Post-chiasm lesion is most likely to cause which visual defect?

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Lesions after the optic chiasm affect the same visual field in both eyes because the information from each field is carried by fibers that have already crossed or partially reorganized before reaching the chiasm. When a post-chiasm lesion occurs, it interrupts the contralateral visual pathways (optic tract, radiations, or occipital cortex), producing loss of the opposite visual field in both eyes—this is called homonymous hemianopsia. For example, a lesion on the left side after the chiasm will cause a loss of the right visual field in both eyes.

Monocular blindness would require damage to the optic nerve before the chiasm. Bitemporal hemianopsia arises from damage at the chiasm itself, affecting the crossing fibers. Acromatopsia involves color processing deficits, typically from cortical or subcortical areas related to color vision, not a simple field defect from a post-chiasm lesion.