Editing Optic chiasm (section)

==Structure==

[[File:Optical-transformations.png|300px|thumb|'''Figure 2''' Transformations of the visual field toward the visual map on the primary visual cortex in vertebrates.  U=up; D=down; L=left; R=right; F=fovea]]
{{Main|Chiasm (anatomy)#Structure}}

In all vertebrates, the optic nerves of the left and the right eye meet in the body midline, ventral to the brain. In many vertebrates the left optic nerve crosses over the right one without fusing with it.<ref name="Polyak1957">{{cite book
|location = Chicago
|first=Polyak|last=Stephen
|publisher = Chicago Univ. Press
|title = The vertebrate visual system
|date=1957}}</ref>

In vertebrates with a large overlap of the visual fields of the two eyes, i.e., most mammals and birds, but also [[amphibians]], [[reptile]]s such as [[chameleons]], the two optic nerves merge in the optic chiasm. In such a merged optic chiasm, part of the nerve fibres do not cross the midline, but continue towards the [[optic tract]] of the ipsilateral side. By this partial decussation, the part of the [[visual field]] that is covered by both eyes is fused so that the processing of binocular [[depth perception]] by [[stereopsis]] is enabled (see Figure 2).

In the case of such partial decussation, the optic nerve fibres on the medial sides of each [[retina]] (which correspond to the lateral side of each visual hemifield, because the image is inverted) cross over to the opposite side of the body midline. The inferonasal retina are related to the anterior portion of the optic chiasm whereas superonasal retinal fibers are related to the posterior portion of the optic chiasm.

The partial crossing over of optic nerve fibres at the optic chiasm allows the visual cortex to receive the same hemispheric [[visual field]] from both eyes. Superimposing and processing these monocular visual signals allow the visual cortex to generate [[Binocular vision|binocular]] and [[Stereopsis|stereoscopic]] vision. The net result is that the right cerebral hemisphere processes left visual hemifield, and the left cerebral hemisphere processes the right visual hemifield.

Beyond the optic chiasm, with crossed and uncrossed fibers, the optic nerves are called [[optic tracts]]. The optic tract inserts on the [[optic tectum]] (in [[mammals]] known as [[superior colliculus]]) of the [[midbrain]]. In mammals they also branch off to the [[lateral geniculate body]] of the [[thalamus]], in turn giving them to the occipital cortex of the [[cerebrum]].<ref name="Nieuwenhuys1998">{{cite book
|last1=Nieuwenhuys|first1=R.
|last2=Donkelaar|first2=H.J.
|last3=Nicholson|first3=C.
|last4=Smeets|first4=W.J.A.J.
|last5=Wicht|first5=H.
|title=The central nervous system of vertebrates.
|date=1998
|publisher=Springer
|location=New York
|url=https://www.springer.com/us/book/9783540560135
|isbn=9783642621277}}</ref>

=== Arterial supply ===
The optic chiasma receives its arterial supply from the [[Anterior cerebral artery|anterior cerebral arteries]], and from branches of the [[internal carotid artery]] which ascend along the [[pituitary stalk]] (the latter supplying the midline portion of the chiasma).<ref name=":2242">{{Cite book |last=Standring |first=Susan |url=https://www.worldcat.org/oclc/1201341621 |title=Gray's Anatomy: The Anatomical Basis of Clinical Practice |publisher=[[Elsevier]] |year=2020 |isbn=978-0-7020-7707-4 |edition=42th |location=New York |pages=420 |oclc=1201341621}}</ref>