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The optic chiasm is found in all vertebrates, although in cyclostomes (lampreys and hagfishes), it is located within the brain. [2] [3] This article is about the optic chiasm of vertebrates, which is the best known nerve chiasm, but not every chiasm denotes a crossing of the body midline (e.g., in some invertebrates, see Chiasm (anatomy)).
The opening of each optic canal is placed at either lateral end of the chiasmatic sulcus. The optic chiasm is situated superior and quite posterior to the chiasmatic groove (and not against the groove as the name suggests). [2]: 509 Chiasmatic groove
Optic gliomas are usually pilocytic tumors, and can involve the optic nerve or optic chiasm. [3] Optic gliomas are usually associated with neurofibromatosis type 1 in 30% of people with the condition. [3] Optic nerve gliomas have low mortality but extremely high prevalence of vision loss and eye-bulging exophthalmos) in children. [4]
Chiasms are found in vertebrates but also in invertebrates. The optic chiasm in vertebrates can be of type I or II. [1] [4] However, an optic chiasm of type III is found in many insects [2] and in cephalopods. [3] In vertebrates, three of the cranial nerves show a chiasm. The optic chiasm of the optic tract (type I or II)
The second most common initial manifestation of the disease is inflammation of the optic nerve and/or optic chiasm (optic neuritis, ON). [4] ON may lead to varying degrees of visual impairment with decreased visual acuity , although visual field defects, or loss of color vision , may occur in isolation or prior to formal loss of visual acuity.
It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and superior colliculus. [ 1 ] It is composed of two individual tracts, the left optic tract and the right optic tract, each of which conveys visual information exclusive to its respective ...
The optic tract grows from the retina to the optic tectum. Because dorsal and ventral are inverted in the anterior head region, the tracts grow at first toward the ventral side, to meet in the midline to form a chiasma. Since the optic tectum lies on the dorsal midbrain, each tract then continues dorsally to the contralateral optic tectum. [10]
The LGN receives information directly from the ascending retinal ganglion cells via the optic tract and from the reticular activating system. Neurons of the LGN send their axons through the optic radiation, a direct pathway to the primary visual cortex. In addition, the LGN receives many strong feedback connections from the primary visual ...