Optic radiation

Brain: Optic radiation
Colour coded diagram showing radiations in quadrants from retinal disc through the brain
Latin	radiatio optica
NeuroNames	ancil-529

The optic radiation (also known as the geniculo-calcarine tract or as the geniculostriate pathway) is a collection of axons from relay neurons in the lateral geniculate nucleus of the thalamus carrying visual information to the visual cortex (also called striate cortex) along the calcarine fissure.

There is one such tract on each side of the brain.

Parts

A distinctive feature of the optic radiations is that they split into two parts on each side:

Source	Path	Information	Damage
Fibers from the inferior retina (also called "Meyer's loop" or "Archambault's loop")	must pass through the temporal lobe by looping around the inferior horn of the lateral ventricle.	Carry information from the superior part of the visual field	A lesion in the temporal lobe that results in damage to Meyer's loop causes a characteristic loss of vision in a superior quadrant (quadrantanopia.)
Fibers from the superior retina (also called "Baum's loop")	travel straight back through the parietal lobe to the occipital lobe in the retrolenticular limb of the internal capsule to the visual cortex.	Carry information from the inferior part of the visual field	Taking the shorter path, these fibers are less susceptible to damage.

Right superior quadrantanopia. The areas of the visual field lost in each eye are shown as black areas. This visual field defect is characteristic of damage to Meyer's loop on the left side of the brain.

Additional images

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  Horizontal section of right cerebral hemisphere.

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  Diagram of the tracts in the internal capsule.

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  3D schematic representation of optic tracts

External links

• Optic+radiation at eMedicine Dictionary
• Kier LE, Staib LH, Davis, LM, Bronen, RA (1 May 2004). "MR Imaging of the Temporal Stem: Anatomic Dissection Tractography of the Uncinate Fasciculus, Inferior Occipitofrontal Fasciculus, and Meyer’s Loop of the Optic Radiation". Am J Neuroradiology 25 (5): 677–691. PMID 15140705. http://www.ajnr.org/cgi/content/abstract/25/5/677. Retrieved 2007-12-19. 
• http://www2.umdnj.edu/~neuro/studyaid/Practical2000/Q34.htm