Vector analysis of small incision lenticule extraction and toric implantable collamer lens implantation for astigmatism correction

Objectives: To compare the efficacy of small incision lenticule extraction (SMILE) and toric implantable collamer lens (TICL) implantation for myopic astigmatism correction using vector analysis. Methods: In this retrospective study, 171 eyes of 171 patients with cylinder > 1.0 diopters (D) were recruited, with 97 eyes underwent SMILE and 74 eyes underwent TICL implantation. Preoperative and 3-months postoperative visual and refractive results were examined. The astigmatism correction, graded by the degree of preoperative cylinder was compared between two groups using vector analysis. Results: At 3-months postoperatively, the residual cylinder was -0.10 +/- 0.21 D in the SMILE group and -0.30 +/- 0.32 D in the TCL group (p < 0.05). Furthermore, 98% and 85% of eyes had the cylinder within +/- 0.5 D in the SMILE and TICL group, respectively. The vector analysis revealed similar target induced astigmatism vector in two groups. However, the difference vector, magnitude of error, angle of error, and index of success were significantly higher (0.30 +/- 0.32 D, -0.19 +/- 0.25, -2 degrees +/- 4.35 degrees, and 0.16 +/- 0.17 D, respectively) in the TICL group than the values in the SMILE group (0.10 +/- 0.21 D, -0.05 +/- 0.20, -0.03 degrees +/- 2.13 degrees, and 0.05 +/- 0.12, respectively), regardless of the degree of preoperative cylinder (all p < 0.05). For preoperative cylinder < 2.0 D, surgically induced astigmatism vector and correction index in the SMILE group were higher than those in the TICL group (p < 0.05). Conclusion: Both SMILE and TICL implantation are effective techniques for myopic astigmatism correction. However, the accuracy of correction in the magnitude and axis of astigmatism with SMILE was better than that achieved with TICL implantation.