The optic nerves serving the eyes join behind the eyes just in front of the pituitary gland to form a cross-shaped structure called the optic chiasma.
Within the optic chiasma some of the nerve fibers cross. The fibers from the nasal (inside) half of each retina cross over, but those from the temporal (outside) sides do not. Specifically, fibers from the nasal half of the left eye and the temporal half of the right eye form the right optic tract; and the fibers from the nasal half of the right eye and the temporal half of the left form the left optic tract.
The nerve fibers then continue along in the optic tracts. Just before they reach the thalamus of the brain, a few of the nerve fibers leave to enter nerve nuclei that function in visual reflexes.
Most of the nerve fibers enter the thalamus and form a junction (a synapse) in the back of the thalamus. From there the visual impulses enter nerve pathways called the optic radiations which lead to the visual (sight) cortex of the occipital (back) lobes of the brain.
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