Diagnosis:
This is a clinical diagnosis. The underlying cause is determined by investigations
Clinical features:
Diplopia
Classic variant, posterior INO:
- On lateral gaze: Failure of adduction of the contralateral eye, nystagmus of the abducting eye
- Medial rectus is less weak on testing each eye separately
Anterior INO variant:
- Divergent eyes bilaterally, paralysis of both medial recti on testing with both eyes open.
- Medial rectus is less weak on testing each eye separately
Another variant:
- On lateral gaze: failure of abduction of the ispsilateral eye, adduction of the contralateral eye is not impaired.
Lateral rectus is less weak on testing each eye separately
Note: ipsi- & contra- lateral refer to the direction of gaze
Investigations to consider:
MRI: multiple sclerosis, brainstem glioma, brainstem infarct, brainstem hemorrhage, Wernicke encephalopathy
Further Investigations for MS
B1 thiamine levels
Causes of Internuclear ophthalmoplegia (INO):
- Multiple sclerosis
- Brainstem infarct
- Brainstem glioma
- Brainstem hemorrhage
- Wernicke encephalopathy