Distribution of Angle Alpha and Angle Kappa Chord Magnitude and Axes in Myopic and Hyperopic Refractive Surgery Candidates.

Abstract

Purpose: To evaluate the distribution of angle alpha and angle kappa chord magnitudes, axes, and coordinates in myopic and hyperopic refractive surgery candidates.

Methods: A total of 479 eyes were included and divided into myopic and hyperopic groups. Angle alpha and angle kappa chord magnitudes, chord axes, and coordinates were measured for both groups from the Galilei topographer (Ziemer Group) in addition to spherical equivalent refraction (SE) and refractive cylinder. Angle alpha and angle kappa parameters and distribution patterns were compared between groups and correlations with SE and cylinder were analyzed.

Results: Angle alpha and angle kappa chord magnitudes were significantly larger in the hyperopic group (alpha: 0.52 ± 0.12 mm; kappa: 0.34 ± 0.12 mm) compared to the myopic group (alpha: 0.38 ± 0.12 mm; kappa: 0.23 ± 0.12 mm). All angle alpha chord axes and the majority of angle kappa chord axes were in the 90° to 180° and 180° to 270° quadrants, with a strong concentration in the 135° to 225° quadrant (angle alpha: 100% for hyperopia and 94% for myopia; angle kappa: 82.7% for hyperopia, 59.4% for myopia). Angle alpha x-component exhibited a positive correlation with hyperopic SE and a negative correlation with myopic SE. There was no correlation between angles alpha and kappa chord magnitudes and cylinder in both groups.

Conclusions: Angle alpha chord magnitude is larger and has more consistent axis distribution than that of angle kappa. Chord magnitudes of both angles are larger in hyperopia and have stricter axis distribution compared to myopia. Understanding these relationships is key in planning laser and lens-based refractive procedures. [J Refract Surg. 2025;41(6):e585-e593.].