![]() ![]() Pupillary light reflex-parasympathetic pathway. The ipRGCs are most sensitive to blue light, and the preservation of circadian rhythms and the pupillary light reflexes in patients with severe photoreceptor diseases and Leber’s hereditary optic neuropathy can be explained by intact ipRGC function. Additionally, intrinsically photosensitive retinal ganglion cells (ipRGCs) containing melanopsin, a photopigment, can be activated by light without photoreceptor input. Light entering the eye causes retinal photoreceptors to hyperpolarize, in turn causing activation of retinal interneurons and ultimately the retinal ganglion cells. Normally, light directed at either eye leads to bilateral pupillary constriction, and this pupillary light reflex is mediated by a parasympathetic pathway (see Fig. The sphincter muscle wraps 360 degrees around the pupillary margin, and the dilator muscle similarly encircles the pupil but is more peripherally located. Contraction of the dilator muscle leads to pupillary enlargement (mydriasis), while sphincter muscle contraction causes pupillary constriction (miosis). The iris contains the two muscles that control the size of the pupil. Note the pupil is slightly nasal to the center of the cornea and iris. However, there are no eyelid or movement abnormalities.A normal left eye. Balcer explained, and in the early course patients may complain of accommodative insufficiency or glare. ![]() However, they exhibit light-near dissociation, Dr. Tonic pupilsPatients with tonic pupils often notice one large or irregular pupil, which tends to become miotic when the condition is chronic. "When a patient with aberrant regeneration of the third nerve presents, the ophthalmologist should think of compressive lesions, most often aneurysms or tumors," she emphasized. Balcer demonstrated.Ĭompressive lesions and trauma are the most common causes of aberrant regeneration of the third nerve. The pupil did not react to consensual light stimulation however, upon adduction the pupil became more miotic than that of the left eye, Dr. This recovered into a partial pupil involving third nerve palsy. She described a patient with pituitary apoplexy who had complete ophthalmoplegia of the right eye. ![]() As they regrow, they reach the ciliary ganglion and result in miosis when the patient adducts the eye, according to Dr. Many different types of this pathology have been identified, but in the case of light-near dissociation, the fibers that used to innervate the medial or inferior rectus muscle of the third nerve are damaged. She described a patient with Argyll-Robertson pupils who was shown to have pupils that did not respond well to light but contracted to near.Īberrant regenerationWhen patients present with unilateral light-near dissociation, eye movement abnormalities, or signs of a third nerve palsy, there may be aberrant regeneration. This also spares the supranuclear fibers that subserve the pupillary near response," she said. "The lesion is thought to occur within the interneurons that connect the pretectal nuclei and the Edinger-Westphal nuclei in the midbrain. ![]() Unlike the pupils of dorsal midbrain syndrome, Argyll-Robertson pupils also may be irregular and dilate poorly in the dark. Balcer noted that Argyll-Robertson pupils, which are miotic, are classically associated with neurosyphilis. Midbrain abnormalities that cause light-near dissociation are often bilateral, but they can be unilateral or asymmetric.Īrgyll-Robertson pupilsArgyll-Robertson pupils are another prominent cause of bilateral pupillary light-near dissociation. The pupils in the dorsal midbrain syndrome are midposition or large," she said. "The most common lesions in this case are those caused by hydrocephalus, stroke, or tumor. The result is pupillary light-near dissociation," she said. A lesion in this region spares the supranuclear fibers that descend directly toward the ocular motor nerve complex. "The lesion in these patients is located in the pretectal nuclei and ganglion cell axons as they enter the midbrain. Balcer, as well as upgaze paresis, convergence retraction nystag- mus, and eyelid retraction. Dorsal midbrain syndromeIn patients with dorsal midbrain syndrome, light-near dissociation is a prominent feature, according to Dr. ![]()
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