Vector Analysis of High-Astigmatism Correction in Small Incision Lenticule Extraction: A Comparative Study of VisuMax 500 and VisuMax 800

Purpose: Small incision lenticule extraction (SMILE) performed with the VisuMax 500 femtosecond laser has demonstrated excellent efficacy and safety for myopia correction; however, astigmatism correction tends to be undercorrected. The VisuMax 800 femtosecond laser was developed to address these limitations, integrating centration assistance, automated cyclotorsion adjustment, and increased laser speed. This study compared astigmatic correction outcomes between SMILE performed with the VisuMax 500 and VisuMax 800 in eyes with high astigmatism. Methods: This retrospective comparative study included 155 right eyes of 155 patients with preoperative astigmatism ≥ 3.0 diopters (D) who underwent SMILE at a single center between August 2023 and February 2025. Ninety-one eyes were treated with the VisuMax 500 and 64 eyes with the VisuMax 800, with identical surgical parameters in both groups except for the upgraded systems in the VisuMax 800. Vector analysis using the Alpins method was performed at 3 months postoperatively. Results: Residual astigmatism was significantly lower in the VisuMax 800 group (-0.52 ± 0.27 D) than in the VisuMax 500 group (-0.63 ± 0.33 D, P = 0.038). Vector analysis demonstrated superior outcomes in the VisuMax 800 group, including surgically induced astigmatism (3.59 ± 0.63 D vs. 3.31 ± 0.67 D, P = 0.010), correction index (0.96 ± 0.11 vs. 0.90 ± 0.12, P = 0.004), flattening effect (P = 0.008), and flattening index (P = 0.002), difference vector (P = 0.013), angle of error (P = 0.049), index of success (P = 0.006), and magnitude of error (P = 0.012). Conclusion: SMILE performed with the VisuMax 800 provided superior astigmatic correction compared with the VisuMax 500 in highly astigmatic eyes, with lower residual astigmatism and improved vector parameters. These results suggest that integrated centration guidance, automated cyclotorsion adjustment, and enhanced laser speed in the VisuMax 800 contribute to greater refractive accuracy.