Evaluating the Impact of Angle Kappa on Effective Optical Zone in Kerato-Lenticule Extraction (KLEx) Surgery with Intraoperative Angle Kappa Adjustment

Abstract

Purpose: This study aimed to investigate the influence of preoperative angle kappa on postoperative effective optical zone (EOZ) in KLEx patients with intraoperative angle kappa adjustment.

Methods: This retrospective study included 174 eyes from 89 myopic patients who underwent the KLEx procedure with intraoperative angle kappa adjustments. Preoperative angle kappa (µ) was approximated as the chord distance between the pupil center and corneal vertex. The cohort was divided into two groups: large angle kappa (µ > 0.2 mm, n = 84) and small angle kappa (µ ≤ 0.2 mm, n = 90). EOZ parameters, including EOZ reduction ratio (RR=EOZ/planned optical zone, %), major and minor axis, decentration, and eccentricity, were measured at one month postoperatively. Linear regression analyses were performed to assess the relationships between preoperative angle kappa and postoperative EOZ parameters.

Results: Postoperatively, RR, major and minor axis, decentration and eccentricity did not differ significantly between groups. Univariate linear regression revealed significant but modest negative correlation of angle kappa with RR and minor axis (adjusted R² = 0.05 and 0.03; P = 0.003 and 0.02, respectively). Further, multivariate regression incorporating preoperative spherical equivalent demonstrated that angle kappa was not a significant predictor of EOZ parameters.

Conclusion: In conclusion, our study showed that preoperative angle kappa had minimal effect on EOZ parameters in KLEx surgery when appropriate intraoperative adjustments for angle kappa were implemented.

Keywords: KLEx; angle kappa; effective optical zone.

Figure 1

Distribution of the corneal vertex (CV) relative to the pupil center (PC). Orange spots represent CVs with a chord distance greater than 0.2 mm, whereas blue spots indicate CVs with a chord distance less than 0.2 mm. The positive X-axis is defined as nasal relative to the PC, and the positive Y-axis as superior relative to the PC. Overall, 18.9% of CVs were located in the superonasal quadrant, 8.8% in the superotemporal quadrant, 43.4% in the inferotemporal quadrant, and 28.9% in the inferonasal quadrant.

Figure 2

Linear regression between preoperative SE and RR. A scatter plot illustrating the linear regression between preoperative SE and RR. Each dot represents an individual eye. A more myopic SE is associated with a lower RR%, indicating greater reduction in EOZ in preoperative high myopic eyes.