Relative en- and exophthalmometry in zygomatic fractures comparing optical non-contact, non-ionizing 3D imaging to the Hertel instrument and computed tomography

Abstract

Aim: It is the aim of the present study to introduce non-contact, non-invasive optical 3D imaging to relative exophthalmometry and to compare the resulting data to exophthalmometry values assessed by the Hertel instrument and computed tomography. Patients and methods: 20 patients (3 female, 17 male, 44.4±16.6 years) without orbital pathology, who were examined by computed tomography of head and neck for the exclusion of different diseases, and seven patients (1 female, 6 male, 40.1±14.4 years), who received routine orbital computed tomography because of zygomatic fractures, were included in the study. Optical 3D images of the facial surface were assessed and Hertel exophthalmometry was carried out to determine the relative globe position. In patients with zygomatic fractures the assessment of optical 3D images and Hertel values was repeated 5 days after surgery. Results: For patients without orbital pathology relative exophthalmometry data were 1.4±1.1 mm for the Hertel instrument, 0.9±1.0 mm for computed tomography and 0.5±0.5 mm for optical 3D imaging. The values for Hertel exophthalmometry and computed tomography did not differ statistically significantly ( p Hertel difference preop/CT difference preop =0.284), while there was a significant difference between Hertel exophthalmometry and optical 3D imaging ( p Hertel difference preop/optical difference preop =0.008). In the cases of zygomatic fractures, Hertel exophthalmometry revealed less pronounced relative differences in globe position than CT and optical 3D imaging data (Hertel 0.7±1.1 mm, CT 1.9±1.0 mm, optical 3D imaging 1.9±1.0 mm). Postoperatively, relative Hertel exophthalmometry showed an increased value revealing a more pronounced enophthalmos (1.7±1.0 mm), while the corresponding value of the optical 3D images decreased as a sign for normalization of the globe position (1.1±0.7 mm). Conclusion: Because of its reliance on the lateral orbital rims Hertel exophthalmometry can lead to an under- or overestimation of enophthalmos, when soft tissue oedema or a dislocation of the orbital rim are present. The combination of computed tomography as baseline measurement and optical 3D imaging for the follow-up examinations reveal more realistic data in cases of zygomatic fractures. Therefore, they should be preferred to the determination of Hertel values especially in more complex cases.