Vision

Synaptic transmission of impulses from retinal cells follows the optic nerve to the optic chiasma, an x-shaped junction in the brain where half the fibers from each eye cross to the other side of the brain. This means that some visual information from the right half of each retina (from the left visual field) travels to the right visual cortex, and visual information from the left half of each retina (from the right visual field) travels to the left visual cortex. Information from the right half of our environment is processed in the left hemisphere of the brain, and vice versa. Damage to the optic pathway or visual cortex in the left brain—perhaps from a stroke—can cause complete loss of the right visual field. This means only information entering the eye from the left side of our environment is processed, even though information still enters the eye from both visual fields.