• 11 SECTIONDisorders Saccadic
Superior Oblique Myokymia
Key Facts
•Repetitive monocular downward intorsional saccades and a sensation of twitching or trembling of the affected eye, blurred or double vision, or oscillopsia
•Caused by involuntary contractions of ipsilateral superior oblique muscle
•Episodes occur in flurries in otherwise healthy adults
•Attributed to abnormal excitability of trochlear nerve or instability of trochlear muscle membrane
Clinical Findings
•Small repetitive intorsional movements of symptomatic eye
•All other aspects of ophthalmic and neurologic examinations are normal
Ancillary Testing
• Not necessary if findings are classic
Differential Diagnosis
• If strictly monocular, no other condition need be considered
•If binocular, consider acquired binocular pendular nystagmus (see Acquired binocular pendular nystagmus)
Treatment
•Gabapentin, carbamazepine, baclofen, or propranolol may be effective, but spontaneous remissions are so frequent that medication efficacy not rigorously proven
•Recession of anterior portion of superior oblique muscle may be successful in rare medically refractory cases with disabling symptoms
Prognosis
• Often remits spontaneously for long periods or permanently
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Fig. 11.1 Superior oblique myokymia. The affected eye (right eye here) displays fine rotary oscillations that differ from nystagmus in being initiated by saccades and being arrhythmic. The oscillations are episodic and always monocular!
Myokymia Oblique Superior
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• 11 SECTIONDisorders Saccadic
Square Wave Jerks
Key Facts
•Horizontal back and forth saccades that interrupt fixation
•May be normal variant if small (<5º) and infrequent (<10/min) but otherwise a non-specific sign of brainstem dysfunction
•Produces no symptoms
•Common causes:
•progressive supranuclear palsy
•cerebellar degeneration
•brainstem trauma
•multiple sclerosis
•schizophrenia
•Parkinson disease
•Huntington disease
Clinical Findings
•Horizontal back and forth saccades that interrupt fixation
•Pathologic if amplitude >5º or frequency >10/min
•Often accompanied by:
• saccadic pursuit • hypometric saccades • other neurologic abnormalities
Ancillary Testing
• Choice of tests depends on clinical findings
Differential Diagnosis
•Congenital nystagmus
•Ocular dysmetria
•Ocular flutter
•Voluntary “nystagmus”
•Poor attention
Treatment
• Directed at underlying condition
Prognosis
• Depends on underlying condition
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Fig. 11.2 Square wave jerks. Low-amplitude saccades interrupt fixation and take the eyes off target to one side, where they are briefly still and then return with another saccade to the fixation point. Often mistaken for nystagmus, this eye movement abnormality is actually a saccadic intrusion on fixation. It is a nonspecific sign of brainstem dysfunction.
Jerks Wave Square
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