Clinical Study Of Corneal Asphericity And Visual Quality After Q-factor Guided Femtosecond LASIK

ObjectiveComparing the differences of corneal asphericity and contrast sensitivity under different conditions before and after Q value-guided FS-LASIK and standard FS-LASIK for myopia.The postoperative visual acuity,diopter and corneal aberrations were used to evaluate the efficacy of two surgical methods for treating myopia.MethodsProspective cohort study.A total of 64 moderate and low myopia patients（33 patients（64 eyes）in the Q-guide group and 31 patients（62 eyes）in the standard group）treated by Femto-LASIK have been selected from our hospital laser center in the same period.The visual acuity,Q value,corneal aberration and contrast sensitivity were measured and compared before and after surgery.All the cases were followed up for 1,3months.Repeated measures analysis of variance and t-test were used for data analysis.Results（1）There was no statistical difference among the datas before surgery.The uncorrected isual acuity（UCVA）and residual refractive error of all eyes were no significant ifference between the two groups after 3 months’follow-up.The postoperative ncorrected visual acuity（UCVA）of all eyes was satisfying after 3 months’ ollow-up.There was no one line lost in BCVA at 3 months after surgery compared with preoperative BCVA.None of the two groups lost more than one line of best corrected visual acuity（BCVA）.（2）Changes in corneal Q value:In the 6mm diameter range,the postoperative Q values f both groups were positively shifted（P<0.05）.At 3 months,the Q value of the -value guided group was smaller than the standard group,and the difference was ot statistically significant.（P>0.05）.In the 4.5mm diameter range,the Q value of he standard group had a positive trend toward the positive value（P<0.05）,and the value of the Q-value guided group did not change with time（P>0.05）.The Q alue was lower than the standard group and maintained a negative Q value sphericity（P<0.05）.（3）Changes in corneal SA and coma:In the 6mm diameter range,the postoperative orneal SA and coma of two groups was higher than that before surgery（P<0.05）.At 3 months after operation,there was no significant difference in spherical berration and coma between the two groups（P>0.05）.In the 4.5mm diameter ange,there were obviously change of corneal SA and coma during 3 months’ ollow-up visit（P<0.05）,and the spherical aberration of the two groups decreased fter surgery（P<0.05）.At 3 months after surgery,the spherical aberration in the -value guided group was lower than that in the standard group,and the difference as statistically significant（P<0.05）.（4）Contrast sensitivity:At 1 month postoperation,the contrast sensitivity of two groups had increased comparing preoperation.Especially in the photopic circumstances ith glare,CS in 3c/d and 6c/d space frequency were higher than preoperative evel（P<0.05）.In the two groups after operation,the contrast sensitivity returned to he preoperative level at different spatial frequencies in various environments,and t tended to be stable at 3 months after operation.At 3 months after operation,the ontrast sensitivity in different space frequency and environments were improved ompared with 1 month after operation,but the difference was not statistically ignificant（P>0.05）.At 3 months after surgery,the visual quality of the Q alue-guided group was better than that of the standard group under mesopic ircumstances with glare（Z3c/d=-2.0,Z6c/d=-2.1,P<0.05）.（5）Analysis of factors related to△Q:The change of corneal 6mmQ value between the two groups was negatively correlated with the preoperative spherical equivalent（SE）and corneal curvature.△Q_{S group}=5.242-0.215*SE-0.122* curvature（R²=0.64,F=54.3,P<0.05）;△Q_{Q group}=4.169-0.258*SE-0.102*curvature （R²=0.78,F=110.3,P<0.05）.（6）Comparison Q between groups divide by related factors:In the same ablation mode,the change of Q value in the Curvature>43D group was less than Curvature<=43D group,and the difference was statistically significant(t_{S group}=3.69,t_{Q group}=2.62 P<0.05);In the Q<=-0.26 group,the 4.5mm△Q of Q customized ablation group was less than the standard group and the difference was statistically significant（t=3.340,P<0.01）.ConclusionsQ value-guided LASIK for myopia and astigmatism is safe and effective as well as standard FS LASIK.Furthermore,the Q-value guided FS-LASIK could reduce the SA and maintain negative Q value in the range of 4.5 mm.Q value-guided LASIK has better visual quality than standard FS LASIK under mesopic circumstances with glare.In addition,Selection of suitable patients of the higher cornea curvature and more negative Q value can take advantage of maintaining the corneal asphericity after Q-value guided LASIK.