Transnasal Approach to the Medial Intraconal Space: Anatomic Study and Clinical Considerations

Background: The aim of this study was to illustrate the anatomy of the medial compartment of the orbit by comparing the endoscopic transnasal perspective with the external ones. Methods: 8 orbits from 5 double-injected heads were carefully dissected. An endoscopic anterior transconjunctival dissection was performed in one orbit while an endoscopic transnasal intraconal dissection was conducted in 3 orbits. External dissections (from medial, superior and anterior perspective) were also performed. Results: The role of the medial rectus muscle is emphasised. It represents the first important landmark encountered, covering all the other structures during transnasal approaches. By displacing it, the medial intraconal space with its contents becomes visible: the ophthalmic artery and related branches, the superior ophthalmic vein, the nasociliary nerve and, in the deepest part of the medial compartment, the optic nerve. Conclusion: The medial compartment of the orbit can be addressed transnasally. By displacing the medial rectus muscle, it is possible to gain adequate space for the instruments and to control all of the medial compartment, including the medial aspect of the optic nerve.