A patient with a left homonymous hemianopia is tested with a bright light held in each half of the visual field separately. Shining light on the blind left half produces no pupillary constriction in either eye, while shining light on the seeing right half constricts both pupils briskly. This finding (Wernicke's hemianopic pupil) localises the lesion:
- A Anterior to the lateral geniculate body, in the optic tract
- B At the optic chiasm
- C Posterior to the lateral geniculate body, in the optic radiations or occipital cortex ✓
- D In the Edinger-Westphal nuclei bilaterally
Correct answer: C. Posterior to the lateral geniculate body, in the optic radiations or occipital cortex
Explanation
Pupillary afferent fibres leave the visual pathway at the level of the lateral geniculate body to reach the pretectal nuclei. If a hemianopia is accompanied by a hemianopic pupillary response, the afferent limb is intact and the lesion must lie POSTERIOR to the geniculate body, in the optic radiations or visual cortex. A tract lesion anterior to the geniculate body interrupts these afferent fibres, so the pupil will not react to light in the blind field, killing option A.
Reference: Parsons' Diseases of the Eye, 22nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.