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Internuclear ophthalmoplegia (INO)

Occurs when medial longitudinal fasciculus (MLF) on one side is damaged.


  • Older pts – think Brainstem stroke, tumour, infection, inflammation

  • Younger pts – think Multiple sclerosis

  • Wernicke’s encephalopathy

  • Pernicious anaemia

Loss of ADDuction of the SAME eye on the LATERAL gaze to the other side.

Symptoms – diplopia (side gaze) ; oscillopsia ; brainstem disease symp (vertigo, limb weakness).


  • UNILATERAL INO – exotropia (primary position) ; decreased ADDuction on same eye (convergence – adduction improves) ; adducting nystagmus of other eye

  • BILATERAL INO – LARGE exotropia ; decreased ADDuction in both eyes ; WEBINO (wall-eyed binocular INO)

Differentials: Partial CN 3 palsy or myasthenia gravis


  1. MS – resolves itself

  2. Urgent referral to neurologist

  3. MRI brain + contrast

Right INO

Image courtesy of (image used for educational purpose)

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