Pre PACES Podcast #86 Internuclear ophthalmoplegia
Apr 28, 2024
Dr Kim Monks, a neurology registrar with neuro-ophthalmology expertise, explains internuclear ophthalmoplegia and the anatomy behind it. They cover cranial nerves, the medial longitudinal fasciculus, how to spot INO on examination, common causes like MS and stroke, and investigation and management approaches. A light quiz on eyes in culture closes the chat.
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Why The MLF Is Central To Eye Coordination
- The medial longitudinal fasciculus (MLF) links the abducens nucleus on one side to the oculomotor nucleus on the other to preserve conjugate gaze.
- The MLF decussates quickly, is heavily myelinated and lies medial, explaining ipsilateral adduction failure with contralateral abduction nystagmus.
How To Recognize And Localize An INO
- Diagnose internuclear ophthalmoplegia (INO) when the ipsilateral eye fails to adduct and the contralateral abducting eye shows nystagmus during horizontal gaze.
- Label the INO by the side of the adduction failure because the lesion in the MLF is ipsilateral to that eye.
Where You'll Detect An INO In Examination
- Test for INO during the H test of eye movements by asking the patient to follow your finger left and right at eye level.
- Watch for a non-adducting eye with the opposite eye showing horizontal nystagmus on attempted gaze.