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Brain: Optic chiasm
Visual pathway with optic chiasm (X shape outlined, red) (1543 image from Andreas Vesalius' Fabrica)
Latin chiasma opticum
Gray's subject #197 883
MeSH Optic+chiasm
NeuroLex ID birnlex_1416

The optic chiasm or optic chiasma (Greek χίασμα, "crossing", from the Greek χιαζω 'to mark with an X', after the Greek letter 'Χ', chi) is the part of the brain where the optic nerves (CN II) partially cross. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus.[1]



Specifically, in the optic chiasm, the nerves connected to the right eye that attend to the left temporal visual field (located in the right retina) remain on the right (ipsilateral) side of the brain, and the nerves from the left eye that attend to the right temporal visual field (located in the left retina) remain on the left (ipsilateral) half of the brain.

This allows for parts of both eyes that attend to the right visual field to be processed in the left visual system in the brain, and vice versa.

Optic chiasm in cats

In Siamese cats with certain genotypes of the albino gene, this wiring is disrupted, with less of the nerve-crossing than is normal, as a number of scholars have reported. [2] To compensate for lack of crossing in their brains, they cross their eyes (strabismus). [3]

This is also seen in albino tigers, as Guillery & Kaas report.[4]

Additional images

See also


  1. ^ Colman, Andrew M. (2006), Oxford Dictionary of Psychology (2nd ed.), Oxford University Press, p. 530, ISBN 0198610351  
  2. ^ OMIA "Coat colour, albinism. Phenotype in cat (Felis catus)." (in English). OMIA. OMIA. Retrieved 2009-09-26.  
  3. ^ Guillery RW, Kaas JH (June 1973). "Genetic abnormality of the visual pathways in a "white" tiger". Science 180 (92): 1287–9. PMID 4707916.  
  4. ^ Guillery RW (May 1974). "Visual pathways in albinos". Sci. Am. 230 (5): 44–54. PMID 4822986.  

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