Quantitative assessment of osseous, ocular, and periocular changes after hypertelorism surgery

The purpose of this study was to develop a methodology to quantify osseous, ocular, and periocular fat changes caused by correction of orbital hyperte lorism to test the hypothesis that there is a quantitatively predictable re lationship between the movement of the osseous orbit and that of the ocular globe. A retrospective review was performed of 10 patients who were status post unilateral or bilateral transcranial medial orbital translocation, fo r whom there were archival digital data for preoperative and postoperative (mean interval = 30 months) three-dimensional computed tomographic (CT) sca ns. In addition to standard demographic and surgical data, the clinical pre operative and postoperative interpupillary and intermedial canthal distance s were recorded. By using a computer graphics workstation, the CT digital d ata were registered to four surgically unaltered anatomic fiducial points t o allow longitudinal quantitative comparisons. The following three-dimensio nal measurements were made for each patient preoperatively and postoperativ ely: interdacryon and interocular centroid distances, and on a standard ser ies of three horizontal and two vertical planes, the position of the medial and lateral orbital walls, and the thickness of the medial and lateral per iorbital fat (20 orbits). CT digital distances were compared with similar c linical distances when possible. The age at operation ranged from 4.0 to 12 .5 years (mean, 6.6 years). The reduction in interdacryon distance exceeded the reduction in intercentroid distance (mean interdacryon change = -5.3 m m versus mean intercentroid change = -2.7 mm). Although there was a strong correlation between the amount of reduction of the lateral orbital wall and intercentroid distances, there was only a moderate correlation between the reduction in the intercentroid distance and that of the medial orbital wal l. Similarly, there was a moderate correlation between the decrease in thic kness of the lateral periorbital fat and the reduction of intercentroid dis tance but not of the medial orbital fat. In conclusion, medial translocatio n of the orbit does not produce equivalent movement of the ocular globe; ne ither the intermedial canthal nor the interdacryon distance is a useful pre dictor of ocular centroid position; and if the goal of hypertelorism operat ion is reduction of interocular distance, then CT measurement of globe inte rcentroid distance is essential for outcome assessment.