A patient has a lesion of the right trochlear nerve (CN IV). Which clinical finding is most specific for CN IV palsy?
- A Vertical diplopia worsened on looking down and to the left, with ipsilateral hypertropia corrected by head tilt to the left ✓
- B Lateral deviation of the right eye at rest with inability to adduct
- C Ptosis, mydriasis, and 'down and out' eye position
- D Diplopia on looking to the right with medial deviation of the right eye at rest
Correct answer: A. Vertical diplopia worsened on looking down and to the left, with ipsilateral hypertropia corrected by head tilt to the left
Explanation
The trochlear nerve (CN IV) innervates the superior oblique muscle, which intorts and depresses the eye (most effective when the eye is adducted). Right CN IV palsy causes the right eye to be relatively elevated (hypertropia) due to unopposed inferior oblique action, and diplopia is worst when looking down and inward (e.g., descending stairs). The Bielschowsky head tilt test: tilting the head to the right worsens right hypertropia; tilting to the left improves it. Options B and D describe abducens palsy. Option C describes CN III palsy with uncal herniation.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.