The Pretectal nucleus in the dorsal midbrain mediates the pupillary light reflex via which pathway that explains why cortical blindness (occipital lobe lesion) does NOT abolish the light reflex?

• A Afferent fibers from retinal ganglion cells bypass the lateral geniculate nucleus and synapse directly in the pretectal nucleus ✓
• B Afferent pupillary fibers travel with the optic radiation to the cortex before reaching the midbrain
• C The light reflex depends on the superior colliculus which is independent of occipital cortex
• D Pupillary fibers cross at the optic chiasm but reconnect via commissural fibers in the cortex

Explanation

Afferent pupillary fibers from retinal ganglion cells (specifically melanopsin-containing intrinsically photosensitive RGCs and conventional RGCs) leave the optic tract before the lateral geniculate nucleus and project directly to the olivary pretectal nucleus in the dorsal midbrain. They never synapse in the LGN or visual cortex. Therefore, complete destruction of the occipital cortex causes cortical blindness (no conscious vision) but preserves the pupillary light reflex bilaterally. This anatomical bypass explains why pupillary reflexes can be tested even in comatose/cortically blind patients as a measure of midbrain integrity.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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