Influence Of Angle Kappa On Postoperative Coma And Visual Quality After Ray-Tracing-Guided Fs-Lasik With Vertex-Centered Ablation

To investigate whether angle kappa (angle κ) modulates the relationship between postoperative coma and visual quality after ray-tracing-guided femtosecond laser-assisted in situ keratomileusis (FS-LASIK) with vertex-centered ablation.

Tianjin Aier Eye Hospital, Tianjin, China.

This retrospective observational study included 60 eyes undergoing ray-tracing-guided FS-LASIK using the WaveLight EX500 platform (Alcon, Germany). Angle κ was quantified as pupil offset, defined as the distance between the entrance pupil center and the corneal vertex. Eyes were divided into small (≤0.20 mm, n = 30) and large (≥0.20 mm, n = 30) angle kappa groups. At 3 months postoperatively, corneal and ocular higher-order aberrations, contrast sensitivity, point spread function metrics, refractive outcomes, and night vision symptoms were evaluated. Correlation and interaction analyses were performed to determine whether angle kappa influenced the association between postoperative coma and visual quality.

Refractive predictability and safety indices were comparable between groups (P > 0.05). The large angle κ group exhibited higher coma and greater increase in coma postoperatively compared with the small angle κ group in both 4-mm an 6-mm optical zones (P < 0.05). Eyes with a larger angle κ along the horizontal (X) axis demonstrated a significantly greater increase in horizontal coma, whereas those with a larger vertical (Y-axis) offset exhibited a more pronounced increase in vertical coma (P < 0.05). Despite this increase, contrast sensitivity, point spread function parameters, and night vision symptoms did not differ significantly between groups (P > 0.05).

Although ray-tracing-guided FS-LASIK with compensation for large angle kappa results in greater measured coma, this increase does not translate into inferior visual quality. Angle kappa significantly modulates the functional impact of postoperative coma, suggesting that aberrations quantified in a pupil-centered reference system may not fully reflect the visual axis-dependent optical performance. These findings highlight the axis-dependent nature of postoperative aberration assessment and provide a potential explanation for the dissociation between measured coma and subjective visual quality in eyes with large angle kappa.