Introduction

The form of the vertebrate skull is dependent, in part, on the size and shape of the orbit and its contents. The orbit has been an object of interest to surgeons dealing with the growth of the human eye and its surrounding structures (Sarnat, 1981). Experiments have demonstrated that removal of the orbital contents slows orbital growth as well as affecting other regions of the skull (Sarnat and Shanedling, 1970; 1972). The orbit is bounded superiorly by the supraorbital process attached to the frontal bone and inferiorly by the zygomatic arch. It represents a morphological structure that is not planar, extending significantly into all three planes, and requiring that the orbital margin be modeled as a curve in 3-space (Figure 16.1).

Irregular morphological forms such as the orbital margin are particularly difficult to characterize with conventional numerical methods, hence the lack of information on orbital size and shape changes with either growth or treatment.

Elliptical Fourier functions (EFFs) were chosen to numerically describe the shape changes in the growing orbital margin. This is a curve-fitting procedure based on a converging trigonometric series. The specific descriptor utilized was developed by Kuhl and Giardina (1982), as a parametric two-dimensional solution; that is, a pair of equations as functions of a third variable.