Comparative corneal biomechanical changes after FS-LASIK and orthokeratology

The aim of this study was to investigate changes in corneal biomechanical properties after femtosecond laser in situ keratomileusis (FS-LASIK) and orthokeratology (Ortho-K).

In this retrospective comparative study, patients were divided into an Ortho-K group (37 eyes) and a LASIK group (35 eyes) based on whether they underwent Ortho-K correction or FS-LASIK surgery. Keratometry measurement (Km), spherical equivalent (SE), non-contact tonometry (NCT), central corneal thickness (CCT), corneal hysteresis (CH), and corneal resistance factor (CRF) were assessed at baseline and 1 month after treatment (Ortho-K or LASIK).

No significant baseline differences existed between the two groups. After correction, the LASIK group showed significantly lower values in Km, SE, CCT, NCT, CH, and CRF compared to the Ortho-K group (all P < 0.05). Intragroup comparisons revealed significant postoperative reductions in the LASIK group for CCT (from 543.37 ± 36.75 µm to 476.80 ± 38.75 µm, P < 0.001), CH (from 10.68 ± 1.46 mmHg to 9.03 ± 1.52 mmHg, P < 0.001), and CRF (from 10.18 ± 1.89 mmHg to 7.68 ± 1.89 mmHg, P < 0.001). In the Ortho-K group, CH and CRF decreased significantly (CH: 10.98 ± 1.43 to 9.81 ± 1.19 mmHg, P = 0.005; CRF: 10.77 ± 1.70 to 9.42 ± 1.52 mmHg, P < 0.001), but CCT change was insignificant. Analysis of ORA signals confirmed a greater biomechanical impact after LASIK, with significant reductions in both P1 and P2 (both P < 0.001), compared to only a P1 reduction in the Ortho-K group (P = 0.033).

Although both FS-LASIK and Ortho-K reduce CH and CRF values as measured by the ORA, their clinical implications are fundamentally different. The changes induced by FS-LASIK represent a true biomechanical weakening of the cornea, whereas the reductions observed after Ortho-K are primarily measurement artifacts caused by alterations in corneal curvature. Consequently, a more comprehensive approach is required for accurately assessing the corneal biomechanical status following Ortho-K.