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.