Anatomy of the visual pathways.

The axons of the retinal ganglion cells form the optic nerve. The two optic nerves meet at the optic chiasm, where the nerve fibers originating in the nasal retina of each eye decussate to join the temporal fibers of the fellow eye. From the chiasm, the same axons continue on as the optic tract. These axons travel to and synapse in the lateral geniculate nucleus, the cells of which send their axons through the optic radiations to the visual cortex. The main blood supply to visual cortex is provided by the posterior cerebral arteries and their branches (the calcarine, posterior temporal, and parieto-occipital arteries). At the occipital pole, however, there may be a dual blood supply to the area subserving central vision, with anastomoses between branches of the posterior cerebral arteries and the superior temporo-occipital branch from the middle cerebral artery.