Optic Chiasm and Tract

The nerve fibers from the retinal ganglion cells in each eye travel through the chiasm and the optic tract before synapsing at the lateral geniculate nuclei. In the optic chiasm, the fibers originating from the nasal part of the retina of each eye decussate, whereas the temporal fibers pass through uncrossed. The optic tract on each side contains crossed nasal retinal fibers from the opposite eye and the uncrossed temporal fibers from the same eye. As a result, lesions of this region involving these two structures produce characteristic defects of the visual field that can help in diagnosing the disease.