Origin of the Lower Orbicularis Oculi Muscle in Relation to the Nasojugal Groove.

The aim of this study was to clarify the location of the origin of the lower orbicularis oculi muscle (OOM) in relation to the nasojugal groove.In 45 lower eyelids of 44 patients, the origin of the lower OOM was identified. In 4 lower eyelids of 2 fresh cadavers, the breaking strength was measured. In 4 lower eyelids of 4 fixed cadavers, 3 parasagittal sections and 2 horizontal sections were made. In computed tomographic scans of 182 orbits of 99 patients, the maxillary attachment of the OOM was measured.The lower OOM originated along the orbital margin, and the mean (SD) width of the attachment was 10.5 (1.4) mm. The lower OOM ran obliquely laterally and downward. The force needed to tear the 3-mm-wide OOM was 8.40 (0.21) N. Histologically, the OOM was attached to the periosteum on the medial limbus line; however, it was not attached at the midpupillary line or the lateral limbus line. The most medial part of the lower OOM was attached to the periosteum. In the middle and lateral part of the lower eyelid, however, a fibrofatty tissue was found between the OOM and the periosteum. In computed tomographic scans, the OOM was almost always attached to the maxilla at the medial epicanthus (100%) and at the medial limbus line (92.3%). At the midpupillary line, fewer than half (45.6%) were attached. At the lateral limbus line (14.3%) and the lateral canthus (4.4%), they were rarely attached.In a relaxed state, the nasojugal groove is not evident because the attached portion does not pull at the wings. While squinting, the OOM contracts and the vertical width shortens, and thereafter, a surface puckering of the delicate periorbital skin appears.