Lower blepharoplasty using bony anatomical landmarks to identify and avoid injury to the inferior oblique muscle

In the resection of redundant orbital fat during lower blepharoplasty, selective excision is performed from the medial, central, and lateral compartments. During transcutaneous blepharoplasty, the inferior oblique muscle is susceptible to injury because of its intimate association between the medial and central compartments. When performing a transconjunctival approach, the inferior oblique muscle is even more susceptible to injury because it lies in the direct path of dissection for fat pad exposure. Injury to the inferior oblique muscle can result in symptoms ranging from transient diplopia to a more debilitating permanent strabismus. Fresh cadaver heads were used to identify bony anatomical landmarks that would help to more accurately define the origin and body of the inferior oblique muscle. The orbital rim, infraorbital foramen, and supraorbital notch were chosen as guideline landmarks. The origin of the inferior oblique muscle was designated with respect to the above structures, and the muscle course was delineated. The inferior oblique muscle originates on the orbital floor, 5.14 +/- 1.21 mm posterior to the inferior orbital rim, on a line extending from the infraorbital foramen to 10 +/- 0.9 mm inferior to the supraorbital notch along the supramedial orbital rim. The muscle belly extends from this origin to its insertion into the posterolateral globe in an oblique direction toward the lateral canthal area. Identification of the orbital rim, infraorbital foramen, and supraorbital notch more accurately localizes the origin and course of the inferior oblique muscle, which may facilitate fat resection during lower blepharoplasty by preventing morbidity associated with inferior oblique muscle injury.