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Optic Radiations and the Visual Pathway

Surgical Correlation

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Optic radiations and visual pathway.  This ventral dissection of a whole brain demonstrates the CNS visual pathway from optic chiasm to optic radiation.  The two optic nerves converge at midline to form the optic chiasm.  Here, the fibers undergo a partial decussation with the net result that visual information from one hemifield enters the contralateral optic tract. The optic tract runs caudally along the lateral surfaces of the hypothalamus and cerebral peduncle to terminate in the lateral geniculate nucleus (LGN) of the thalamus, located on the ventral surface of the pulvinar.  Axons of LGN neurons form the optic radiation and convey visual information to the primary visual cortex.  The optic radiation is visuotopically organized: fibers carrying information from the inferior half of the visual field travel in the superior part of the optic radiation, whereas fibers carrying information from the superior half of the visual field travel in the inferior part of the optic radition.  The latter fibers, as seen in this dissection, extend anteriorly (distance A – B) around the temporal horn of the lateral ventricle within Meyer's loop, then loop posteriorly to course along the lateral wall of the temporal horn and atrium to reach the primary visual cortex. The arrow on the right side of the image indicates the anterior tip of Meyer's loop.  The distance from the tip of Meyer's loop to the temporal pole has been reported to range from 25-47mm (mean= 35mm) (Image courtesy of PA Rubino)

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