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

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.

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.

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).

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.