Lesions of the optic chiasm are most likely to produce which visual field defect?

Lesions of the optic chiasm primarily affect the crossing fibers that carry visual information from the nasal (inner) half of each retina. The fibers from these nasal retinas contribute to peripheral vision in both visual fields. When there is damage at the optic chiasm, these fibers cannot transmit visual signals effectively, leading to a characteristic visual field defect known as bitemporal hemianopia.

In bitemporal hemianopia, the patient loses vision in the outer (temporal) halves of both visual fields, resulting in a ‘tunnel vision’ effect. This visual defect aligns with the anatomy of the optic chiasm, as it is precisely where the nasal fibers cross over to the opposite side.

The other choices do not correspond to the typical effects seen with optic chiasm lesions. Amaurosis fugax refers to temporary vision loss generally caused by vascular issues affecting the eye or retina. Unilateral blindness indicates loss of vision in one eye, which typically suggests a problem along the optic nerve or more distal visual pathways rather than at the chiasm itself. Homonymous hemianopia indicates a loss of vision in the same half of the visual field in both eyes, which is often seen with lesions in the optic tract or visual