Orbital Defect Size Reflects Structural Displacement but Not Ocular Motor Dysfunction: A Cohort Study of 1084 Patients.

Background/Objectives: Orbital defect size is widely used as a surrogate for fracture severity, yet a larger bony opening and direct injury to the extraocular apparatus are not the same. We tested whether defect magnitude provides comparable information about structural displacement and ocular motor dysfunction. Methods: Retrospective cohort of CT-confirmed orbital fractures at a level 1 trauma center, 2001-2023. Repeated records were adjudicated to one index injury per patient, yielding 1084 patients. The estimated two-dimensional defect area (hereafter, defect area) was calculated from maximum sagittal and coronal dimensions and modeled per 50 mm2 using logistic regression, restricted cubic splines, covariate-standardized probabilities, and bootstrap area under the curve (AUC). Results: Median defect area was 143.9 mm2 (IQR 82.6-228.0). Per 50 mm2, adjusted odds increased for content herniation (odds ratio 1.37, 95% CI 1.28-1.48) and documented enophthalmos (1.45, 1.33-1.59) but not for extraocular movement abnormality (1.00, 0.92-1.09) or preoperative diplopia (1.01, 0.92-1.10). From 50 to 300 mm2, standardized probabilities rose by 35.9 and 26.3 percentage points for the structural phenotypes versus 0.2 and 0.6 for the functional phenotypes. Area-only AUCs were 0.670, 0.704, 0.500, and 0.508. Conclusions: Defect magnitude reflects structural displacement but shows little to no association with ocular motor dysfunction in this cohort.