After the optic chiasm, do superior fibers travel more medially or laterally?

• A. Medially
• B. Laterally
• C. Anterior
• D. Posterior

Answer: (A)

After the chiasm, the optic radiations keep a retinotopic map of the visual field. The fibers carrying the upper visual field travel through the parietal lobe and lie closer to the midline as they descend through the posterior limb of the internal capsule to the occipital cortex, so they end up more medial. In contrast, fibers for the lower visual field loop forward in Meyer's loop within the temporal lobe and sit more laterally. This medial position of the superior fibers fits with how lesions produce characteristic field losses: parietal pathway lesions → contralateral inferior quadrantanopia, while temporal (Meyer loop) lesions → contralateral superior quadrantanopia. Therefore, superior fibers travel medially.