Transorbital Surgical Corridor: An Anatomic Analysis of Ocular Globe Retraction and the Associated Exposure for the Transpalpebral Orbital Rim Preserving Endoscopic Orbitotomy (TORPEDO) Approach

BACKGROUND AND OBJECTIVES: The transorbital approach varies by the extent of bony removal and the target. Orbital rim-sparing transorbital approach with removal of only the orbit's posterior wall provides optimal cosmetic results, without the need for reconstruction. The size of this corridor, limited by the medial globe retraction, has not yet been defined and is difficult to determine in cadavers because of postmortem tissue desiccation. By using patient-specific models in virtual reality, precise areas and degrees of surgical freedom (AOF and DOF, respectively) provided by globe retraction were calculated. These measurements define a potential maximum safe AOF and DOF, as well as the globe retraction, needed to achieve a sufficient surgical corridor. METHODS: Using a virtual reality system, transorbital rim-preserving craniectomies were performed. The axial and sagittal DOF as well as AOF were calculated lateral to the globe, limited by the orbital rim and globe, with an anterior clinoid target. The DOFs and AOFs were calculated for each degree of medial globe retraction and analyzed using paired t tests. RESULTS: With only 5 mm of retraction, the AOF was 886 mm(2), while at 10 mm, the AOF was 1546 mm(2). This increase between 5 and 10 mm allowed for the largest increase in surgical working corridor (P = .02). At 15 mm of retraction (previously studied point at which intraocular pressure raises), the AOF averaged 2189 mm(2) and axial DOF averaged 23.1 degrees. Eighteen DOF (a previously studied point needed to achieve sufficient working space for 2 instruments) was achieved at 11 mm on average, generating 1675 mm(2) AOF. CONCLUSION: Globe retraction of 11 mm is needed to achieve sufficient DOF for 2 surgical instruments, and 15 mm of retraction is a conservative limit that provides comparable AOFs with similar cranial approaches.