Magnetic Resonance Imaging of the Medial Rectus Muscle of Patients with Consecutive Exotropia after Medial Rectus Muscle Recession

Abstract

To investigate the morphologic characteristics of the medial rectus muscle in patients with consecutive exotropia. Retrospective, nonrandomized, interventional study. Eleven eyes of 10 patients with consecutive exotropia were studied. Thirteen eyes of 13 age-matched normal subjects were studied as controls. All of the patients underwent an advancement of a previously operated medial rectus muscle. Patients were divided into 3 groups based on the insertion of the medial rectus muscle: Normally recessed stretched scar, and slipped muscle. A comparison was made of the clinical findings, intraoperative findings, and distance from the limbus to the medial rectus muscle measured on magnetic resonance images among the groups. The medial rectus of 4 eyes of 3 patients had normally recessed insertions and 7 eyes had abnormal insertions (3 stretched scars, 4 slipped muscles). The clinical findings were not different among the 3 groups. The magnetic resonance images showed that the medial rectus muscle was located closest to the limbus in the control subjects and most distant in the patients with a slipped muscle (P<0.005). The clinical findings in the patients with a stretched scar and with normally recessed were indistinguishable. Magnetic resonance images of the medial rectus muscles of the control subjects and operated groups are significantly different morphologically. A slipped medial rectus muscle has characteristic magnetic resonance findings that are distinguishable from the muscle with normally recessed and stretched scar.