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Optic chiasma

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Visual pathway with optic chiasm (X shape outlined, red. Brain seen from underneath.
Scheme showing central connections of the optic nerves and optic tracts.

The optic chiasma, or 'optic chiasm',[1] 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.[2]


The images on the nasal (inner) sides of each retina cross over to the opposite side of the brain via the optic nerve at the optic chiasm. The temporal (outer) images, on the other hand, stay on the same side. This allows the images from either side of the visual field to go to the appropriate side of the brain, combining the sides together.

Beyond the optic chiasm, with crossed and uncrossed fibers, optic nerves become optic tracts.

This system 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.[3]


  1. Greek χίασμα, "crossing", from the Greek χιαζω 'to mark with an X', after the Greek letter 'Χ', chi
  2. Colman, Andrew M. 2006. Oxford Dictionary of Psychology. 2nd ed, Oxford University Press. p530 ISBN 0198610351
  3. Eye, human. Encyclopædia Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2009