Effect of Asymmetric Corneal Curvature on Optical Zone Decentration and Refractive Outcomes in SMILE for Myopic Astigmatism

PURPOSE: To investigate the effect of asymmetric corneal curvature on refractive outcomes and optical zone decentration at a 2-year follow-up after small incision lenticule extraction (SMILE) for myopic astigmatism. METHODS: In this prospective study, 96 patients (169 eyes) with myopia and astigmatism (low astigmatism group [cylinder <-2.00 diopters (D)], 91 eyes; high astigmatism group [cylinder >=-2.00 D], 78 eyes) were treated using SMILE. Twoyear postoperative refractive outcomes and optical zone decentration were analyzed and compared between the groups. RESULTS: Both groups achieved good visual and refractive outcomes. The mean postoperative cylinder in the low astigmatism group was significantly lower than that in the high astigmatism group (P < .05). The mean decentration in the low astigmatism group was lower than that in the high astigmatism group (P < .05). In the low astigmatism group, a weak positive correlation was observed between target induced astigmatism (TIA) and the arithmetic mean of angle of error (|AE|), difference vector (DV), and the arithmetic mean of magnitude of error (|ME|). Additionally, a weak positive correlation was observed between decentration and both the arithmetic mean of corneal front surface curvature asymmetry indices (|Sif|) and TIA. Within the high astigmatism group, TIA exhibited a weak positive correlation with |AE|, DV, and |ME|. Similarly, decentration demonstrated a weak positive correlation with |Sif|, TIA, DV, and |ME| (all P < .05). CONCLUSIONS: SMILE surgery achieves good long-term refractive outcomes for correcting myopic astigmatism. However, there are still limitations to the accuracy of high astigmatism correction. Asymmetric corneal surface curvature may affect the astigmatism correction and optical zone decentration.