Influence and significance of angle Kappa on total ocular aberrations before and after SMILE surgery

Objective

To investigate the influence of angle Kappa on total high-order aberration (HOA) before and after small incision lenticule extraction (SMILE).

Methods

An observational case series study was conducted.Right eyes of 98 patients with myopia and myopic astigmatism who underwent SMILE surgery at Tianjin Eye Hospital from April 2015 to May 2016 were selected.Uncorrected visual acuity (UCVA), spherical diopter and cylindrical diopter under cycloplegic condition were examined before the surgery and at l and 3 months postoperatively.The chord distance of angle Kappa was measured by Pentacam topography.Wavefront aberrations were measured by WaveScan aberrometer.Pre- and postoperative UCVA, refractive status and each HOA were analyzed.The relationship between angle Kappa and each HOA was analyzed by Pearson correlation.This study adhered to the Declaration of Helsinki.The study protocol was approved by an Ethics Committee of Tianjin Eye Hospital (No.TJYYLL-2017-17). Written informed consent was obtained from each subject.

Results

The preoperative, postoperative 1-month and postoperative 3-month UCVA (LogMAR) were 0.06±0.23, -0.03±0.07 and -0.05±0.07, respectively, showing a statistically significant difference (F=779.330, P<0.001). There were statistically significant differences in spherical diopter, cylinder diopter and spherical equivalent (SE) between before and after operation (F=1 107.811, 127.786, 1 191.266; all at P<0.001), and the postoperative spherical diopter, cylinder diopter and SE were significantly lower than those before surgery (all at P<0.001). At 6-mm pupil diameter, significant differences were found between postoperative total HOA, spherical aberration, coma, the third-order aberration (S3), fourth-order aberration (S4), fifth-order aberration (S5) and sixth-order aberration (S6) and the preoperative values (F=75.915, 78.231, 66.186, 64.521, 97.161, 36.623, 28.852; all at P<0.001). The postoperative 1- and 3-month total HOA, spherical aberration, coma, S3, S4, S5 and S6 were significantly increased in comparison with those before surgery (all at P<0.05). There was a positive correlation between angle Kappa and total HOA, coma and S3 at 1 and 3 months after surgery (total HOA: r=0.357, 0.363; both at P<0.001.coma: r=0.310, 0.341; both at P<0.01.S3∶r=0.343, 0.371; both at P<0.01). Significant differences were found in preoperative, postoperative 1-month and 3-month total HOA, coma and S3 between groups with different angle Kappa (F_group=3.363, 4.277, 4.029; all at P<0.05). The postoperative total HOA, coma and S3 of the larger angle Kappa group were greater than those of the smaller angle Kappa group, with statistically significant differences between them (all at P<0.05).

Conclusions

A larger angle Kappa may induce HOAs in SMILE surgery.

Myopia/surgery; Corneal surgery, laser; Corneal wavefront aberration; Femtosecond laser; Small incision lenticule extraction; Wavefront aberration; Angle Kappa