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Y. J. Liao; Superior Oblique Myokymia: Intorsional Nystagmus During Visual Fixation and Extorsion Without Vision. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1809.
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Superior oblique myokymia is an episodic but often severe eye movement disorder characterized by monocular oscillopsia and diplopia due to abnormal activity of the fourth cranial nerve or muscle. The goal of this study is to use eye movement recordings to indirectly assess the mechanism of superior oblique myokymia.
I performed serial binocular 60-Hz infrared oculography (3D-VOG, Sensorimotoric Instruments) on 3 patients with superior oblique myokymia.
My analyses focused on 2 Caucasian women in their 30s-40s with persistent superior oblique myokymia. They both have family history of autoimmune diseases, sulfa allergy, and no history of head trauma. At symptom onset, they experienced episodic shimmering eye movements OS for 2-4 months followed by about 10 symptom-free years and then persistent debilitating symptoms. In primary gaze, both patients exhibited prominent, isolated intorsional nystagmus OS. They had a slight right head tilt and either orthophoria or slight hypertropia OS in primary gaze. In primary gaze, prominent 0.5-2 Hz intortional nystagmus and superimposed high frequency nystagmus (without predominant frequency) were observed. Downgaze exacerbated the intortional nystagmus, with superimposed intortional nystagmus at left and down gaze, a position important during reading. Interestingly, during attempted primary gaze in the dark, both patients demonstrated a gradual disappearance of the intorsional nystagmus and persistent extortion.
Monocular intorsion and intorsional nystagmus observed in 2 patients with persistent superior oblique myokymia were most severe at adduction and infraduction but absent at abduction and supraduction. Paradoxically, the affected eye was extorted in the dark, with gradual disappearance of the nystagmus. This pattern of eye movement abnormality strongly supports a neurogenic pattern of weakness and cannot be attributed simply to spontaneous muscle discharges.
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