Intra-observer and inter-observer variation of Hertel exophthalmometry

Purpose: This study investigated the intra-observer and inter-observer variation of Hertel exophthalmometry. Methods: Seventy normal Chinese adults had bilateral exophthalmometry performed by two examiners. The two examiners were masked to the measurement results. One examiner did the measurement twice and the other examiner measured it once; the order was randomised. The same Hertel exophthalmometer was used throughout the study. The Bland-Altman method was used to analyse the intra-observer and inter-observer agreement. Results: The mean intra-observer and inter-observer agreements on the interorbital distance (IOD) were ±3.31 mm and ±6.39 mm, respectively. The intra-observer exophthalmometry difference was -0.01 ± 0.61 mm for the right eye and 0.09 ± 0.56 mm for the left eye. Agreements were ±1.19 mm and ±1.09 mm for the right and left eyes, respectively. The inter-observer exophthalmometry difference was -0.61 ± 0.89 mm for the right eye and -0.49 ± 0.80 mm for the left eye. Agreements were ±1.74 mm and ±1.57 mm for the right and left eyes, respectively. There was no significant intra-observer difference but the inter-observer difference was significant on both the IOD and exophthalmometry. Conclusion: Good intra-observer agreement was demonstrated using Hertel exophthalmometry. The inter-observer agreement was clinically acceptable.