Bilateral altitudinal visual fields.

We describe two patients with absolute, complete, binocular inferior altitudinal hemianopias. These altitudinal visual-field defects (AVFDs) involved both nasal and adjacent temporal quadrants and respected the horizontal meridian. The reported conditions and locations in the visual system that cause "conventional" AVFDs and their bilateral occurrence are reviewed. Division of the visual system into altitudinal halves results from the topographic arrangement of nerve fibers and their blood supply in the retina, optic nerves, and visual cortex. Lesions at these locations resulting in AVFDs are usually due to vascular occlusion or may result from a penetrating missile injury to the superior occipital lobes. It is important to emphasize that the nerve fiber layer of the retina respects the horizontal meridian only in the nasal field, not in the temporal field; therefore incomplete AVFD is more common. Because of the anastomotic blood supply of the occipital pole, only AVFDs due to occipital infarcts spare fixation. Diagnosis of retinal branch artery occlusion or anterior ischemic optic neuropathy is aided by the presence of a unilateral AVFD along with ipsilateral funduscopic abnormalities and, in most bilateral examples, by its sequential temporal development. Bilateral occipital infarcts, as in our two cases, are characterized by sudden, simultaneous onset of AVFDs, an absence of retinal, retinovascular, or optic nerve abnormality and confirmation by computed tomographic scanning.