Comparative study of 3 exophthalmometers and computed tomographic biometry

Purpose: Accurate and reproducible exophthalmometry is mandatory to diagnose and follow-up orbital patients, especially in Graves disease. However, many variations are described among the different commercially available exophthalmometers. Methods: Sixty patients, who underwent a cerebral computed tomography (CT) scan, were included. External prebicanthal segments (EPBCS) for right and left eyes (RE and LE), interorbital distance, and globe axial length were recorded by a first observer (O1), more experienced than a second (O2). Intraobserver and interobserver reproducibility were evaluated, using intraclass correlation coefficient (ICC) and Bland and Altman plots. Results: Concordance between each EPBCS measurement for each eye and CT scan biometry was moderate for the Luedde ruler for the 2 observers. For the Hertel exophthalmometer, concordance was moderate for O1 in the 2 eyes and moderate in RE but good in LE for O2. For the Mourits exophthalmometer, this concordance was very good in RE and good in LE for O1, and good whatever the eye for O2. Intraobserver (ICC varying from 0.75 to 0.95 for the 2 observers) and interobserver (ICC from 0.69 to 0.94) reproducibility were high, especially for the Mourits exophthalmometer. Bland and Altman plots showed underestimations when using the Luedde ruler, overestimations when using the Hertel exophthalmometer, and overestimation of small values and underestimation of high values when using the Mourits exophthalmometer when compared to CT scan biometry. Conclusions: We demonstrated great accuracy to CT scan biometry with 1-prism Mourits exophthalmometer, low accuracy with the Luedde instrument, and intermediate accuracy with the Hertel exophthalmometer, with fair intraobserver and interobserver reproducibility.