Long-term Vector Outcomes of SMILE in Correcting Moderate to High With-the-Rule Astigmatism Under Astigmatism Axis Marked Condition.

Abstract

To evaluate the vector outcomes of small incision lenticule extraction (SMILE) in correcting moderate to high myopic astigmatism under astigmatic axis marked condition. In a prospective, longitudinal, interventional study, 71 eyes (71 patients) that had with-the-rule preoperative cylinder refraction exceeding 1.50 diopters (D) were corrected with the VisuMax femtosecond laser (Carl Zeiss Meditec AG) at Zhongshan Ophthalmic Center. Refractive outcomes and astigmatic vector were evaluated preoperatively and at 1, 3, 6, and 30 months postoperatively. At 30 months postoperatively, the efficacy and safety indexes were 1.04 ± 0.18 and 1.15 ± 0.17, respectively. The magnitude of the surgically induced astigmatism (SIA) (2.13 ± 0.71 D at 1 month [P1m-pre = .018], 2.12 ± 0.72 D at 3 months [P3m-pre = .006], 2.13 ± 0.69 D at 6 months [P6m-pre = .010], and 2.19 ± 0.72 D at 30 months [P30m-pre < .001]) was slightly higher than that of the target induced astigmatism (TIA) (2.07 ± 0.69 D). Only the y-coordinate of the SIA vector had a significant overcorrection compared to that of the TIA vector (P1m-pre = .033, P3m-pre = .011, P6m-pre = .012, P30m-pre < .001). The corrected index (CI = |SIA|/|TIA|) varied from 1.03 ± 0.07 at 1 month to 1.06 ± 0.10 at 30 months, which was higher when correcting moderate astigmatism than when correcting high astigmatism (P = .041) at 30 months postoperatively. SMILE had long-term safety, efficacy, predictability, and stability when correcting moderate to high myopic astigmatism under astigmatism axis marked condition. Meanwhile, a cylinder overcorrection was observed due to the overcorrection of y-coordinate astigmatic power, which implied that the vector adjustment of the cylinder refraction nomogram should be considered. [J Refract Surg. 2020;36(9):585-591.].