Residual Astigmatic Error After SMILE for Myopic Astigmatism: Vector, Corneal Aberration, and Topographic Disparity Analyses

Purpose: To evaluate the short-term outcomes of small incision lenticule extraction (SMILE) in eyes with higher myopic astigmatism and to characterize residual astigmatic error using Alpins vector analysis, corneal higher-order aberrations, and superior–inferior topographic disparity (TD). Methods: This retrospective study included 232 eyes of 192 patients undergoing SMILE. Eyes were divided according to preoperative cylinder into a lower-astigmatism group (<1.50 D; 116 eyes) and a higher-astigmatism group (≥1.50 D; 116 eyes), with spherical equivalent matched between groups. Visual acuity, manifest refraction, and corneal topography were evaluated preoperatively and at 1 week, 1 month, and 3 months postoperatively. Astigmatic correction was assessed using target-induced astigmatism (TIA), surgically induced astigmatism (SIA), difference vector (DV), correction index (CI), and angle of error (AE). Corneal higher-order aberrations within 4-mm and 6-mm zones and TD magnitude and angle were also analyzed. Results: Both groups achieved favorable and comparable postoperative visual and refractive outcomes (all P>0.05). The higher-astigmatism group had significantly greater TIA and SIA at all postoperative visits (all P<0.0001). From 1 week to 3 months, DV was significantly greater and CI significantly lower in the higher-astigmatism group (all P<0.05), with CI remaining below 1.0, indicating mild undercorrection. AE did not differ significantly between groups at 1 or 3 months (both P>0.05). Neither TD magnitude nor TD angle differed between groups (P=0.7737 and P=0.4543, respectively). Spherical aberration (Z4⁰) within both 4-mm and 6-mm zones was greater in the higher-astigmatism group throughout follow-up (all P<0.01), whereas 4-mm vertical coma (Z3⁻¹) was greater only at 1 week and 1 month (P=0.0011 and P=0.0065, respectively). Conclusions: SMILE provided favorable short-term visual and refractive outcomes in eyes with higher myopic astigmatism. The greater residual vector error in these eyes was characterized predominantly by mild magnitude-related undercorrection rather than increased axis-related error or superior–inferior topographic disparity. Postoperative aberration differences were limited, consisting mainly of greater spherical aberration and transient early vertical coma. Integrating vector, topographic, and optical analyses provides a more comprehensive characterization of residual astigmatic error after SMILE and may inform future optimization of astigmatic correction strategies.