[Visual defect due to chiasmic compression by the A1 portion of the anterior cerebral artery].

Unilateral nasal hemianopia is highly difficult to notice with bilateral vision intact, and only a few cases has been reported. There are several reported cases of quadrantic hemianopsia caused by cerebral lesions, but the defects were found bilaterally in all cases. There is only one reported case of which an aneurysm was believed to be the cause. We confronted 3 cases of unilateral nasal quadrantic hemianopia. In either case no ophthalmologic disorders could be found but magnetic resonance imaging revealed the compression of the optic chiasma by the A1 portion of the anterior cerebral artery. All three cases are presently under conservative therapy and receive routine evaluations. Nerve fibers from the upper and lower areas of the retina are routed complicatedly in the optic nerve in the periphery of the optic chiasma. From the presentation of the quadrantic hemianopia and from the radiological findings, we diagnosed that the visual defect was caused by vascular compression of the optic chiasma.