not bright enough) directly onto 1 pupil for 3 seconds and record the amplitude and velocity of constriction. Pupillary response to light. Have the patient fixate on a distant target in a darkened room. When present, anisocoria should be measured in darkness and under bright light.ġ. Anisocoria that is greater in magnitude under bright light implies a deficit of constriction, thus, the larger pupil is faulty.Ģ. Anisocoria that is more apparent in darkness or dim light implies a failure of dilation, thus, the smaller pupil is faulty.Ĭ. Asymmetry of pupil size of 0.4 mm or more is visible to the unaided eye and called anisocoria. Pupil size. Resting pupil size is greatest during the teenage years and then gradually decreases with increasing age. Hippus. An awake patient sitting quietly in room light may show small spontaneous oscillations of pupil size, known as hippus. It reflects fluctuations in the modulating signals to the Edinger–Westphal subnuclei.ī. The pupil size at any moment is determined by the sum input of sympathetic and parasympathetic activity to two iris muscles, the radial dilator, and the sphincter.Ī. Pupillary dilation is a reflex response to sudden arousal or darkness and is mediated by the sympathetic pathway ( Fig. (See the section on Unilateral Mydriasis.) Injury along the efferent limb causes mydriasis of the ipsilateral pupil and poor pupillary constriction to all forms of stimulation-direct light, consensual light, or near effort. Except at the brachium of the superior colliculus and pretectal olivary nucleus, injury along the afferent limb of the pupil light reflex also results in some form of accompanying visual loss and in unilateral or asymmetric bilateral lesions, a relative afferent pupillary defect (RAPD) will be detected.The efferent limb of the pupil light reflex carries pupilloconstriction signals originating in the Edinger–Westphal subnucleus to the iris. The afferent limb signals pupillomotor information from the retina to the dorsal midbrain. The pupillary light reflex is composed of an afferent limb and an efferent limb ( Fig. Approach to the Patient with Abnormal Pupils
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