Anatomical Variability of the Human Orbit

Introduction Knowledge of the bony orbit and how its volume changes are clinically important in traumatic injuries. Thus, restoration of orbital volume in some patients is critical in achieving successful outcomes following such injuries. In this large cadaveric study, we aim to assess the average volume, range of the bony orbit volume, the degree of volume discrepancy between the right and left orbits, and percent of skulls with 1mL and 1.5 mL orbital volume difference via alginate impression and volume displacement. Materials and Methods One hundred twenty-one skulls (242 orbits) were utilized from the UTSW Cell Biology/Anatomy Department. Seal-press wrap was first adapted to each bony orbit in order to assure no damage to the internal orbits, foramina, or fissures. Alginate impressions were then taken and then trimmed to encompass the bony orbit. The volume of each impression was then calculated via the volume-displacement method. Results The average orbital volume for the right side was 26.75 mL; and for the left side was 26.65mL. The average right-to-left difference between orbits was 0.8 mL, with a range from 0.02 to 3.64 mL. The calculated method of error for the right orbit was 0.91% and the left orbit was 1.05%. Approximately 14% and 21% of the skulls demonstrated normal left to right orbital volume difference of 1.5mL or greater and 1.0mL or greater, respectively. Conclusion Our data suggests that the average normal asymmetry between right and left orbital volumes is 0.8mL, which is 50-80% of the orbital volume increases implicated in traumatic enophthalmos. Seventeen skulls (14%) demonstrated a right-to-left orbital volume asymmetry of ≥1.5mL and 25 (21%) demonstrated an asymmetry of ≥1.0mL. The skull-to-skull orbital volume range approaches 200%. Thus, this study provides surgeons with important information to consider when reconstructing a traumatized orbit using a CT scan of the unaffected, contralateral orbit.