![]() The impulses travel through the optic nerve (CN II), which projects bilaterally to the pretectal nucleus in the midbrain, and then projects to the Edinger-Westphal nucleus. Light stimulates the retinal ganglionic cells. The optic nerve directs the afferent limb of the reflex pathway. The parasympathetic system constricts the pupil to protect itself when light intensity increases to an uncomfortable level by decreasing the amount of light entering the eye. Pupillary Light Reflex Pathway (parasympathetic innervation pathway) The majority of the fibers pass posteriorly to become the genico-calcarine tracts, which have both parietal and temporal loops in the form of the dorsal optic radiation and Meyer's loop and terminate into the cuneus gyrus and lingual gyrus of the primary visual cortex, respectively (Broadmann area number 17). The optic tract then passes posteriorly where most of the axons synapse in the layers of the lateral geniculate body (LGB) of the midbrain, which is a posterolateral extension of the thalamus with a minority passing into the superior colliculus and Edinger-Westphal nuclei these fibers allow for parasympathetic innervation of the pupil, i.e., pupillary constriction. This anomaly helps eye healthcare professionals in the assessment of the site of the lesion along the visual pathway, which produces well-described visual field defects, also known as hemianopias, posterior, or at the chiasm.īeyond the chiasm, the pathway continues as two distinct tracts, each carrying the temporal fibers from the other eye. Here more than half of the nasal fibers from the left eye decussate to join the temporal fibers of the right eye and form the right optic tract and vice versa. This continues till the two optic nerves join together to form the optic chiasm directly behind and above the pituitary stalk. It exits into the middle cranial fossa to form the intracranial part of the optic nerve. It then enters the optic canal, a bone-encased tunnel intended to protect the nerve. The axons exit the orbit through the orbital foramen, simultaneously with the ophthalmic artery and sympathetic fibers. The nerve is surrounded by the dura, which is in continuation of that of the brain, allowing free movement of CSF between the eye and the intracranial vault. These fibers join together at the optic disc and are redirected posteriorly out of the eye to form the orbital part of the optic nerve. It consists of two types of fibers, namely temporal and nasal fibers, which control the nasal and temporal parts of the visual field, respectively. The ganglion cell layer and nerve fiber layer serve as the foundation of the optic nerve the former contains the cell bodies, and the latter contains the axons as they stream across the retina. The photoreceptor layers consist of the rods and cones, which generate action potentials with the help of rhodopsin through photosensitive cycles. The optic pathway begins in the retina, which is a complex structure made up of ten different layers. 1856 10:170–93.The visual system consists of two primary parallel pathways: an optic pathway and a pupillary reflex pathway. Zur pathologischen anatomic der netzaut und des scherven. Syndrome of myelinated retinal nerve fibers, myopia, and amblyopia: a review. Tarabishy AB, Alexandrou TJ, Traboulsi EI. Straatsma BR, Foos RY, Heckenlively JR, Taylor GN. Characteristics of myelinated retinal nerve fiber layer in ophthalmic imaging: findings on autofluorescence, fluorescein angiographic, infrared, optical coherence tomographic, and red-free images. Shelton JB, Digre KB, Gilman J, Warner JEA, Katz BJ. Acquired retinal myelination in neurofibromatosis 1. Development of myelin in human optic nerve and tract: a light and electron microscopic study. Myelinated retinal nerve fibers: prevalence, location and effect on visual acuity. Acquired and progressive retinal nerve fiber layer myelination in an adolescent. Jean-Louis G, Katz BJ, Digre KB, Warner JEA, Creger DD. The relation of the blind spot to medullated nerve fibers in the retina. Morphological consequences of myelination in the human retina. A sign of multiple basal cell nevi (Gorlin’s) syndrome. 2013 161(4):829–34.ĭe Jong PT, Bistervels B, Cosgrove J, de Grip G, Leys A, Goffin M. GAPO syndrome: four new patients with congenital glaucoma and myelinated retinal nerve fiber layer. Progression of retinal nerve fiber myelination in childhood. 1985 103:542–4.Īli BH, Logani S, Kozlov KL, Arnold AC, Bateman B. Acquired and progressive myelinated nerve fibers.
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