Effects of the Gaze Fixation Position on AS-OCT Measurements of the Limbus and Extraocular Muscle Insertion Site Distance

Abstract

Purpose: To investigate the effect of the gaze fixation position on measurement of the limbus and extraocular muscle (EOM) insertion site distance using anterior segment optical coherence tomography (AS-OCT). Methods: Patients undergoing horizontal EOM surgeries were enrolled in this prospective experimental study. The distance between the angle recess and the muscle insertion site was measured using AS-OCT while patients fixed their gaze laterally or medially at inner or outer gaze fixation. The distance between the limbus and muscle insertion was intraoperatively measured using calipers. Results: A total of 46 lateral rectus muscles and 36 medial rectus muscles of 44 patients were evaluated. Significant differences were observed between intra-operative measurements (6.3 ± 0.7 mm) and AS-OCT measurements (5.8 ± 0.7 mm) for the lateral rectus muscle at inner gaze fixation ( P = .0017) and medial rectus muscle at outer gaze fixation ( P = .0003); no difference was observed when the lateral rectus (6.4 ± 0.5 mm) and medial rectus (4.9 ± 0.6 mm) muscles were measured at outer and inner gaze fixation, respectively. Bland-Altman plots showed better consistency at outer gaze fixation than at inner gaze fixation for the lateral rectus muscle; the opposite was observed for the medial rectus muscle. More than 80% of the AS-OCT measurements were within 1 mm of the intraoperative measurements at outer gaze fixation for the lateral rectus muscle and inner gaze fixation for the medial rectus muscle. Conclusions: Gaze fixation at outer gaze fixation for the lateral rectus muscle and inner gaze fixation for the medial rectus muscle was an appropriate technique to assess limbus and EOM insertion using AS-OCT. [ J Pediatr Ophthalmol Strabismus . 2021;58(1):28–33.]

Efforts to improve the surgical outcome for exotropia and investigation of the insertion locations of the extraocular muscles

“…Our analysis found that the distance between the MR insertion location and the limbus, as well as the distance between the LR insertion location and the limbus, did not differ significantly in Taiwanese patients compared with East and Southeast Asian patients (Chinese, Japanese, and Thai, as shown in Supplementary Table of Supporting information S1). 2,3,14 However, we observed that the distance from the MR insertion location to the limbus was significantly longer in Koreans compared with Taiwanese 15 . On the other hand, the distances from the MR and LR insertion locations to the limbus were shorter in Taiwanese patients compared with Indian, Polish, and Turkish patients 4,16,17 .…”

“…4,16,17 Hence, populations from different countries living in geographically close regions may have similar EOM insertion locations. [2][3][4]6,[14][15][16][17][18] As mentioned in the introduction, differences in surgical outcome were believed to be due to differences in surgical conditions and surgeons' technique. However, this study shows that surgical dosages may need to be adjusted not only among different surgeons, but also among different countries.…”

“…Additionally, some studies have reported wider variability in OCT measurements compared with direct (caliper) measurements. 2,[29][30][31][32][33][34] Finally, while some countries have a relatively homogeneous racial composition (e.g., China, Korea, Japan, and Taiwan), others have a more diverse composition (e.g., the United States). Ideally, studies of EOM insertion location and horizontal strabismus prevalence should be compared by race.…”

“…Other subsequent studies in some countries have also shown that EOM insertion location varies. [2][3][4] However, the strength of evidence in retrospective studies is often questioned. To address this gap, we conducted an observational study to investigate the horizontal EOM insertion location in Taiwanese patients.…”

“…Specifically, the distance between the insertion location of the LR and the limbus is significantly shorter in Taiwanese patients than in Caucasian patients, suggesting a possibility of anatomical difference in EOM insertion location between different races. Other subsequent studies in some countries have also shown that EOM insertion location varies 2–4 . However, the strength of evidence in retrospective studies is often questioned.…”