The Correlation Analysis of Factors Affecting the Effective Optical Zone After SMILE

Objectives: The purpose of this study was to analyze the size of the effective optical zone (EOZ) and its related influencing factors in small incision lenticule extraction. Methods: Calculation of the horizontal EOZ (Y1: H-EOZ), vertical EOZ (Y2: V-EOZ), and average EOZ (Y3: A-EOZ) using corneal topographic difference maps. Multivariate linear regression analysis was used to establish a multivariate linear equation for the dependent variable EOZ. Receiver operating characteristic (ROC) curves were constructed based on the experimental cohort and were validated in the validation cohort. Results: The EOZ was smaller than the programmed optical zone (POZ) (p<0.001), and the spherical (Sp) and astigmatism (As) were positively correlated with H-EOZ (p Sp <0.001, p As <0.001), whereas average K-value (Km) and horizontal corneal diameter (WTW) were negatively correlated with H-EOZ (p Km <0.001, p WTW <0.002). The corresponding multivariate linear regression equation was Y1=5.246+0.168X1−0.278X2+0.027X3−0.131X4. Spherical, As, the asphericity of cornea (Q-value), and POZ were positively correlated with V-EOZ (p As <0.000, p Q <0.001, and p POZ <0.05, respectively) and Y2=3.032+0.102X1+0.175X2+0.642X5+0.415X6. Spherical, astigmatism, and POZ were positively correlated with A-EOZ (p Sp <0.000, p As <0.05, p POZ <0.05, respectively), whereas WTW was negatively correlated with A-EOZ (p WTW <0.004) as follows: Y3=4.384+0.132X1+0.023X3−0.117X4+0.294X6. The H-EOZ model had the largest area under the ROC curve, 0.853 (95% confidence interval: 0.807–0.767). Conclusions: The preoperative intended correction of spherical lesions may be the main factor affecting the size of the postoperative EOZ, and this study has strong predictability for the horizontal EOZ.