A 28-year-old man complains of vertical double vision that is worst when reading or walking downstairs. On examination, there is weakness of depression when the affected eye is adducted, and tilting the head toward the opposite shoulder reduces the diplopia. Which muscle is affected?

• A Superior oblique ✓
• B Inferior rectus
• C Superior rectus
• D Inferior oblique

Explanation

The superior oblique intorts the globe and depresses it in the adducted position. Its paralysis produces vertical diplopia that worsens on looking down, such as while walking downstairs, and the classic compensatory head tilt away from the affected side (Bielschowsky head tilt test). Inferior rectus depresses the abducted eye, so depression would be impaired in abduction rather than adduction, which excludes option B.

Reference: Gray's Anatomy for Students, 4th ed.

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