Corneal biomechanical measurements before and after laser in situ keratomileusis

PURPOSE: To study the correlation between corneal biomechanical properties and surgical parameters in myopic patients before and after laser in situ keratomileusis (LASIK). SETTING: UCLA Laser Refractive Center of the Jules Stein Eye Institute, Los Angeles, California, USA. METHODS: In 43 eyes of 43 patients, the Ocular Response Analyzer was used to measure corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg), and corneal-compensated IOP (IOPcc) before and 1 month after LASIK. Manifest refraction spherical equivalent (MRSE), preoperative central corneal thickness (CCT), flap thickness (FT), and ablation depth (AD) were also recorded. Changes in these parameters after LASIK were calculated and the correlations between the change in CH (Delta CH), change in CRF (Delta CRF) and the AD, change in MRSE (Delta MRSE), and CCT were examined. The relationship between Delta CRF and Delta MRSE was examined by linear regression analysis. RESULTS: The preoperative mean CH and mean CRF (11.52 mm Hg +/- 1.28 [SD] and 11.68 +/- 1.40 mm Hg, respectively) were significantly higher than postoperative values (9.48 +/- 1.24 mm Hg and 8.47 +/- 1.53 mm Hg, respectively) (P<.0001). A higher attempted correction was correlated with a larger Delta CH and Delta CRF (AD, r = 0.47 and r = 0.65, respectively; Delta MRSE, r = 0.51 and r = 0.66, respectively). No correlation was found between Delta CH, Delta CRF, and preoperative CCT. CONCLUSIONS: Changes in CH and CRF after LASIK suggest alteration in corneal biomechanics correlating with attempted correction. The CRF parameter may be more useful than the CH parameter in assessing biomechanical changes resulting from LASIK.