Is the Insertional Anatomy of Rectus Extraocular Muscles Binocularly Symmetrical?

Abstract

Purpose: This study was performed to examine the location, width, and insertional shape of rectus extraocular muscles (EOMs), and to elucidate the symmetry of the insertional anatomy of rectus EOMs in the left and right eyes. Methods: EOMs were dissected from their origin to the insertion point in 100 intact orbits of 50 cadavers. The width, location, and shape of 4 rectus EOMs insertions were measured. The insertional shapes were classified into 6 categories: straight, oblique, convex, oblique-convex, concave, and nonspecific types. Results: The most common types of insertional shapes were superior rectus muscle, oblique type (34%); inferior rectus muscle, oblique type (7%); lateral rectus muscle, concave type (41%); and medial rectus muscle, straight type (37%). The distance from the limbus to insertion and the width of rectus EOMs were almost symmetrical between the left and right eyes of the paired specimens. However, the insertional shapes were different in 46% of the superior rectus, 56% of the inferior rectus, 58% of the lateral rectus, and 46% of the medial rectus muscles. In a given individual, 49 individuals demonstrated asymmetric insertional shapes in at least 1 rectus EOM in both eyes. Conclusions: Ocular surgeons should consider the possibility of differences in the insertional shape of rectus EOMs between the left and right eyes, especially when performing rectus EOM recession.