Study On Changes And Influencing Factors Of Functional Optical Zone After Small Incision Lenticule Extraction For Correcting Myopia

Objective:To explore the size of functional optical zone（FOZ）and the relationship between the FOZ and the change in corneal epithelial thickness and corneal shape after small incision lenticule extraction（SMILE）.Methods:In this prospective clinical study.A total of 69 myopic patients（135 eyes）who underwent SMILE in Shengjing Hospital of China Medical University were selected consecutively from June 2021 to December 2021.According to the predicted spherical equivalent（SE）,treated eyes were divided into two groups:a high myopic group（>-6.00D,69 eyes）and a mild to moderate myopic group（≤-6.00 D,66 eyes）.FOZ and corneal epithelial thickness were measured using a Scheimpflug camera and AS-OCT preoperatively and 3 months postoperatively.Statistical analyses were performed by t test,Pearson correlation,multiple linear regression.Results:All of the optical zones were programmed 6.5 mm.The average FOZ of the patients in the high myopia group and the moderate and low myopia group were 5.10±0.17mm and 5.26±0.24 mm at 3 months after operation.The FOZ of the two groups were reduced,and the reduction in the high myopia group was more obvious.The difference between two groups was statistically significant（t=-4.44,P<0.001）.The corneal epithelial thickness in the 0～2mm,>2～5mm,>5～7mm areas of the two groups increased and the corneal epithelial thickness in the>7～9mm area was slightly decreased compared with preoperative ones.The change of corneal epithelial thickness in the 0～2mm and>2～5mm area of the high myopia group were larger than that of the moderate and low myopia group,and the difference between two groups was statistically significant（t=2.43,P=0.016;t=2.71,P=0.008）.There was no significant difference in corneal curvature and corneal Q value between two groups before surgery（t=0.79,P=0.430;t=0.13,P=0.894）.Three months after surgery,the corneal curvature of two groups was significantly decreased and the corneal Q value was significantly higher than that before surgery.The changes in the high myopia group were greater than those in the moderate and low myopia group,and the difference between two groups was statistically significant（t=-6.26,t=10.86;both P<0.001）.Three months after the operation,the size of the FOZ was positively correlated with the expected SE by surgery（r=0.51,P<0.001）,and was negatively correlated with the change of corneal curvature and corneal Q value（r=-0.48,r=-0.39;both P<0.001）,and negative correlated with the change of corneal epithelial thickness(r_0²mm=-0.37,r_>2⁵mm=-0.32;both P<0.001).Three months after surgery,there were statistically significant differences in total high-order aberration,spherical aberration and vertical Coma between the two groups（t=6.46,t=5.04,t=-4.91;both P<0.001）,and FOZ was significantly negatively correlated withΔHOA,ΔSA,ΔV-Coma（r=-0.59,r=-0.59,r=-0.59;both P<0.001）.Conclusions:The FOZ after SMILE was lower than that expected before operation,the larger the preoperative SE,the more obvious postoperative corneal epithelial remodeling,and the smaller the postoperative FOZ,the more the increase of corneal high-order aberration.Corneal epithelial remodeling and changes in corneal aspheric morphology and curvature can affect the size of postoperative FOZ after SMILE.