There are four classic types of visual field defects. Altitudinal field defects in which the defect is present above or below the horizontal midline are usually associated with ocular abnormalities. A central scotoma is characteristic of optic nerve disease of macular disease. A bitemporal hemianopia signifies optic chiasm disease and is most frequently associated with pituitary tumors. With homonymous hemianopia, the same portion of the field is absent in both eyes, and is found with lesions behind the chiasm.