Factors influencing intraocular pressure after femtosecond laser surgery and verification of intraocular pressure correction formulas

AIM: To analyze the factors affecting non-contact intraocular pressure(IOPNCT)measurements after femtosecond laser-assisted small incision lenticule extraction(SMILE), explore the correlation of IOPNCT with central corneal thickness(CCT)and corneal curvature after SMILE, and construct the corresponding regression model which will provide scientific basis for clinical evaluation of the true IOP of patients after SMILE.METHODS: Data from a retrospective analysis of 107 myopic patients(206 eyes)who underwent SMILE and 107 myopic patients(201 eyes)received femtosecond laser-assisted in situ keratomileusis(FS-LASIK)surgery from June 2023 to May 2024 were examined. IOPNCT, CCT, and corneal curvature before surgery and at 1 and 3 mo were collected. The preoperative and postoperative IOPNCT, CCT and corneal curvature were analyzed by ANOVA and Pearson correlation analysis, and multiple linear regression models were constructed to evaluate the association of postoperative changes of IOPNCT, CCT and corneal curvature.RESULTS: There were significant differences in IOPNCT, CCT, and corneal curvature of both SMILE and FS-LASIK patients(all P<0.001), there was no significant difference between two groups and interaction effects(all P>0.05), and the IOPNCT, CCT and corneal curvature at 1 and 3 mo post-surgery were significantly lower than preoperative(all P<0.05). Pearson correlation analysis showed a positive correlation between IOPNCT and CCT at 1 and 3 mo after SMILE(r=0.261, 0.267, all P<0.001), but no significant correlation with corneal curvature(all P>0.05). Multiple linear regression analysis of IOPNCT with CCT and corneal curvature at 1 mo after SMILE indicated that the regression equation was: Y=3.426+0.019X1-0.058X2(Y represents IOPNCT, X1 represents the CCT, and X2 represents the corneal curvature), with statistical significant difference in the equation(F=7.654, P=0.001); the regression equation for 3 mo after surgery was: Y=2.056+0.020X1-0.038 X2(Y represents IOPNCT, X1 represents the CCT, and X2 represents the corneal curvature), with statistically significance in the equation(F=7.903, P<0.001). The regression equation of postoperative IOPNCT change(△IOPNCT)and intraoperative cutting corneal thickness(△CCT)and corneal curvature at 1 mo was Y=-2.252+0.008X1+0.587X2(Y represents △IOPNCT, X1 stands for the △CCT, X2 represents the corneal curvature change value), with statistical significant difference in the equation(F=17.550, P<0.001); the regression equation for 3 mo after surgery was: Y=-2.168+0.024X1+0.281X2(Y represents △IOPNCT, X1 represents △CCT, X2 indicates the corneal curvature change values), with statistical significant difference in the equation(F=16.030, P<0.001).CONCLUSION: After SMILE and FS-LASIK surgery, the IOPNCT value of patients was mainly affected by CCT compared with preoperative surgery, and the short-term use of hormone eye drops, fluorometholone, did not cause a significant increase in IOP; both the IOP correction formula at 1 and 3 mo postoperatively can be used clinically to evaluate and correct actual IOP in patients after SMILE.