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Assess ocular versions in pursuit and saccades, looking for slow or deficient adduction
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Look for incomitant exodeviation greatest in contralateral gaze
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Tip:
testing with the optokinetic strip or drum, which elicits repetitive saccades, helps to detect a subtle saccadic adduction deficit
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Tip:
look for nystagmus, saccadic pursuit, skew deviation, and ataxia to support a diagnosis of internuclear ophthalmoplegia
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Trap:
a misdiagnosis of partial third nerve palsy occurs often in this setting
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Tip:
the sparing of adduction in convergence helps exclude a partial third nerve palsy, but it is not a trustworthy sign or easy to interpret
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Tip:
if there is no ptosis, pupillary abnormality, deficit in vertical ductions, or incomitant vertical misalignment, the diagnosis of third nerve palsy is unlikely
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Tip:
internuclear ophthalmoplegia may display normal alignment or exodeviation is primary gaze position; the finding of normal alignment is a vote against the diagnosis of partial third nerve palsy
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Trap:
myasthenia gravis and orbital restrictive syndromes are other important imitators of internuclear ophthalmoplegia (“pseudointernuclear ophthalmoplegia”), so be sure to look for the attributes of those conditions
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Tip:
distinguishing internuclear ophthalmoplegia from partial third nerve palsy is important because internuclear ophthalmoplegia is always caused by an intra-axial (brainstem) lesion whereas partial third nerve palsy is usually caused by an extra-axial lesion; if you diagnose internuclear ophthalmoplegia, order brain MRI; if you diagnose partial third nerve palsy, order CTA to rule out aneurysm
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Trap:
in internuclear ophthalmoplegia, MRI often does not show a correlative lesion
