What type of vision loss would result from a lesion at the optic chiasm?

A lesion at the optic chiasm typically results in bitemporal hemianopsia, which is characterized by the loss of vision in the outer (temporal) fields of both eyes. This occurs because the optic chiasm is where the optic nerves from both eyes converge and cross over. Specifically, the axons from the nasal (inner) portions of the retinas cross to the opposite side of the brain. When there is damage at the chiasm, it affects these crossed fibers, leading to a loss of peripheral vision in both eyes while the central vision is typically preserved.

In contrast, the other types of vision loss mentioned would not occur from an optic chiasm lesion. Right and left homonymous hemianopsia occur due to lesions further along the visual pathways, usually in the occipital lobe or the optic tract, where visual fields are lost on the same side of both eyes. Central scotoma involves a loss of vision in the central part of the visual field and is commonly associated with retinal diseases or lesions affecting the macula, which are distinct from the effects of damage to the optic chiasm.