The Effect Of Different Kappa Angle On Visual Outcome And Corneal High-order Aberrations After Small Incision Lenticule Extraction

Background and Objective:With the continuous development of refractive surgery and the increase of myopia,the number of people choosing corneal refractive surgery to correct myopia is increasing year by year.As one of the most advanced methods of corneal refractive surgery,Small incision lenticule extraction(SMILE)has become a mainstream corneal refractive surgery.It is characterized by "valvular incision" and "minimally invasive".Kappa Angle refers to the Angle between the optic axis(the line between macular fovea and the light source)and the pupil axis(the line between the pupil center and the corneal fixed point).In patients with large Kappa Angle,the distance between the pupil center and the visual axis increases.However,due to the lack of intraoperative active eye tracking or iris positioning and other objective guidance and positioning systems in SMILE surgery temporarily,Whether surgery will increase the probability of eccentricity and thus affect the postoperative visual quality of patients has aroused our thinking.On the premise of central positioning by Tear film mark centration method,this study compares the visual effect and high-order aberration of cornea of patients with different sizes of Kappa Angle after smiling and aberration.To observe and analyze the effect of Kappa Angle on the corneal aberration and the correlation between Kappa Angle and corneal aberration.Methods:Prospective Case-control Study.The study included 113 eyes(113 patients)who underwent SMILE in the Ophthalmic Center of the Second Affiliated Hospital of Guangzhou Medical University from January 2019 to October 2019.Coordinate value of kappa angle which obtained from the Pentacam anterior segment analysis system preoperatively was used for grouping.The bigger absolute values of pupil X or pupil y were set up as R,group A was 0 ≤ R < 0.1(18 eyes),group B was 0.1 ≤ R< 0.2(58 eyes),group C was 0.2 ≤ R < 0.3(24 eyes),group D was R ≥0.3(13 eyes).All patients were treated with routine examination and SMILE.Tear film mark centration method was used to determine the treatment center.All surgeries were finished by same well-experienced surgeon.The patients were examined for uncorrected distance visual acuity(UDVA),best corrected distance visual acuity(BCVA),objective and subjective refraction,Pentacam anterior segment analysis system before operation and 1 month,3 months,13 months after operation.The effective index,safety index,percentage of patients within ± 0.50 D,± 1.0D and the average diopter of 1 day,1month,3months and 13 months after operation were calculated for analysis.The corneal aberrations(root mean square of total high-order aberration,vertical coma,horizontal coma,total coma,vertical trefoil,horizontal trefoil,spherical aberration)were obtained from Pentacam anterior segment analysis system.The aberrations of the four groups was compared with the changes of corneal high-order aberrations before and 13 months after SMILE.SPSS 25.0software was used for statistical analysis.The continuous variables are expressed by mean ± SD,and the normal distribution test is carried out by Kolmogorov-Smirnov test;the classification variables are expressed in frequency distribution and percentage.The data of preoperative and postoperative were compared by paired t-test.Single factor variance analysis was used for comparison between groups.Pearson linear correlation analysis was used to analyze the correlation between kappa angle size and higher order aberrations.P < 0.05 was statistically significant.Results:1.There was no significant difference in age,gender,IOP,CCT,UDVA and SE(P > 0.05).2.The effective index of four groups was 1.31 ± 0.20,1.20 ± 0.20,1.21 ± 0.20,1.23 ±0.20.There was no significant difference among the groups(P = 0.250).The safety index of four groups was 1.31±0.20,1.24±0.19,1.25±0.21,1.25±0.21.There was no significant difference among the groups(P = 0.668).After 13 months of SMILE,The SE of percentage of patients within ±0.5D was 77.8%,63.8%,83.3%and 84.6% respectively.The percentage of patients within±1.0D was 94.4%,93.1%,91.7% and 84.6% respectively.There was no significant difference in the percentage of people within ±0.5 D and ±1.0D among the groups.3.There was no significant difference in the higher-order aberrations(RMS HOA,vertical coma,horizontal coma,total coma,vertical trefoil,horizontal trefoil,total trefoil,spherical aberration)among the four groups before SMILE(P >0.05).After 13 months of SMILE,the RMS HOA,vertical coma,total coma and spherical aberration of all patients were increased compared with those before operation(P < 0.01),but the changes of RMS HOA,vertical coma,total coma and spherical aberration of the four groups(compared with those before operation)were not statistically different(P > 0.05).Conclusion:1.While tear film mark centration method was used to determine the treatment center,the results show that SMILE is effective,safe,predictable and stable for different sizes of kappa angle patients.2.The higher order aberrations of cornea after SMILE were higher than those before operation.However,there was no significant difference in the total higher-order aberrations,coma and spherical aberrations among patients with different kappa angles.There was no correlation between the kappa angle and the higher-order aberrations of cornea,which would not induce greater higher-order aberrations.It is suggested that when the treatment center is accurate,SMILE is safe and effective for patients with different sizes of Kappa angle.Large Kappa angle does not induce additional corneal aberrations.The same good visual results can be obtained after SMILE.