Impact Of Different Percent Tissue Altered Values On Effective Optical Zone After FS-LASIK

PurposeTo investigate the influence of the degree of corneal tissue alteration on the effective optical zone(EOZ)after femtosecond assisted laser in situ keratomileusis(FSLASIK)and the factors affecting it.MethodThis was a retrospective case-control study.Sixty-eight patients who underwent corneal refractive surgery at the Eye Center of the Second Norman Bethune Hospital of Jilin University from December 2021 to August 2022 and met the screening criteria were selected,with a total of 123 eyes.The eyes were divided into a high PTA group(>40%)and a low PTA group(<40%)with a cut-off value of PTA equal to 40%.A total of 75 eyes were divided into the high PTA group and 48 eyes were divided into the low PTA group.Measurements of uncorrected visual acuity(UCVA),best corrected visual acuity(BCVA),and refraction(spherical and cylindrical)were performed before and 3months after surgery in both groups.Corneal asphericity(Q),total higher-order aberration,and spherical aberration were measured using a Pentacam 3-D anterior segment analyzer,and preoperative and postoperative corneal tangential curvature difference maps were obtained.The curvature difference maps were processed using Image J software,and the EOZ diameter and optical zone centration were calculated.Independent sample t-test was used to compare basic information between groups,and paired sample t-test was used preoperatively and postoperatively.Pearson correlation analysis was used for the analysis of EOZ-related factors and PTA-related factors.Results1.Age,central corneal thickness(CCT),Intraocular pressure(IOP),UCVA,BCVA,and corneal flap thickness were not statistically significant in the preoperative low PTA and high PTA groups(P > 0.05),while spherical,columnar,equivalent spherical,and residual stromal thickness(Residual stromal thickness,RST)were statistically significant(P < 0.05).2.At 3 months after surgery,there was no statistical significance for UCVA,BCVA,spherical lens,column lens,equivalent spherical lens,corneal spherical aberration,and optical zone centration in the high PTA and low PTA groups(P > 0.05),and there was statistical significance for total higher-order aberration,Q-value,and EOZ(P < 0.05).3.Correlation analysis showed that the amount of EOZ change at 3 months postoperatively correlated with preoperative equivalent spherical lens,depth of cut,RST,Q-value,total higher-order aberration,and spherical aberration.4.PTA was correlated with the amount of Q-value variation(P < 0.05)and not with the amount of total higher-order aberration variation,spherical aberration variation,or optical zone centration(P > 0.05).ConclusionAfter patients underwent FS-LASIK,the EOZ decreased in both the high PTA and low PTA groups compared with the preset optical zone,and the effect was greater in the high PTA group.The degree of corneal tissue alteration was positively correlated with the amount of Q-value change.Preoperative equivalent spherical lens degree,depth of cut,RST,Q-value,total higher-order aberration,and spherical aberration can all affect the postoperative EOZ size.