Three-dimensional eye movement analysis of superior oblique myokymia.

PURPOSE: To confirm the idea that sole contraction of the superior oblique muscle causes attacks of superior oblique myokymia (SOM).

DESIGN

Observational case report.

METHODS

A 43-year-old man presented with episodic monocular oscillatory eye movements. Three-dimensional eye movements were recorded using the magnetic search coil system and analyzed as rotation vector. The attacks of SOM consisted of intorsional, depressive, and abductive fast phases and their exponential decaying slow phases.

RESULTS

Average direction of rotation axis for the fast phases while fixating straight ahead was 51.5 +/- 5.4 degrees from depression axis in vertical-torsional plane, 78.7 +/- 4.4 degrees from abduction axis in horizontal-torsional plane, and 76.3 +/- 4.3 degrees from abduction axis in horizontal-vertical plane (+/-SD, n = 50). Time constants of slow phases were less than 0.1 second.

CONCLUSIONS

Quantitative three-dimensional analysis of SOM directly confirmed that the fast phases of SOM attacks were induced by the sole contraction of the superior oblique muscle.