# Distribution of static and dynamic cyclotorsion and influencing factors in FS-LASIK

## TL;DR

This study examines cyclotorsion during eye surgery and finds factors affecting its measurement accuracy.

## Contribution

Identifies risk factors for cyclotorsion registration failure and correlations with dynamic cyclotorsion in FS-LASIK.

## Key findings

- Thin corneal flap and high laser cavity temperature increase SCC registration failure risk.
- Age, spherical power, laser temperature, and ablation time correlate with dynamic cyclotorsion amplitude.
- 80.6% of eyes had successful static cyclotorsion registration.

## Abstract

This study evaluated the static cyclotorsion component (SCC) and dynamic cyclotorsion component (DCC) during femtosecond laser-assisted stromal in situ keratomileusis (FS-LASIK) and identified factors influencing these components.

This retrospective cross-sectional study included 196 patients (392 eyes) with refractive errors who underwent bilateral FS-LASIK. The cohort comprised 105 men and 91 women (mean age: 23.88 ± 6.90 years). An IntraLase femtosecond laser machine was used to create the corneal flap, whereas an AMARIS excimer laser machine was used to ablate the corneal stroma. Parameters related to SCC and DCC were collected using an eye tracker, which also calculated the registration success rate. Preoperative and intraoperative variables were analyzed.

Static cyclotorsion was successfully registered in 80.6% of eyes, with corneal flap thickness [odds ratio (OR) = 0.903, p < 0.01] and laser cavity temperature (OR = 1.26, p = 0.047) identified as significant factors associated with registration failure. No significant correlation was found between absolute SCC and preoperative or intraoperative variables (all p > 0.05). For DCC, 98.7% of eyes were successfully registered, with a median amplitude of 1.00 degrees (0.78–1.30 degrees). Spearman’s correlation analysis revealed significant correlations between age, equivalent spherical power, laser cavity temperature, actual ablation time, and DCC amplitude (all p < 0.05).

Thin corneal flap and elevated laser cavity temperature are risk factors associated with SCC registration failure. Age, equivalent spherical power, laser cavity temperature, and actual ablation time were correlated with dynamic cyclotorsion, highlighting the need for precise tracking in FS-LASIK.