Hertel exophthalmometer versus computed tomography scan in proptosis estimation in thyroid-associated orbitopathy

Objective: To compare exophthalmometry measured by Hertel exophthalmometer versus computed tomography (CT) scan. Methods: For this study, 133 patients with thyroid-associated orbitopathy (TAO) were analyzed retrospectively. Two experienced clinical observers independently measured proptosis using a Hertel exophthalmometer. The CT approaches used to measure proptosis included two previous methods and one new method. Method 1 used both lateral orbital rims-corneal surface in the axial plane, method 2 used lateral to medial orbital rims-corneal surface in the axial plane, and method 3 used superior to inferior orbital rims-corneal surface in the sagittal plane (new method). Patients were separated into two groups based on 2-mm differences in proptosis between eyes. Correlation analysis was performed to find the association between Hertel and CT values. Results: The Pearson's coefficient (r) was 0.727 for Hertel exophthalmometry and CT method 1, 0.712 for Hertel and CT method 2, and 0.623 for Hertel and CT method 3. For patients with eye proptosis differences larger than 2 mm between eyes, Pearson's coefficient (r) was 0.495 for Hertel exophthalmometry and CT method 1, 0.634 for Hertel and CT method 2, and 0.635 for Hertel and CT method 3. Conclusion: The three CT methods mentioned above had statistically significant relationships with Hertel exophthalmometry. Methods 2 and 3, which measured both eyes through different cut sections, had a significant relationship with Hertel values with eye proptosis differences larger than 2 mm. Thus, the new additive method may be effective for measuring proptosis in patients with differences greater than 2 mm between eyes.