Comparative Evaluation Of Wavelight Topolyzer And Callisto Image-Guided Cyclotorsion Alignment In Fs-Lasik: A Retrospective Study On Astigmatism Correction Outcomes

This study compares the efficacy of WaveLight Topolyzer automatic cyclotorsion tracking and Callisto image-guided manual alignment in femtosecond LASIK (FS-LASIK) for astigmatism correction. Cyclotorsion misalignment is a critical factor affecting refractive surgery outcomes, and different alignment strategies may lead to variations in postoperative residual astigmatism, visual acuity, and vector analysis parameters. By evaluating these two approaches, this study seeks to determine whether manual alignment with an image-guided system provides superior accuracy in refractive outcomes, particularly for patients with unreliable automated tracking.

This was a single-center, retrospective study conducted in a specialized refractive surgery clinic. All procedures were performed by experienced surgeons using a standardized FS-LASIK protocol. The study included patients undergoing FS-LASIK to correct myopic or hyperopic astigmatism, with a six-month postoperative follow-up period. Patient selection was based on strict inclusion and exclusion criteria to ensure the homogeneity of the study population and the reliability of outcome measures.

This study included 159 eyes divided into two groups based on cyclotorsion control. Group 1(n=113) received real-time automatic cyclotorsion compensation using WaveLight Topolyzer Vario(Alcon, USA), while Group 2(n=46) underwent manual alignment with the Callisto image-guided system (Zeiss, Germany). Preoperative imaging was performed with Pentacam HR(Oculus, Germany), and limbal vessel imaging for manual alignment was obtained using IOLMaster700(Zeiss, Germany). Flap creation was done with the VisuMax femtosecond laser (Zeiss, Germany) and excimer laser ablation was performed using the WaveLight EX500. Postoperative evaluations at one and six months included residual astigmatism, visual acuity, and vector analysis using the Alpins method. 

Preoperative cylindrical values were similar between groups (p=0.661). At six months, mean residual astigmatism was lower in Group 2 (-0.19±0.22 D) compared to Group 1 (-0.26±0.24 D), though this difference was not statistically significant (p=0.051). UDVA was significantly better in Group 2 (0.01 ± 0.02 logMAR) compared to Group 1 (0.04±0.07 logMAR, p=0.019).CDVA also showed significant improvement in Group 2 (p=0.006). Vector analysis revealed superior astigmatic correction in the Callisto group, with a lower difference vector and a higher correction index. Both groups achieved excellent refractive predictability, with 100% of eyes within ±0.50 D of the target refraction. Efficiency and safety indices were similar, with no complications.

Both automatic and manual cyclotorsion control achieved excellent FS-LASIK outcomes. However, Callisto image-guided manual alignment provided superior long-term astigmatic correction and visual acuity, though the difference in residual astigmatism was not statistically significant. This is the first study to compare these methods, demonstrating that manual alignment may be a superior option for patients with unreliable automated tracking. These findings suggest that image-guided systems offer a viable alternative to automatic tracking in select cases.