Cardinal features of superior oblique myokymia: An infrared oculography study

PURPOSE: Superior oblique myokymia (SOM) is a rare eye movement disorder characterized by unilateral oscillopsia and binocular diplopia. Our study aimed to better understand SOM using infrared oculography. METHODS: We examined and recorded five patients with SOM. RESULTS: Binocular infrared oculography showed that in primary gaze, all patients exhibited torsional oscillations, which worsened in infraduction and abduction and improved in supraduction and adduction. Saccades showed increased downward saccade amplitudes but normal peak velocities. During fixation in primary gaze, removal of target led to extorsion and supraduction, unmasking underlying superior oblique weakness. CONCLUSIONS AND IMPORTANCE: Our data suggest both weakness and activity-dependent hyperactivity of the trochlear motor unit, supporting a model of injury followed by aberrant regeneration.