Internuclear ophthalmoplegia (INO) is characterised by which clinical finding on horizontal gaze testing?

• A Bilateral conjugate gaze palsy to one side with preserved convergence
• B Skew deviation with vertical diplopia and head tilt
• C Bilateral abduction paralysis with preserved adduction
• D Ipsilateral adduction weakness with contralateral abducting nystagmus; convergence preserved ✓

Explanation

INO results from a lesion in the medial longitudinal fasciculus (MLF) between the ipsilateral PPRF/abducens nucleus and the contralateral oculomotor nucleus. It manifests as: ipsilateral adduction palsy (failure of the medial rectus to adduct on attempted gaze to the contralateral side) with contralateral abducting nystagmus (the abducens nucleus attempts to overcome the failed adduction), while convergence remains intact (which tests adduction via a different pathway). Bilateral INO in young adults is classic for multiple sclerosis.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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