Comparison of exophthalmos measurements: Hertel exophthalmometer versus orbital parameters in 2-dimensional computed tomography.

OBJECTIVE

To compare the reliability of orbital parameters calculated using 2-dimensional computed tomography (CT) and Hertel exophthalmometry when measuring exophthalmos in normal subjects and in patients with thyroid-associated orbitopathy (TAO).

DESIGN

Retrospective, observational case series.

PARTICIPANTS

CT images of 33 normal orbits and 69 orbits with TAO were included.

METHODS

In central axial CT scans, globe area (GA), orbital area (OA), and GA/OA ratio were calculated by 2 observers using ImageJ. Interobserver agreement was analyzed for Hertel exophthalmometer and CT parameters. In patients with TAO, the association with activity and severity of TAO were also evaluated.

RESULTS

GA and the GA/OA ratio measurements showed excellent interobserver agreement, whereas OA and the Hertel exophthalmometry measurements showed moderate agreement between the 2 observers. GA and the GA/OA ratio were significantly correlated with Hertel exophthalmometry measurements (r = -0.740, r = -0.706, respectively; all p < 0.001). GA and the GA/OA ratio were significantly correlated with the activity and severity of TAO (all p < 0.01).

CONCLUSIONS

GA and the GA/OA ratio were reliable CT parameters with a high intraclass correlation coefficient compared with Hertel exophthalmometer.