Walsh & Hoyt: Neuro-Ophthalmologic Signs Associated with Optic Chiasmal Syndromes

Patients with chiasmal syndromes may or may not have ophthalmoscopically apparent nerve fiber layer or optic atrophy when first examined. However, when atrophy is present in patients with bitemporal hemianopia, its pattern is quite specific, appearing as a band across the disc (i.e., ""band atrophy""). The reason for this is that degeneration occurs in fibers from peripheral and macular retinal ganglion cells located nasal to the fovea. Axons from peripheral retinal ganglion cells located nasal to both the disc and fovea course directly to the nasal aspect of the disc. Fibers from retinal ganglion cells located between the disc and fovea make up a small portion of the superior and inferior arcuate bundles, along with a larger number of fibers from peripheral temporal retinal ganglion cells. Finally, fibers from nasal macular retinal ganglion cells course directly to the temporal disc. Thus, when there is atrophy of nasal fibers, the normal striations of the nerve fiber layer are lost both nasal to the disc and in the papillomacular region. In addition, nerve fiber bundle slits or defects can be observed in the superior and inferior arcuate bundles. The optic disc shows corresponding atrophy at its nasal and temporal regions with relative sparing of the superior and inferior portions, where the majority of spared temporal fibers (subserving nasal field) enter. Thus, the optic atrophy occupies a more or less horizontal band across the disc, wider nasally than temporally.