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)

Image courtesy of (image used for educational purpose) – example of right INO

Differentials: Partial CN 3 palsy or myasthenia gravis


  1. MS – resolves itself
  2. Urgent referral to neurologist
  3. MRI brain + contrast

Location Birmingham Midlands Eye Centre 76 Dudley Road Birmingham B18 7QH UK Phone 0121 554 3801 Hours Mr Ch'ng | Vitreoretinal Clinic Sessions: Monday: 8.30am - 12.30pm Wednesday (alternate): 8.30am - 5.00pm Thursday: 8.30am - 12.30pm Friday: 8.30am - 12.30pm | Vitreoretinal Theatre Sessions: Wednesday (alternate): 8.30am - 5.00pm & Friday (emergency cases): 1.30pm - 5.00pm | Eye Casualty Session: Monday 1.00pm - 4.30pm |
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