Refractive and Visual Outcomes of Myopic Laser-Assisted In Situ Keratomileusis (LASIK) Centered on the Entrance Pupil Versus 50% of the Pupil-to-Vertex Chord

BackgroundLaser ablation in myopic laser-assisted in situ keratomileusis (LASIK) is most commonly centered on the entrance pupil, yet the pupil center sits temporal to the visual axis, making the corneal vertex a rational alternative.Comparative studies of the two landmarks have produced conflicting results, and although modern platforms allow the ablation to be placed at any fraction of the distance between them, to the best of our knowledge, no study has compared pupil centration against a 50% offset toward the vertex in myopic eyes.This study compared refractive accuracy, astigmatic outcomes, and the efficacy and safety indices of myopic LASIK centered on the entrance pupil versus 50% of the pupil-to-vertex chord. MethodsThis retrospective cohort study included 389 eyes of 211 patients undergoing primary myopic LASIK by a single surgeon with the WaveLight EX500 excimer laser (Alcon Laboratories Inc., Fort Worth, Texas, USA); 192 eyes centered on the entrance pupil; and 197 eyes treated at 50% of the pupil-to-vertex chord (chord mu).Refractive accuracy, residual astigmatism, Alpins vector indices, and efficacy and safety indices were compared at three months using generalized estimating equations clustered on the patient and adjusted for age, sex, and corneal astigmatism. ResultsMean chord mu was 210 ± 109 µm and did not differ between groups.No endpoint favored either strategy: 182/192 (94.8%) versus 183/197 (92.9%) of eyes were within ±0.50 D of target (P = 0.56), residual astigmatism was 0.30 D in both groups (P = 0.27), the efficacy index was 1.00 ± 0.15 versus 0.99 ± 0.16 (P = 0.72), the safety index was 1.05 ± 0.13 in both groups (P = 0.95), and no eye lost two or more lines of corrected acuity.Group differences did not vary with chord mu. ConclusionsIn myopic LASIK, no statistically significant differences in refractive or high-contrast visual outcomes were detected between ablation centered on the entrance pupil and ablation centered halfway toward the corneal vertex.The study was not designed as an equivalence trial, and contrast sensitivity, night vision, and aberrometric outcomes were not assessed, so these findings indicate an absence of detected differences rather than established equivalence.