Correct! You are looking at small-amplitude torsional oscillations of the left eye, a condition called superior oblique myokymia. Patients report momentary diplopia or blurred vision, and a twitch in the affected eye. This process is caused by intermittent activation of the superior oblique muscle, either by instability in the contractile properties of the muscle or by inappropriate firing in the fourth nerve. Why this happens is a mystery. Although some observers advocate brain imaging to rule out intracranial causes of fourth nerve dysfunction, the yield is so low that imaging should be reserved for patients who have other evidence of brainstem or peripheral nerve dysfunction. This condition is often misdiagnosed as nystagmus, but the clues are the unique twitching sensation and the fact that the eye movement is strictly monocular! This is not a nystagmus at all but more of a fasciculation—a brief asynchronous contraction of muscle groups. Medications that reduce muscle irritability or nerve conduction sometimes work. Clinicians have reported success with adrenergic beta-blocking agents administered topically or orally. Surgical weakening of the superior oblique muscle has been done for this condition, but the chances of causing persistent diplopia are high, necessitating additional eye muscle surgery that is not always successful.

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