Local Deformation of Extraocular Muscles during Eye Movement

Abstract

To study extraocular muscle (EOM) function, the local physiologic contraction and elongation (deformation) along human horizontal EOMs were quantified by using motion-encoded magnetic resonance imaging (MRI). Eleven subjects (healthy right eye) gazed at a target that moved horizontally in a sinusoidal fashion (period, 2 seconds; amplitude, +/-20 degrees), during MRI with an optimized protocol. In addition, EOM longitudinal deformation in two patients with Duane's syndrome type I was analyzed. The horizontal EOMs and the optic nerve were tracked through 15 time frames, and their local deformation was calculated. Eight segments were separated along the EOMs and left-to-right and right-to-left eye movements were compared. In healthy subjects, the maximum EOM deformation was situated at approximately two thirds of the muscle lengths from the scleral insertions. The EOM deformations were similar for the entire movement range as well as in both movement directions. In the two patients with Duane's syndrome type I, the abnormal innervation of lateral rectus muscle affected specific EOM segments only. The posterior muscle segments contracted and the anterior muscle segments relaxed during adduction. Motion-encoded MRI is a useful technique for advancing the understanding of the physiology and pathophysiology of EOMs in humans during eye movement.