Light Near Dissociation

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Identifier light_near_dissociation_Lee
Title Light Near Dissociation
Subject Dissociation; Ciliary Ganglion; Afferents; Efferents
Creator Andrew G. Lee, MD, Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, TX, Professor of Ophthalmology, Weill Cornell Medicine; A. Claire Chapel, Baylor College of Medicine, Class of 2022
Description Summary: ¬Light near dissociation o Afferent component = retina + optic nerve + chiasm + tract to geniculate body o Efferent component = Edinger-Westphal nucleus + nerve to ciliary ganglion o Light near dissociation -Light pathway is damaged • Light pathway is carried bilaterally on the afferent pathway =Near pathway is intact • For near reaction, both pupils should constrict when light is shone into one eye -Damage to afferent pathway o Optic nerve lesions -no light perception o Near pathway is intact and can still talk to Edinger-Westphal nucleus, ciliary ganglion, and the iris -Light near dissociation will still be produced in blinded eye because efferent pathway is still intact -Bilateral light near dissociation o Bilateral afferent problem o Damage to pretectal nuclei i.e. compressive lesions like pineal tumors or dorsal midbrain syndrome o Near pathway can still communicate with Edinger-Westphal nucleus but light pathway is interrupted o i.e. Argyll Robertson pupil and dorsal midbrain syndrome - Ciliary Ganglion o Damage to the efferent pathway, both light and near reactions will be damaged because they are carried on the same nerve here o However, ciliary ganglion and postganglionic nerve damage and repair itself aberrantly -Fibers that used to go to ciliary body to supply the lens now go to the pupil and cause constriction of the pupil -Light damage intact, near pathway is damaged o i.e. Adie's tonic pupil
Transcript So, one is you can damage the afferent pathway. So, in this example the optic nerve has been damaged and the person has no light perception because there's a lesion in their optic nerve. That means the light pathway will be impaired, but it also means that the near pathway which doesn't require the light can still talk to the Edinger-Westphal nucleus, the ciliary ganglion, and to the iris and so that will produce a light near dissociation in the eye that has been blinded. And if you do it in both eyes, both eyes will be no light perception, but you'll still have a near response. So even if someone's totally blind, no light perception, the pupils can still constrict because the efferent pathway is intact, and that efferent pathway is carried on the third nerve from the Edinger-Westphal nucleus to the ciliary ganglion to the postganglionic nerve. Now in bilateral light near dissociation you can either have a bilateral afferent pathway problem or you can damage the nerve at the pretectal nuclei. So, lesions of the pretectal nuclei by compressive lesions like pineal tumors or the dorsal midbrain syndrome also produce light near dissociation of both pupils because they are affecting the pretectal afferent input to the Edinger-Westphal nucleus. The light pathway will be interrupted at this location, but the near pathway can still talk to Edinger-Westphal nucleus-- and that is a dorsal midbrain type of light near dissociation. And finally, we can have light near dissociation here at the level of the ciliary ganglion, but for an entirely different reason. When you have the ciliary ganglion and the postganglionic nerve damaged it'll regrow and normally it regenerates back to the target, but sometimes it regenerates aberrantly, which means fibers that used to go to the ciliary body to accommodate the lens now are going to the iris and are constricting the pupil. So, in that case the light pathway will be totally intact, but the near pathway might show damage. If you damage the ganglion on the efferent pathway both the light and the near will both be damaged because that's the same nerve. However when it regrows the near pathway might still be able to fire even though the light pathway is damaged and that will produce a different type of light near dissociation: efferent light near dissociation from the postganglionic or the ganglion being damaged with aberrant regenerations leading to the near reaction being intact even though the light reaction is poor. So we can have dissociation between the light and the near pathway on the afferent side, unilaterally or bilaterally, on the pretectal side at the dorsal midbrain connecting to the Edinger-Westphal nucleus, that's Argyll Robertson pupil and the dorsal midbrain syndrome, and at the ganglion and post ganglionic, the most common cause of that is Adie's tonic pupil. And so, you need to know these forms of light near dissociation.
Publisher Spencer S. Eccles Health Sciences Library, University of Utah
Date 2019-10
Format video/mp4
Rights Management Copyright 2019. For further information regarding the rights to this collection, please visit: https://NOVEL.utah.edu/about/copyright
Collection Neuro-ophthalmology Virtual Education Library: NOVEL http://NOVEL.utah.edu
Language eng
ARK ark:/87278/s6ht7dtt
Setname ehsl_novel_lee
Date Created 2019-10-10
Date Modified 2020-01-23
ID 1469303
Reference URL https://collections.lib.utah.edu/ark:/87278/s6ht7dtt
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