The correlation between corneal asphericity and higher order aberrations after SMILE surgery

Abstract

Objective To evaluate the characteristics of anterior corneal asphericity and higher order aberrations after SMILE surgery,and to analyze the correlation between them.Methods In this prospective study,41 subjects who underwent SMILE surgery were enrolled with right eyes selected for the study.The asphericity coefficient Q-value at diameters of 6,7,8 and 9 mm and total higher order aberrations (HOA),spherical aberrations (Z40),secondary spherical aberrations (Z60),vertical coma (Z3-1),horizontal coma (Z31),y-trefoil (Z3-3) and x-trefoil (Z33) of the cornea were measured before surgery and 3 months following the surgery.A paired-samples t test and Pearson correlation were used for analysis.Results All Q-values increased from negative to positive after SMILE surgery and the differences were statistically significant (t=-23.558,-26.661,-28.366,-28.788,P＜0.01).Corneal HOA,Z40,Z60,Z3-1 and Z31 increased and the differences were statistically significant as well (t=-11.815,-11.813,-16.209,6.470,4.835,P＜0.01).However,the change in Z3-3 or Z33 was not significant (t=0.278,-1.064,P＞0.05).Among corneal higher order aberrations,a linear correlation was found between the Q-value and corneal HOA,Z40 and Z3-t before surgery (P＜0.05).The change in corneal HOA and Z40 had a positive linear correlation with the Q-value at each diameter (HOA:r=0.554,0.480,0.416,0.352,P＜0.05; Z40:r=0.671,0.577,0.495,0.395,P＜0.05).The difference in Z3-1 had a positive linear correlation with the Q-values at diameters 6 and 7 mm (r=0.377,0.342,P＜0.05).The difference in Z31 had a positive linear correlation with the Q-values at diameters 6,7 and 8 mm (r=0.436,0.385,0.316,P＜0.05).No linear correlation was found between the changes in the Q-values at each diameter and those of Z3 3,Z33 or Z60 (P＞0.05).There was not a linear correlation between the change in the Q-values and lens diameter (P＞0.05).Lens diameter had a negative linear correlation with the changes in HOA and Z40 (r=-0.315,-0.393,P＜0.05).No linear correlation was found between the changes in Z60,Z3-1,Z31,Z3-3,Z33 (P＞0.05).Conclusion The anterior corneal asphericity changed from negative to positive and corneal higher order aberrations increased after surgery.The smaller the lens diameter,the larger the changes in HOA and Z40.There were positive linear correlations between the changes in anterior corneal asphericity and those of corneal HOA,Z40,Z3-1 and Z31 with the change in spherical aberrations having the closest correlation with the Q-value. Key words: Femtosecond laser; Small incision lenticule extraction; Visual quality; Q-value; Higher order aberration