Visual Nerve Pathways

The axons and ganglion cells in the retina leave the eyes to form the "optic nerves." Just in front of the pituitary gland, these nerves form the X-shaped "optic chiasma," and within the chiasma some of the fibers cross over. The fibers from the nasal half of each retina cross over, but those from the temporal 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 in the optic tracts. Just before they reach the thalamus, a few of them leave to enter nuclei that function in various visual reflexes. Most of the fibers, however, enter the thalamus and form a junction (synapse) in the back of it. From this region the visual impulses enter nerve pathways called "optic radiations," which lead to the visual cortex of the occipital lobes of the brain.