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Orbital Depth in the Pediatric Patient
Johnny T. Chang, MD, Clinton S. Morrison, MD, Jack Styczynski, BS, William Mehan, MD, Stephen R. Sullivan, MD, Helena O. Taylor, MD.
Brown University, Providence, RI, USA.

PURPOSE
Fractures of the orbital floor and medial wall may result in acute entrapment and long-term enophthalmos. Reconstruction typically involves placement of implants into the orbit in order to reconstruct the floor or wall. This requires familiarity with orbital anatomy, most importantly the location of the optic nerve. An implant placed too deeply in the orbit may impinge on and damage the optic nerve, causing visual disturbances and potentially blindness.
Numerous adult radiographic and cadaveric skull studies have previously been published demonstrating mean orbital depths ranging from 40 to 50 mm. However, here is a lack of such data in the pediatric population. The purpose of this study was to perform quantitative measurements of orbital depth in pediatric patients, and to correlate this depth to age and external head measurements in order to provide a means of estimating orbital depth preoperatively.
METHODS
Consecutive pediatric patients up to the age of 18 who underwent MRI imaging of the head were reviewed. Patients with craniofacial diagnoses or inadequate image quality were excluded. MPRAGE sequences were used due to their improved ability to resolve orbital anatomy. Raw data was then imported into a 3D DICOM data viewer for oblique slice reconstruction and measurements. Orbital depth was measured from the inferomedial aspect of the optic canal to the most anterior projection of the inferior orbital rim. Head dimensions were quantified using the biparietal distance (BPD) and nasion-occipital distance (NOD). Orbital depth was then correlated with age and the sum BPD + NOD. In addition, measurements for 20 randomly selected patients were repeated by an independent observer in order to determine interobserver reliability.
RESULTS
A total of 71 patients were included in the study, ranging from 4 months to 17.8 years of age. There was a strong nonlinear exponential correlation between orbital depth and age, with a correlation coefficient of 0.88 (p < 0.0001). Depth increased rapidly in younger subjects, then leveled off toward a horizontal asymptote of 44.93 mm. There was also a strong linear correlation between orbital depth and the sum BPD + NOD, with a correlation coefficient of 0.83 (p < 0.0001). Interobserver reliability with 2 independent observers was strong with a kappa statistic of 0.79 (0.0001).
CONCLUSIONS
Knowledge of orbital anatomy is critical to safe orbital reconstruction. Despite the fact that orbital fractures are the most common type of facial fractures in children, there is a dearth of data regarding pediatric orbital depth. This study provides a quantitative description of orbital depth in the pediatric population relative to age and to easily obtainable head measurements. Knowledge of these results can improve surgical safety and accuracy in pediatric orbital reconstruction.


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