Measurement of Anterior Scleral Curvature Using Anterior Segment OCT

Purpose. To investigate and validate methods for measuring the radius of anterior scleral curvature using anterior segment optical coherence tomography images. Methods. Twenty-four volunteers were enrolled in this study. Anterior segment optical coherence tomography images, centered on horizontal/vertical limbus, including adjacent anterior sclera, were obtained in addition to conventional images centered on the optical axis. Central horizontal, nasal, and temporal optical coherence tomography images were consolidated to a new image for subsequent analyses. The reference points of limbal surface and three scleral points were marked nasally and temporally. The radius of a best-fit circle to the six scleral points was derived (the BFC [best-fit circle] method) and the radii of two circles, the centers of which are on the optical axis and pass through the points of the scleral surface at 2 mm from the limbus nasally and temporally, were calculated (the axial method). To assess the reliability and accuracy of each method, intraobserver and interobserver agreements were analyzed and the radii of contact lenses with known curvatures were measured. Results. The mean (+/- SD) radius of a BFC was 13.12 (+/- 0.80) mm. The mean (+/- SD) radius of nasal anterior scleral curvature (13.33 +/- 1.12 mm) was significantly greater than that of temporal anterior scleral curvature (12.32 +/- 0.77 mm) (paired samples t test, p < 0.001). The BFC and axial methods showed excellent intraobserver and interobserver agreements for measurements (intraclass correlation coefficient > 0.75, p < 0.001), whereas both methods showed a tendency to slightly underestimate the actual curvature of a rigid contact lens of known dimensions (-0.07 +/- 0.13 mm [the BFC method] and -0.19 +/- 0.07 mm [the axial method], Wilcoxon signed rank test, p = 0.173 and p = 0.028, respectively). Conclusions. Anterior segment optical coherence tomography is a valuable tool for measuring the radii of anterior scleral curvatures by image processing and mathematical calculation and can provide useful information in specific clinical situations such as designing scleral lenses.