Reproducibility of horizontal extraocular muscle insertion distance in anterior segment optical coherence tomography and the effect of head position

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To investigate the reproducibility of horizontal extraocular muscle insertion distance measurements in anterior segment optical coherence tomography (AS-OCT) and to evaluate the effect of eye position on the measurement. The right eyes of 30 healthy young subjects underwent AS-OCT. Varying eye positions were used and the muscle insertion distance was measured by two independent examiners who each measured the insertion distance twice. The measurement was performed for the lateral rectus and medial rectus muscles with the eye rotated 40°, 50°, and 60° to the midline of the instrument. Reproducibility was evaluated with the intraclass correlation coefficient (ICC) and Bland-Altman plot. The lateral rectus insertion distance was smallest with 50° rotation and the medial rectus insertion distance did not show a consistent pattern in regards to gaze position. The differences in insertion distance between different eye positions were not statistically significant for both muscles. The inter- and intraexaminer ICC reproducibility values were excellent for both lateral and medial rectus insertion distance measurements. Inter- and intraexaminer reproducibility were excellent for lateral and medial rectus muscle insertion distance measurements using AS-OCT. The measurements tended to be smallest with the 50° position in lateral rectus measurement; however, medial rectus measurements were variable.