This chapter discusses cortical visual defects in terms of primary deficits in visual field loss from damage to the geniculostriate pathway, and secondary deficits from damage to components of the ventral and dorsal streams. Incomplete bilateral hemianopia can be distinguished from bilateral ocular disease by the congruity of the visual loss and usually a step defect along the vertical meridian, the best clue to the hemifield nature of the loss. Bilateral lesions in the posterior portions of the cerebral hemispheres, including the occipital lobes, the posterior temporal lobes, and the inferior posterior parietal lobes, are surprisingly common. Astereopsis occurs in patients with bilateral occipitoparietal lesions. Less severe deficits occur with unilateral lesions. Other visuospatial dysfunction may be associated. Stereotests, which are cards viewed with different polarized or colored glasses worn by the two eyes, are required to measure deficient stereopsis.