These lesions will not affect the near pathway, because it enters the Edinger-Westphal more ventrally. If the lesion is in the dorsal midbrain damaging the pre-tectal nuclei, the light reaction will also be poor bilaterally. If it is a bilateral afferent lesion, both light reactions will be poor with a preserved near reaction. The lesion could either be caused by a bilateral afferent pathway lesion or a lesion of the dorsal midbrain (e.g., pineal tumor, Parinaud syndrome). However, if the postganglionic nerve that previously innervated the iris regenerates aberrantly to the ciliary body, the light reaction will remain poor, but the near reaction would recover, creating an efferent pathway LND. If the lesion is in the efferent pathway, in general both the light and near reactions will be poor at the time of initial injury to the nerve. Bilateral and symmetric afferent defects involving the pupil pathway may not demonstrate an RAPD and LND may be the best demonstration of the bilateral afferent defect. In general, unilateral or bilateral but asymmetric afferent lesions produce a relative afferent pupillary defect (RAPD). If it is in the afferent pathway, the light reaction will be poor, but the near reaction will be spared, because it enters the Edinger-Westphal nucleus in the brainstem ventrally and then proceeds down the efferent pathway with no dependence on the afferent pathway. The lesion could be in either afferent pathway, or it could be in the ciliary body or post-ganglionic nerve. Risk factors for LND are determined by the etiology of the lesion. dorsal midbrain syndrome, Argyll-Robertson pupil, pineal tumor, Wernicke’s encephalopathy), or a lesion in the efferent pathway (e.g., ciliary ganglion, post-ganglionic nerve) with subsequent aberrant regeneration. ![]() LND may result from a lesion in the afferent pupillary pathway (e.g., retinal ganglion cells, optic nerve, chiasm, tract, lateral geniculate body), a pretectal lesion (e.g. This article will discuss the causes and implications of LND. The afferent pathway is more commonly affected (disrupting the light response) as a cause of LND but the efferent pathway can also be affected in a lesion of the ciliary ganglion or postganglionic nerve with subsequent aberrant regeneration. ![]() This is clinically significant, because since the efferent pathway is shared for both reactions, there are limited mechanisms for the dissociation of the two pathways. LND can occur unilaterally or bilaterally. Light-near dissociation (LND) is a pupillary sign that occurs when the pupillary light reaction is impaired while the near reaction (accommodative response) remains intact.
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