Automated Versus Image-Guided Cyclotorsion Control in FS-LASIK: A Vector Analysis Study

Purpose To compare automated cyclotorsion compensation using the WaveLight® Topolyzer™ system with manual cyclotorsion alignment guided by the Callisto image-guided system in achieving accurate astigmatic correction during femtosecond laser–assisted in situ keratomileusis (FS-LASIK).Methods This retrospective, single-center study analyzed data from 159 eyes that underwent FS-LASIK with a 6-month postoperative follow-up. Group 1 (n = 113) received real-time automated cyclotorsion compensation using the WaveLight® Topolyzer™ system, whereas Group 2 (n = 46) underwent manual cyclotorsion alignment guided by the Callisto image-guided system when automated registration was not feasible. Postoperative uncorrected (UDVA) and corrected (CDVA) distance visual acuity, residual refractive astigmatism, and vector analysis parameters—including target-induced astigmatism (TIA), surgically induced astigmatism (SIA), correction index (CI), difference vector (DV), and index of success (IOS)—were evaluated at 1 and 6 months.Results Baseline cylindrical refractive error was comparable between the groups (p = 0.661). At 6 months, mean residual astigmatism was −0.28 ± 0.26 D in Group 1 and −0.19 ± 0.22 D in Group 2, although the between-group difference did not reach statistical significance (p = 0.051). Group 2 achieved significantly better UDVA at 6 months (0.01 ± 0.02 logMAR) compared with Group 1 (0.04 ± 0.07 logMAR; p = 0.019). Vector analysis demonstrated a lower difference vector and a slightly higher correction index in Group 2, indicating more precise long-term astigmatic alignment.Conclusions Both automated and image-guided cyclotorsion control strategies produced excellent visual and refractive outcomes after FS-LASIK. However, image-guided manual alignment using the Callisto system was associated with superior uncorrected visual acuity and a more favorable vector profile, supporting its use as an effective alternative when automated cyclotorsion registration is limited.