Postoperative changes in intraocular pressure and corneal biomechanical metrics Laser in situ keratomileusis versus laser-assisted subepithelial keratectomy.

PURPOSE: To compare intraocular pressure (IOP) and corneal biomechanical metric changes after myopic laser in situ keratomileusis and laser-assisted subepithelial keratectomy (LASEK).

SETTING: Private practice, St. Louis, Missouri, USA.

METHODS: The IOP, corneal biomechanical markers, and Ocular Response Analyzer (ORA) waveform parameters were prospectively measured preoperatively and after 6 months in ablation-matched myopic LASIK eyes (mLASIK group) and LASEK eyes (mLASEK group). A retrospectively identified cohort of low myopia LASIK eyes (lmLASIK group) and fellow unoperated eyes (control) were tested at a single postoperative visit. Statistical analysis compared the percentage change in parameters between groups.

RESULTS: The mean postoperative Goldmann tonometry and Goldmann-correlated IOPs were statistically significant reduced in the mLASIK and mLASEK groups (P<.03). Corneal-compensated IOP, but not Pascal dynamic contour tonometry, was significantly reduced in the mLASIK group. The percentage change in corneal hysteresis (CH) and the corneal resistance factor (CRF) was greater in the mLASIK and mLASEK groups than in the lmLASIK group. The greatest percentage change in ORA signal parameters was in the mLASIK group and the smallest change, in the mLASEK group. On multivariate linear regression, the residual stromal bed was predictive of the percentage change in CH and CRF (P<.001).

CONCLUSIONS: Microkeratome flap creation combined with deeper stromal ablation had the greatest effect on the ORA applanation signal, indicating corneas that are more readily deformable. The smallest change in the signal was in the group without a stromal flap (LASEK). There was a complex interaction between ablation location and depth that affected corneal biomechanical properties.