Anatomic Variability of the Human Orbit

Knowledge of the bony orbit and how its volume changes are clinically important in addressing traumatic injuries. Restoration of orbital volume in some patients is critical to achieving successful outcomes after such injuries. In this large cadaveric study, we aimed to assess the average volume, range of bony orbit volumes, degree of volume discrepancy between the right and left orbits, and percentage of skulls with 1- and 1.5-mL orbital volume differences via alginate impressions and volume displacement.

This study used 121 skulls (242 orbits) from the University of Texas Southwestern Department of Cell Biology/Anatomy. Seal-press wrap was first adapted to each bony orbit to ensure no damage to the internal orbits, foramina, or fissures. Alginate impressions were then taken and trimmed to encompass the bony orbit. The volume of each impression was calculated via the volume-displacement method.

The average orbital volume was 26.75 mL for the right side and 26.65 mL for the left. The average right-to-left difference between orbits was 0.8 mL, with a range from 0.02 to 3.64 mL. The calculated methodologic error was 0.91% for the right orbit and 1.05% for the left. Approximately 14% and 21% of skulls showed normal left-to-right orbital volume differences of 1.5 mL or greater and 1.0 mL or greater, respectively.

Our data suggest that the average normal asymmetry between the right and left orbital volumes is 0.8 mL, which is 50 to 80% of the orbital volume increase implicated in traumatic enophthalmos. Of the skulls, 17 (14%) showed a right-to-left orbital volume asymmetry of 1.5 mL or greater and 25 (21%) showed an asymmetry of 1.0 mL or greater. The skull-to-skull orbital volume range approached 200%. Thus, this study provides surgeons with important information to consider when reconstructing a traumatized orbit using a computed tomography scan of the unaffected, contralateral orbit.