Do macular nasal fibers travel more anteriorly or posteriorly in the chiasm?

• A. Anteriorly
• B. Posteriorly
• C. Medially
• D. Laterally

Answer: (B)

In the optic chiasm, the fibers are organized to preserve retinotopic mapping, with central retina (macular) fibers occupying the deepest, most posterior position as they cross to the opposite side. The macular nasal fibers are part of the papillomacular bundle and, when they decussate, run toward the posterior aspect of the chiasm before continuing in the contralateral optic tract. This posterior location explains why central vision is relatively spared in early chiasmal compression and why the answer is posteriorly. The anterior, medial, or lateral placements don’t match the established topography of how macular fibers course through the chiasm.