Postchiasmal Inflammatory Lesions

"In contrast to the high incidence of VEP delays that are recorded after optic neuritis, in a group of 13 patients presenting with partial or complete homonymous hemianopia resulting from a postchiasmal inflammatory lesion, only 5 were found to have relatively delayed or attenuated VEPs to stimulation of the affected hemifields (Plant et al., 1992). At follow-up, persistent hemifield VEP abnormalities were seen in only 3 patients. The frequent absence of latency prolongation might suggest a different pathological process in postchiasmal as compared with prechiasmal lesions. An alternative possibility may be that, since optic nerve fibers are concentrated in a smaller volume than the fibers of the optic radiation, demyelinating lesions of similar size may affect a greater proportion of fibers in the optic nerve. Also, the circumstances of optic nerve inflammation (particularly when this occurs within the optic canal) may entail an additional element of compression, leading to more severe demyelination."

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