Transnasal Endoscopic Surgical Anatomy of the Orbit and Optic Nerve

The medial orbital compartment, located medially to a sagittal plane passing through the optic nerve, can be accessed nowadays through an endoscopic endonasal approach. The access to the orbital content is performed through fracture and gentle removal of the entire lamina papyracea. Once the periorbit is cut and excised, the extraconal fat tissue is completely exposed. Removal of the extraconal fat allows the exposure of the muscular wall. Further gentle removal of intraconal fat tissue leads to exposure of several neurovascular structures. The transnasal endoscopic corridor allows access not only to the intraorbital compartment but also to the medial part of the superior orbital fissure, the orbital apex region, and the optic nerve. Diversion of the muscular tendons (medial and inferior rectus muscles) at the level of the annulus of Zinn permits identification of the two main branches (superior and inferior) of the oculomotor nerve. Medially to the oculomotor nerve, the optic nerve is visible and below it the ophthalmic artery is appreciable. The optic canal can be then dissected and the optic nerve's dural sheath can be incised starting at the common annular tendon and proceeding in a ventrodorsal direction as close as possible to the roof of the optic canal. This will permit early identification and exposure of the ophthalmic artery preventing any lesions to the artery