Normative measurements of inferior oblique muscle thickness in Japanese by magnetic resonance imaging using a new technique.

Abstract

To measure the thickness of the inferior oblique muscle (IOM) among Japanese by magnetic resonance imaging (MRI) using a new technique. This retrospective observational study included 78 patients (36 males and 42 females) who underwent MRI for detection of a unilateral orbital lesion or examining causes of unilateral retrobulbar pain. The thickness of the IOM was measured on the side without the orbital lesion or symptom. On the quasi-sagittal plane through the optic nerve, the major and minor axes of the cross-section of the IOM were measured. On the coronal plane, the maximum thickness perpendicular to the course of the IOM was measured. All measurements were performed using the digital caliper tool of the viewing software. The major and minor axes on the quasi-sagittal plane and the maximum IOM thickness on the coronal plane were 8.00 ± 1.83mm, 2.98 ± 0.55mm, 3.04 ± 0.55mm respectively. There were no significant differences in IOM thickness measurements between sexes and sides (P > 0.050, Student's t-test). No significant correlation with the major axis (r = 0.064, P = 0.576), minor axis (r = -0.065, P = 0.573) or the maximum thickness on the coronal plane (r = -0.099, P = 0.387) was found in relation to age (Pearson's correlation coefficient). The normative IOM thickness in Japanese was presented on MRI, which were similar among all ages irrespective of sex and side. The new technique we used is easily applicable, and the results may serve as a guide to detect IOM involvement in inflammatory and neoplastic conditions of the orbit.