Biomechanical Consequences Of Posterior Corneal Astigmatism-Associated Ablation In High Astigmatism Undergoing Ray-Tracing-Guided Lasik

To prospectively compare the optical and biomechanical outcomes of ray-tracing–guided LASIK (RT-LASIK) and topography-guided LASIK (TP-LASIK) in eyes with high astigmatism, and to determine whether posterior corneal astigmatism (PCA) contributes to differential biomechanical responses following asymmetric ablation.

Tianjin Aier Eye Hospital, Tianjin, China.

In this prospective comparative study, 60 eyes with manifest corneal astigmatism ≥ 2.50 D were enrolled and assigned to RT- or TP-LASIK (30 eyes each, Alcon, Germany). Within each group, 10 eyes had PCA > 0.75 D (ranging from 0.80 D to 1.20 D) aligned with the anterior astigmatism axis. Corneal biomechanics were assessed preoperatively and at 1, 3, and 6 months postoperatively using Corvis ST. Parameters analyzed included Stress-strain index (SSI), SP-A1 and deformation amplitude ratio (DA ratio). Optical quality was evaluated using contrast sensitivity and OPD-Scan III.

All eyes achieved postoperative UDVA ≥20/20 with no clinically significant residual refractive cylinder. RT-treated eyes demonstrated superior contrast sensitivity at spatial frequencies of 6.0-18.0 cpd and higher Strehl ratio. In eyes with PCA < 0.50 D, postoperative SSI, SP-A1, and DA ratio showed no significant differences between RT and TP at any time point (all P > 0.05). However, in eyes with PCA > 0.75 D, RT-treated eyes exhibited progressive reductions in SSI from 0.95 ± 0.02 preoperatively to 0.76 ± 0.09 at 6 months post-operatively, and SP-A1 from 118.50 ± 7.67 to 78.12 ± 8.18. DA ratio increased from 4.00 ± 0.21 to 5.34 ± 0.43. These changes were significantly greater than those observed in TP-treated eyes (all P < 0.05).

In high astigmatism with substantial and axis-aligned PCA contribution, RT-LASIK may introduce greater asymmetric ablation, resulting in more pronounced postoperative biomechanical alteration compared with TP-LASIK treatment. Although RT-LASIK achieved superior optical quality metrics, this advantage was accompanied by measurable biomechanical compromise in this specific subgroup.