Horizontal Extraocular Muscle Insertion Site in Relation to Axial Length Using Swept-Source Anterior Segment OCT

PURPOSE: The purpose of this study was to correlate between the axial length of the globe and the insertion site of horizontal extraocular muscles using swept-source anterior segment optical coherence tomography (SS-ASOCT), with posing an equation to calculate the muscle insertion site from the axial length. METHODS: The study design was observational and cross-sectional. It was performed on 157 eyes of 157 healthy subjects. The distance of the medial rectus (MR) and the lateral rectus (LR) insertion sites from the limbus were measured using SS-ASOCT. The insertion sites’ distances were correlated to the axial length (hypermetropes < 22.5 mm, myopes > 24.5). Correlation between numerical variables was done by Pearson’s correlation coefficient and confirmed by linear regression analysis and scatter diagrams. RESULTS: The mean MR insertion site was 5.47 ± 0.19 mm in hypermetropes versus 5.68 ± 0.23 mm in myopes, whereas the mean LR insertion site was 6.81± 0.23 mm in hyperopes versus 7.08 ± 0.16 mm in myopes. The axial length showed a moderate positive, but significant, correlation to the insertional position for the medial and lateral rectus muscles (MR: r=0.417, p<0.001; LR: r=0.410, p<0.001). CONCLUSION: Comparing the horizontal extraocular muscle insertion site to axial length using SS-ASOCT showed a significant positive correlation. The model equation for MR insertion: MR (mm) = 4.522 + 0.045 (AXL in mm) with an R = 0.437, R(2)= 0.191, F=12.071, P<0.001. The model equation for LR insertion: LR (mm) = 5.72 + 0.048 (AXL in mm) with an R = 0.438, R(2)= 0.192, F=12.116, P<0.001.