A 24-year-old man presents with vertical diplopia that worsens when reading in bed and descending stairs. Cover testing shows left hypertropia that increases on right gaze and on tilting the head to the LEFT shoulder. The affected muscle is:
- A Left inferior rectus
- B Right superior oblique
- C Left superior oblique ✓
- D Right superior rectus
Correct answer: C. Left superior oblique
Explanation
The three-step test identifies the palsied cyclovertical muscle. Left hypertropia implicates depressors of the left eye or elevators of the right. Worsening on right gaze implicates the left superior oblique or right superior rectus. Worsening on head tilt to the same side as the hypertropic eye implicates the intorter of that eye, the left superior oblique. C positive Bielschowsky head tilt test on the side of the hypertropia confirms a superior oblique palsy, the commonest isolated cranial nerve palsy causing vertical diplopia.
Reference: Parsons' Diseases of the Eye, 23rd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.