![]() ![]() Impulses from the temporal half of retina travel via the ipsilateral optic tract to reach the ipsilateral pretectal nucleus. Impulses from the nasal half of retina decussate in the optic chiasm and pass via contralateral optic tract to reach the contralateral pretectal nucleus. First (sensory afferents) connects each retina with both pretectal nuclei located in midbrain at the level of the superior colliculus.The light reflex is mediated by retinal photoreceptors and subserved by four neurons. This response in the contralateral eye is known as a consensual light reflex. Simultaneously, the pupil of the other eye also constricts. This pupillary constriction is known as a direct light reflex. When a bright light is shone on one eye, its pupil constricts. This occurrence of RAPD was justified due to the inaccuracy of measurement or synaptic asymmetries of the visual pathway.Īn RAPD is noted in more than 90% of cases of acute unilateral cases of optic neuritis, 91% cases of ischemic central retinal vein occlusion (CRVO), more than 50% cases of retinal detachment involving the macula, and 23% cases of primary open-angle glaucoma (POAG). In a study conducted using binocular pupilometer, 42% of the normal population showed an RAPD between 0.08 and 0.22 log units, and 6% had an RAPD between 0.23 and 0.39 log units. There is no specific age and sex predilection for Marcus Gunn pupil in isolation. RAPD will be induced in the smaller pupil when anisocoria is greater than 2 mm. Lesions of the optic tract, pretectum, dense cataract, and eye patching/dark adaptation produce RAPD in the contralateral eye. Amblyopia - may not be clinically appreciable.Dense cataract (see following discussion).Central serous chorioretinopathy (CSCR)- may not be clinically appreciable.Central retinal vein occlusion (CRVO).Lesions of the Optic Nerve and Visual Pathway All the causes may not cause clinically appreciable RAPD. The relative afferent pupillary defect is seen in various disorders (see pathophysiology). Dilatation of pupils of both eyes when the light stimulus is rapidly transferred from the normal eye (after brief light exposure to the normal eye) to the affected eye. Constriction of pupils of both eyes when the light stimulus is applied to the normal eyeĢ.The presence of a relative afferent pupil defect (RAPD) is the hallmark of a unilateral afferent sensory abnormality or bilateral asymmetric visual loss.Īn afferent pupillary response is characterized by: Hirschberg first noted this phenomenon in the case of unilateral retrobulbar optic neuritis. It is named after Scottish Ophthalmologist Robert Marcus Gunn. A Marcus Gunn pupil, on the other hand, has a relative weakness of the afferent limb of the pupillary light reflex compared to the other eye because of which when light is rapidly transferred from the normal eye to the eye with MGP, the MGP dilates instead of constricting. After exposure to bright light, a normal pupil constricts. In literature, the term is often used synonymously with Marcus Gunn phenomenon or relative afferent pupillary defect (RAPD). Marcus Gunn pupil (MGP) is the term given to an abnormal pupil showing aberrant pupillary response in certain ocular disorders. Outline the prognosis and interprofessional care of patients with Marcus Gunn pupil.Review the evaluation process of patients with Marcus Gunn pupil.Summarize the relevant history and physical examination of patients with Marcus Gunn pupil.Describe the etiology, epidemiology, and pathogenesis of Marcus Gunn pupil.This activity reviews the evaluation of Marcus Gunn pupil and highlights the role of the interprofessional team in evaluating and treating patients with this condition. To avoid the high morbidity associated with this condition, it must be promptly diagnosed and the cause should be treated. Marcus Gunn pupil is indicative of a defect in the afferent pathway of the light reflex. ![]()
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