Lesion to Meyer's loop in the temporal lobe causes which quadrantanopia, and on which side?

• A. Contralateral inferior quadrantanopia (pie in the floor); left Meyer's loop lesion yields right inferior quadrantanopia.
• B. Bitemporal hemianopia due to chiasm involvement.
• C. Homonymous hemianopia.
• D. Contralateral superior quadrantanopia (pie in the sky); left Meyer's loop lesion yields right superior quadrantanopia.

Answer: (D)

Meyer's loop is part of the optic radiations in the temporal lobe and carries fibers from the inferior retina, which correspond to the superior part of the visual field. When this loop is damaged, the loss falls in the contralateral upper quadrant of vision, described as a contralateral superior quadrantanopia (pie in the sky). So, a lesion on the left Meyer's loop produces a right superior quadrantanopia. The other patterns don’t fit because chiasm involvement gives bitemporal loss, a post-chiasmal lesion often causes a full homonymous hemianopia, and involvement of the dorsal optic radiation in the parietal lobe would produce a contralateral inferior quadrantanopia.