What is Being Tested?
Damage anywhere in the visual pathway from the eye to the visual cortex can cause specific deficits in the visual fields of one or both eyes (see Figure 11.15). It is important to note that some visual information from each eye crosses to the opposite side at the optic chiasm. Therefore, lesions in front of the optic chiasm (eye, optic nerve) cause visual deficits in one eye, while lesions behind the optic chiasm (optic tract, thalamus, optic radiations, visual cortex) cause visual field deficits that are similar for both eyes.
Visual hemineglect or extinction is usually caused by contralateral parietal lesions and less often by frontal or thalamic lesions. Neglect is usually more robust in lesions of the right hemisphere (see KCC 19.9).