Width of the orbicularis oculi fibers extending to the upper lip with the lateral and inferior lengths of the orbicularis oculi at the level of the lateral canthus: application to botulinum neurotoxin type A injection for crow's feet.

Objective: The aim of this study was to clarify width of extending fibers of the orbicularis oculi muscle (OOc) to the upper lip and the lateral and inferior lengths of the OOc at the level of the lateral canthus. The obtained data will be helpful to distinguish the muscles underlying the wrinkles around the lateral canthus for a safer and efficient BoNT-A treatment for crow's feet. Methods: The OOcs were investigated in 40 hemifaces from Korean cadavers. This study was approved by the Institutional Review Board of the Catholic Kwandong University (IRB no. CKU-21-01-0603). Results: Some lateral fibers of the OOc (OOc lat) extending to the upper lip were identified at the level of the lateral canthus in 77.5% of the specimens, whereas some inferolateral fibers of the OOc extending to the upper lip were found near the level of the lower margin of the OOc in 22.5%. The mean and maximum widths of the OOc lat extending to the upper lip at the level of the lateral canthus were 6.9 mm±3.3 and 14.3 mm, respectively. Mean lateral length and mean inferior length of the OOc at the level of the lateral canthus were 33.9±4.4 mm and 30.5±3.7 mm, respectively. Conclusion: The present study analyzed the lateral and inferior lengths of the OOc and its extending fibers to the upper lip, thus clinicians can predict the areas and borders of the OOc and its extending fibers to the upper lip underlying the wrinkles around the lateral canthus. [ABSTRACT FROM AUTHOR]