Bitemporal hemianopsia is due to a lesion at which location, and what visual field pattern does it produce?

• A. Loss in the upper half of both visual fields with central vision lost.
• B. Loss in the outer halves (temporal) of both visual fields with central vision preserved.
• C. Complete blindness in one eye.
• D. Bilateral tunnel vision with central vision loss.

Answer: (B)

Bitemporal hemianopsia occurs when the optic chiasm is damaged, affecting the crossing fibers that carry information from the nasal retinas of both eyes. These crossing fibers convey the temporal (lateral) visual fields. When they are disrupted at the chiasm, the outer halves of the visual field are lost in both eyes while central vision remains intact. This pattern is classically seen with lesions that compress the chiasm, such as pituitary tumors, whereas damage behind the chiasm would produce a homonymous hemianopia.