A patient with a left optic tract lesion is examined with a fine beam of light directed onto the blind temporal half of the left retina, then onto the seeing halves. No pupillary constriction occurs when light falls on the blind hemiretina. This sign, called the Wernicke hemianopic pupil, helps confirm that the lesion lies:
- A Anterior to the geniculate body, in the optic tract ✓
- B Posterior to the lateral geniculate body, in the optic radiations
- C In the occipital cortex
- D In the Edinger-Westphal nucleus
Correct answer: A. Anterior to the geniculate body, in the optic tract
Explanation
Afferent pupillary fibres leave the visual pathway at the lateral geniculate body to reach the pretectal nuclei. If light shone on the blind hemiretina fails to elicit constriction, the afferent limb itself is damaged, placing the lesion in the optic tract or earlier. Lesions behind the geniculate, such as optic radiation or cortical lesions, spare the pupillary fibres and cannot produce this sign, killing options B and C.
Reference: Parsons' Diseases of the Eye, 23rd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.