Measurement of the distance between corneal apex and pupil center in patients following small-incision lenticule extraction or implantable collamer lens implantation and its correlation with the surgical-induced astigmatism

To investigate the change in the distance between corneal apex and pupil center after small-incision lenticule extraction (SMILE) or implantable collamer lens (ICL) implantation and its correlation with surgical-induced astigmatism (SIA).

This study included patients who had undergone SMILE (n = 112) or ICL implantation (n = 110) to correct myopia and myopic astigmatism. The angle kappa was measured using a Scheimpflug imaging device (Pentacam) and represented as Cartesian values between the pupil center and the corneal vertex (X, Y) and chord u ( \( \sqrt{{X}^{2}+{Y}^{2}}@ \) orientation), and was compared pre- and post-operative.

Following SMILE, the magnitude of chord u \( (\sqrt{{X}^{2}+{Y}^{2}}\) ) significantly increased in both eyes (Wilcoxon signed-rank test, OD: P<0.001; OS: P=0.007), while no significant change was observed in the orientation. A significant correlation was found between the J₀ component of SIA and the change in the magnitude of chord u for both eyes (OD: R²=0.128, P<0.001; OS: R²=0.033, P=0.004). After ICL implantation, the orientation of the chord u was significantly different in the right eye (Wilcoxon signed-rank test, P = 0.008), and the Y-intercept significantly decreased in both eyes (Wilcoxon signed-rank test, P<0.001). A significant correlation was found between J₀ of SIA and the change in the magnitude of chord u for the right eyes (R²=0.066, P=0.002). A significant correlation was found between J₄₅ of SIA and the change in the magnitude of chord u for the left eyes (R²=0.037, P=0.044).

The magnitude of the chord u increased following the SMILE procedure, whereas the Y-intercept significantly decreased after ICL implantation. SIA was related to the change in the magnitude of chord u.