Walsh & Hoyt: Bilateral Lesions of the Optic Nerves

The visual fields of both eyes may be altered by a single lesion posterior to the optic chiasm, by a single lesion affecting the chiasm itself, or by bilateral optic nerve lesions. In the majority of cases, the distinction between a single chiasmal or retrochiasmal lesion and lesions of both optic nerves is not difficult. Bilateral central, cecocentral, and arcuate defects all suggest dysfunction of both optic nerves. Ring scotomas do the same when there is no visible retinal abnormality to account for them. Bitemporal visual field defects are usually produced by a single lesion affecting the optic chiasm, whereas homonymous visual field defects are invariably produced by a single lesion affecting the visual sensory pathway posterior to the optic chiasm. Bilateral altitudinal field defects usually are caused by bilateral retinal or optic nerve lesions, although, rarely, they may be caused by bilateral postgeniculate lesions as well.