Comparison of methodologies in volumetric orbitometry.

Purpose: The rate at which the orbit matures is not well-documented. Limiting this pursuit are the difficulties inherent in measuring orbital volumes accurately. This study compared 3 common methods of determining orbital volume and sought to identify an accurate, practical manner for doing so.

Methods: The volume of 1 orbit of 8 human cadaver heads was independently measured using 3 different methods: 1) CT was performed, and images were analyzed with 3-dimensional (3D) volumetric software; 2) The same orbits were then exenterated and a silicone cast was taken. The cast volumes were measured by water displacement; 3) The orbits were then filled with 1-mm glass beads that were transferred to a graduated cylinder where their volume was determined. The data were analyzed statistically.

Results: Intraobserver agreements were good for both beads and casts. Interobserver agreements were good for both beads and CT (p > 0.05). Values obtained using the bead method were equal to values obtained using the cast method (p > 0.05). However, agreement between direct (orbital fillers and casts) and indirect measurements (radiographic techniques) was not satisfactory (p < 0.05).

Conclusions: Independent of method, determining orbital volume is inherently difficult owing to the hyperbolic parabola that is the orbit entrance; all methods require estimation. Glass beads and casts yielded more reproducible values but can only be used in cadavers. CT measurement is prone to error due to the variability of methodologies used but allows access to enormous testing populations. Interstudy comparison is currently not possible. CT volumetric software with strict universal standards for estimating the anterior limit of the orbit appears to be the best method of studying human orbital volumes.