Corneal higher-order aberrations following small incision lenticule extraction for high myopic astigmatism correction

AIM: To compare the visual outcomes and corneal higher-order aberrations (HOAs) of patients with high or low myopic astigmatism after small incision lenticule extraction (SMILE). METHODS: A total of 157 eyes of 157 patients who underwent SMILE were included in this retrospective, nonrandomized, comparative study. All the eyes which were with the rule astigmatism were divided into high astigmatism group (HAG; astigmatism <=-2.00 D, 73 eyes) and low astigmatism group (LAG; astigmatism >=-1.00 D, 84 eyes). Visual and refractive examinations were performed, HOAs of the anterior surface, posterior surface, and total cornea of the eyes were evaluated preoperatively and 6mo postoperatively. RESULTS: At the postoperative 6-month follow-up, uncorrected distance visual acuity of 20/20 or better was achieved in 97% and 100% eyes in HAG and LAG respectively and 74% and 100% eyes were within-0.50 D. Vector analysis revealed no significant differences in the correction index (P=0.066), angle of error (P=0.091) or flattening index (P=0.987) between two groups. The magnitude of error was-0.37 +/- 0.31 D in HAG and-0.04 +/- 0.19 D in LAG (P<0.001). Index of success (IOS) was 0.22 +/- 0.09 in the HAG and 0.50 +/- 0.46 in the LAG (P<0.001). HOAs of most anterior, posterior and total cornea significantly increased after SMILE, especially the spherical aberration and coma. For HAG, the SMILE procedure induced significantly higher anterior, posterior and total cornea horizontal coma and total corneal total HOAs compared with LAG (P<0.001) and these surgically induced HOAs predominantly originated from the anterior surface of the cornea. CONCLUSION: SMILE surgery induces more HOAs and a mild under-correction of astigmatism in eyes with high astigmatism. The increment in HOAs after SMILE is related to preoperative astigmatism.