Measurement of globe position in complex orbital fractures. I. A modification of Hertel's exophthalmometer, using the external auditory canal as a reference point.

Where there has been displacement or removal of the lateral orbital rim or zygomaticomaxillary complex secondary to trauma or surgery, the measure of globe position by the Hertel exophthalmometer is problematic and inaccurate. A modification of Hertel's instrument that uses the external auditory canal (EAC) rather than the orbital rim as reference point has been developed. Measurement of globe position of 120 normal volunteers was obtained with the Hertel and the modified EAC-fixated exophthalmometer. Although the mean absolute difference between right and left measurements for both methods (Hertel mean, 0.36 mm; modified mean, 0.51 mm; n = 120) differed statistically from 0 (p = 0.0001), that difference was not clinically significant. A more meaningful comparison was that of the variability of the two methods. The variance of the Hertel method (0.32) did not differ from the variance of the modified method (0.40; p = 0.06). No statistically significant difference was noted for sex (p = 0.33) or for race (p = 0.11). We believe this instrument to be of practical use in the assessment of enophthalmos or exophthalmos in patients whose facial deformity, trauma, surgery, or disease precludes the use of a rim-based exophthalmometry.