Structure and Development of the Optic Chiasm
- Optic nerves of left and right eye meet ventral to the brain
- Left optic nerve crosses over the right one without fusing
- Optic nerves merge in the optic chiasm in vertebrates with large overlap of visual fields
- Partial decussation allows for binocular depth perception
- Optic nerves become optic tracts, which insert on the optic tectum and lateral geniculate body
- Optic nerve crossing guided by cues such as netrin, slit, semaphorin, and ephrin
- Neuronal growth cone responds to cues and induces changes in cytoskeleton
- Retinal ganglion cell axons are blocked by Slit2 and Sema5A inhibition
- RGC axons change from retinotopic to flat sheet-like orientation near the chiasm
- Number of axons that do not cross the midline depends on degree of binocular vision

Function and Evolution of the Optic Chiasm in Different Animals
- Mammals possess optic chiasm, but its evolution is unknown
- Theories proposed for the function of the optic chiasm
- Siamese cats with certain genotypes of albino gene have disrupted wiring
- Optic tracts in cephalopods and insects do not cross the body midline
- Each side of the brain processes the ipsilateral eye in cephalopods and insects

History and Origins of the Optic Chiasm
- Persian physician Esmail Jorjani first identified the crossing of nerve fibers and its impact on vision
- Optic chiasm likely evolved as a consequence of a twist in the early embryo
- Siamese cats with disrupted wiring may compensate with strabismus
- Function of optic chiasm in vertebrates still not fully understood

Studies and Findings Related to the Optic Chiasm
- Semaphorin6D is presented in the optic chiasm
- Plexin-A1 and Nr-CAM are involved in the presentation
- The presentation promotes retinal axon midline crossing
- An ancestral axial twist explains the presence of the optic chiasm in vertebrates
- The axial twist hypothesis predicts opposite asymmetries in different body parts
- Albino cats exhibit abnormal retinotopic organization in the dorsal lateral geniculate nucleus
- The abnormal organization is linked to the absence of tyrosinase
- White tigers have genetic abnormalities in their visual pathways
- The abnormalities affect the visual pathways in the brain
- The cranial nerves have a long history of naming and classification
- The naming of the cranial nerves has evolved over time

Additional Images and Visualizations of the Optic Chiasm
- Scheme showing central connections of optic nerves and tracts
- Brain seen from below with optic chiasm labeled
- Transformations of visual field toward visual map on primary visual cortex
- Brain and brainstem seen from below
- Cerebrum, inferior view, deep dissection

Optic chiasm (Wikipedia)

In neuroanatomy, the optic chiasm, or optic chiasma ( /ɒptɪk kaɪæzəm/; from Greek χίασμα 'crossing', from Ancient Greek χιάζω 'to mark with an X'), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebrates, although in cyclostomes (lampreys and hagfishes), it is located within the brain.

Optic chiasm
Brain viewed from below; the front of the brain is above. Visual pathway with optic chiasm (X shape) is shown in red (image from Andreas Vesalius' Fabrica, 1543).
Optic nerves, chiasm, and optic tracts
Details
System	Visual system
Function	Transmit visual information from the optic nerves to the occipital lobes of the brain
Identifiers
Latin	chiasma opticum
MeSH	D009897
NeuroNames	459
NeuroLex ID	birnlex_1416
TA98	A14.1.08.403
TA2	5668
FMA	62045
Anatomical terms of neuroanatomy [edit on Wikidata]

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)). A midline crossing of nerves inside the brain is called a decussation (see Definition of types of crossings).