Computer-assisted orbital volume measurement in the surgical correction of late enophthalmos caused by blowout fractures.

PURPOSE: To evaluate the use of computer-assisted volumetric measurement for the prediction of late enophthalmos and for volume estimation of implant material in the correction of late enophthalmos secondary to orbital blowout fractures (BOF).
METHODS: This is a prospective observational study of 16 patients. Computer-assisted orbital volume measurements were made with the use of axial CT scans. Hertel exophthalmometry was used for the measurement of enophthalmos. The Lancaster test was used for measurement of diplopia. Autogenous bone or hydroxyapatite composite material was used for the repair of orbital defects and the correction of orbital volume expansion in 16 patients with enophthalmos caused by BOF. The volume of implant material was calculated from the orbital volume increment. Patients were followed for an average of 8 months after surgery.
RESULTS: There is a high correlation between the increment of orbital volume and the degree of enophthalmos; 1 cm3 orbital volume increment causes 0.89 mm of enophthalmos. Before surgery, 10 of the 16 patients had moderate enophthalmos (3 to 4 mm) and 6 patients had severe enophthalmos (> or = 5 mm). Six months after surgical intervention, 13 patients (81%) achieved satisfactory results; 3 patients had no enophthalmos and 10 had mild enophthalmos (1 to 2 mm). Three patients had moderate to severe enophthalmos.
CONCLUSIONS: The measurement of orbital volume in patients with BOF can be used to predict the degree of late enophthalmos. Use of the orbital volume increment to determine the amount of implant material can improve the therapeutic outcome in the correction of late enophthalmos caused by BOF.