Optic radiation

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Deep dissection of cortex and brain-stem. (Optic radiation labeled at center left.)

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.

The geniculo-calcarine tract, also known as the optic radiation, 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.

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

• The fibers from the inferior retina must pass into the temporal lobe by looping around the inferior horn of the lateral ventricle. These fibers, which carry information from the superior part of the visual field, are called Meyer's loop or Archambault's loop. A lesion in the temporal lobe that results in damage to Meyer's loop causes a characteristic loss of vision in a superior quadrant.

• The fibers from the superior retina travel straight back to the occipital lobe in the retrolenticular limb of the internal capsule to the visual cortex. They carry information from the inferior part of the visual field and, taking the shorter path, are less susceptible to damage.

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