The effect of different angle kappa on higher-order aberrations after small incision lenticule extraction

Abstract

This study aimed to compare higher-order aberrations (HOAs) after small incision lenticule extraction (SMILE) in patients with different angle kappa. This is a retrospective report in which 341 right eyes of 341 patients who were subjected to SMILE, which used coaxially sighted corneal light reflex (CSCLR) as the treatment zone centered, treated by the same experienced surgeon (LHB) for correction of myopia and myopic astigmatism, preoperative and postoperative spherical equivalent (SE), angle kappa, total higher-order aberrations (total HOA), spherical aberration (SA), vertical coma (VC), horizontal coma (HC), oblique trefoil (OT), and horizontal trefoil (HT), were compared. SMILE showed outstanding performance in terms of safety, efficacy, and predictability. In addition, a comparison of preoperative and postoperative HOAs exhibited the difference of total HOA (P < 0.01), SA (P < 0.01), VC (P < 0.01), and HC (P < 0.01), which was statistically significant; however, for OT and HT with the longer follow-up time, the statistical difference gradually decreased. For stratification of angle kappa into groups based on decantation, angle kappa was divided into three major groups: r < 0.1 mm, 0.1 ≤ r < 0.2 mm, and r ≥ 0.2 mm; the changes of SA (F = 4.127, P = 0.021) and OT (F = 3.687, P = 0.031) exhibited significant difference after 1 year of SMILE. We performed a correlation analysis of all preoperative and postoperative parameters, and the results indicated that the preoperative total HOA was negatively correlated with preoperative cylindrical diopter (DC), and postoperative total HOA, SA, and coma were affected by spherical diopter (DS) and SE. Moreover, we also found a significant difference of SA and VC in the early postoperative with preoperative. SA was positively correlated with Y values and r of 1 year after SMILE. All of the analyzed parameters in the three groups, except for the trefoil, gradually increased over time; however, the trefoil could gradually stabilize over time. We also divided angle kappa into four groups by quadrants; the result showed that the effects of higher-order aberrations were markedly different from the various quadrants. Patients with large angle kappa were able to increase VC and SA postoperatively, and higher HOAs were more significant in patients with high myopia. The differences in quadrants exhibited a diversity of HOAs; this could be attributed to the corneal surface reestablishment and the alteration of angle kappa, but the trend was not apparent. Although all patients displayed increased HOAs after SMILE, the potential application of CSCLR as the treatment zone centered still showed excellent safety, efficacy, and predictability.