Abstract:AIM:To quantitatively evaluate the vectorial effect of different incision locations on surgically induced astigmatism (SIA) following implantable collamer lens (ICL) implantation and to clarify the relative contributions of the anterior and posterior corneal surfaces to total corneal SIA. METHODS: A prospective study was conducted on 98 patients (162 eyes) who underwent ICL/toric ICL implantation between July 2023 and January 2024. Patients were divided into superior incision group (78 eyes) and temporal incision group (84 eyes) according to the expected postoperative residual astigmatism. Pentacam measurements were performed preoperatively and at 3 months postoperatively to obtain total corneal refractive power and anterior and posterior corneal curvature radii. Anterior and posterior corneal surface powers and total corneal astigmatism were calculated. Thibos vector analysis was applied to decompose corneal astigmatism into orthogonal components J0 and J45, and the changes in J0 (ΔJ0) were calculated for each surface. Multiple linear regression analysis was performed to explore the associations of anterior surface ΔJ0, posterior surface ΔJ0, and incision location with total corneal ΔJ0. RESULTS: This study included 162 patients (162 eyes), with 75 eyes in the superior incision group and 87 eyes in the temporal incision group. A total of 154 patients (154 eyes) completed follow-up: 72 patients (72 eyes) in the superior incision group (17 males and 55 females, aged 25.96 ± 6.17 years) and 82 patients (82 eyes) in the temporal incision group (20 males and 62 females, aged 27.79 ± 6.47 years). In the superior incision group, the total cornea and anterior surface J0 shifted toward positive values (against-the-rule), with ΔJ0 of 0.146 ± 0.108 D and 0.199 ± 0.117 D, respectively, while the posterior surface J0 shifted toward negative values (with-the-rule), with ΔJ0 of ?0.050 ± 0.022 D; the temporal incision group showed the opposite trend. Multiple regression analysis showed an excellent model fit (adjusted R² = 0.943), with anterior surface ΔJ0 as the main influencing factor (B = 0.968, β = 1.137, P < 0.001) and posterior surface ΔJ0 also contributing independently and significantly (B = 1.018, β = 0.297, P < 0.001). Incision location and its interaction terms with anterior and posterior surface ΔJ0 were not statistically significant (all P > 0.05). CONCLUSION: Based on 3 month postoperative follow-up, superior incisions induce a predominant with the rule SIA vector, while temporal incisions induce a predominant against-the-rule SIA vector. Anterior surface ΔJ0 is the primary contributor to total corneal ΔJ0, and posterior surface ΔJ0 also demonstrates a statistically significant association. Incision location exerts no direct independent effect on the magnitude of total corneal ΔJ0; its effect is indirectly realized by inducing specific directional SIA vector changes on the anterior and posterior corneal surfaces.
