A 35-year-old woman with multiple sclerosis develops horizontal diplopia with failure of adduction in the right eye and abducting nystagmus of the left eye. Which gaze position reveals maximal diplopia?
- A Right gaze (looking right)
- B Left gaze (looking left) ✓
- C Upgaze
- D Downgaze
Explanation
This is right internuclear ophthalmoplegia (INO) — a lesion of the right medial longitudinal fasciculus (MLF) between the right PPRF/abducens nucleus and the right oculomotor nucleus. In right INO, the right eye fails to adduct (left gaze), while the left eye shows abducting nystagmus. Diplopia is maximal in left gaze because that is the gaze direction requiring right eye adduction (which is impaired). In young women with bilateral INO, MS is the most common cause; in elderly patients, brainstem stroke is more likely. Convergence is typically preserved in INO, distinguishing it from complete CN III palsy.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.