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SYMPTOMS
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Horizontal diplopia, Vertical diplopia in the presence of a skew deviation, Difficulty tracking moving objects, Dizziness on lateral gaze, Headaches, Vertigo
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SIGNS
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Adduction deficit (partial or complete) with a contralateral abduction nystagmus, Type ortho in primary position, Adduction lag in the eye with the adduction deficit, Skew deviation (Higher eye on the side of the lesion), Vertical gaze nystagmus on upgaze
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Convergence is typically intact
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WORK-UP
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Pupils | EOMs | Cover test | Complete eye exam with dilation | Cranial nerve testing | Ptosis testing | OKN drum
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TREATMENT
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Fresnel prisms or patching one eye can help with diplopia
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There is no treatment for INO as it tends to self-resolve (May take days to months with the average being 2-3 months)
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Refer to neuro-ophthalmology/neurology for further evaluation and treatment
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FOLLOW-UP
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Patient will likely be followed up by neurology/neuro-ophthalmology on a regular basis. Patient should be evaluated once underlying neurological etiology is under control or stable
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ADDITIONAL LAB | TESTS
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MRI of the brain with and without contrast (Concentration on the brainstem)
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ETIOLOGY
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Brainstem lesion that involves the medial longitudinal fasciculus (MLF) which leads to a deficit in the ability to control conjugate eye movements. The two most likely etiologies are multiple sclerosis (in younger patients) and a stroke (in older patients)
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DIFFERENTIAL DX
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Chiari malformation, Cranial nerve VI palsy, Cranial nerve III palsy, Progressive supranuclear palsy
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NOTES
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The side of the INO is named after the eye that has the adduction deficit
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An INO secondary to multiple sclerosis tends to be bilateral and an INO secondary to a stroke tends to be unilateral
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Wall-eyed bilateral internuclear ophthalmoplegia (WEBINO) : A bilateral form of an INO that presents with bilateral exotropia in the primary position
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One and a half syndrome: A bilateral form of an INO where there is a deficit of all horizontal eye movements except for abduction in the contralateral eye.
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Eight and a half syndrome: One and a half syndrome with a cranial nerve VII palsy
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