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SYMPTOMS
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Horizontal diplopia especially at distance
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SIGNS
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Esotropia in primary gaze, Inability to abduct, Esodeviation is worse when looking in direction of affected eye, Head turn toward the affected eye
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WORK-UP
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Pupils | EOMs | Cover test | Complete eye exam with dilation | Cranial nerve testing | OCT of the optic nerve (Rule out papilledema) | Forced duction testing
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TREATMENT
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If cranial nerve VI palsy is acute onset and due to trauma, the patient should be referred to a neuro-ophthalmologist/neurologist/PCP/ER ASAP
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Children or Adults under the age of 50 years old with an acute onset CN VI palsy should be referred to a pediatric ophthalmologist/pediatrician/neuro-ophthalmologist/neurologist/PCP/ER ASAP
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Adults over the age of 50 years old with an acute onset CN VI palsy can be observed and referred to their PCP for a vascular work-up but strong consideration should be given to referring patient to a neuro-ophthalmologist/neurologist/PCP/ER if there is no improvement within 1 month, if there is progression, if there is aberrant regeneration, if there are other neurological symptoms, if there is a history of cancer, if there is optic nerve edema, or if CN VI palsy is bilateral
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Fresnel prisms can temporarily help with diplopia with acute onset CN VI palsies
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Treatment depends on the underlying etiology of the CN IV palsy
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FOLLOW-UP
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Monitor monthly until complete resolution
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ADDITIONAL LAB | TESTS
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Neuro-imaging is typically ordered through neuro-ophthalmologist/neurologist/PCP/pediatric ophthalmologist/pediatrician/ER and may include the following: MRI of the brain with and without contrast | CT of the brain with and without contrast | MRA | CTA | Lumbar puncture
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If etiology is suspected to be due to vascular ischemia or inflammatory, the following should be ordered through the patient’s PCP: Blood pressure evaluation | Fasting blood sugar | HbA1c | CBC with differential | ESR | C-reactive protein | ANA | Lyme titer | ACE
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ETIOLOGY
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Cranial nerve VI damage (from any point from the pons to the lateral rectus muscle) can be secondary to the following: Vascular ischemia from systemic diseases such as diabetes | Trauma | MS | Meningitis | Increased intracranial pressure Compression from a tumor or aneurysm | Infiltrative | Congenital due to incomplete development of the nucleus or nerve (Uncommon)
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There are many potential etiologies as CN VI has the longest intracranial course of any cranial nerve
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DIFFERENTIAL DX
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Myasthenia gravis, Duane syndrome, Thyroid eye disease, Pseudotumor cerebri, Internuclear ophthalmoplegia, Chronic progressive external ophthalmoplegia
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NOTES
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The most common EOM palsy in adults
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