Changes of the effective optical zone after small-incision lenticule extraction and a correlation analysis

The objective of the study is to observe the changes in the effective optical zone (EOZ) after small incision lenticule extraction (SMILE) and explore possible correlations with some influencing factors. In total, 133 eyes after SMILE were divided into the mild to moderate myopia group (- 1.75 D to - 5.75 D, 70 eyes) and the high myopia group (- 6.00 D to - 9.50 D, 63 eyes). The postoperative EOZ was calculated by utilizing the corneal tangential curvature map. Changes in EOZ (△-OZ) were monitored and compared between the two groups. Pearson correlation analysis was conducted to determine the correlation between △-OZ and corneal high-order wavefront aberrations. Multicollinearity analysis and ridge regression analysis were performed to assess the correlation between △-OZ and some corneal parameters. After SMILE, the horizontal EOZ (H-EOZ), vertical EOZ (V-EOZ), and average EOZ (A-EOZ) were significantly smaller than the programmed optical zone (POZ) in both groups (p < 0.05). The difference between V-EOZ and POZ (△V-OZ) and the difference between A-EOZ and POZ (△A-OZ) showed more significant changes in the high myopia group than in the mild to moderate myopia group, and △V-OZ was significantly larger than the difference between H-EOZ and POZ (△H-OZ) in the high myopia group. In both groups, the total high-order aberration (T-HOA) and spherical aberration (SA) both increased after SMILE, and they had a similar significant negative correlation with A-EOZ. Moreover, there was a significant negative correlation between △-OZ and Km (X₁), Q-value (X₂), spherical equivalent (SE, X₃), ablating depth (AD, X₄) and △e (X₆), and a significant positive correlation between △-OZ and △Q (X₅). △H-OZ was expressed as Y₁, △V-OZ as Y₂, and △A-OZ as Y₃. The multiple linear regression equations were as follows: Y₁ = 3.683 - 0.065X₁, Y₂ = 1.549 - 0.469X₂ - 0.059X₃, Y₃ = 4.015 - 0.07X₁ - 0.03X₃, Y₁ = 1.337 - 0.005X₄ + 0.413X₅, Y₂ = 1.265 + 0.469X₅, and Y₃ = 0.852 - 0.002X₄ - 0.398X₆. The correlation degree with △A-OZ was ranked as Km > △Q > Q-value > AD > e-value > △e > SE > △Km, as represented by the ridge regression analysis. The EOZ was irregularly reduced after SMILE, which should be taken into consideration in the design of POZ, especially for high myopia. Consideration of the refractive diopter and corneal topography is advised for the design of POZ, the latter of which has greater reference significance.