IOPcc IOPg GAT P among three IOP measureme nts Preop. 14.31±2.42 14.19±2.54 13.43±2.19 0.205 Postop. 13.64±2.09 10.27±2.26 10.83±2.83 0.000 Percentage change (%) -2.98±17.50 -26.69±14.35 -18.11±19.80 0.000 P between preop. and postop. 0.02 0.000 0.000 To compare the preoperative and postoperative measurement of corneal biomechanical properties and intraocular pressure (IOP) using Goldmann applanation tonometry (GAT) and the ocular response analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY, USA) in eyes undergoing myopic laser in situ keratomileusis (LASIK) using IntraLase femtosecond laser for flap creation and Schwind ESIRIS excimer laser ablation. Materials and Methods Fourty eyes of 20 patients who underwent corneal wavefront-guided LASIK for the treatment of myopia using IntraLase femtosecond laser for flap creation and Schwind ESIRIS excimer laser ablation were enrolled in this study. The IOP and corneal biomechanical markers were prospectively measured preoperatively and 1 month following LASIK. Manifest refraction spherical equivalent (MRSE), central corneal thickness (CCT), ablation depth (AD), mean corneal curvature (K reading) were also recorded. IOP was measured preoperatively and 1 month following LASIK by ORA and GAT. ORA was used to measure corneal hysteresis (CH), corneal resistant factor (CRF), Goldmann-correlated intraocular pressure (IOPg), and corneal-compensated intraocular pressure (IOPcc) preoperatively and 1 month following LASIK. The same technician performed all of the measurements with three consecutive readings, including only good-quality measurements with two distinct peaks. CCT was measured by ultrasonic pachymetry. All statistical analyses were performed with SPSS ver 18.0 (SPSS Inc., Chicago, IL, USA). The paired-t test was used to compare preoperative and postoperative IOP levels measured by GAT and ORA. The statistical significance of preoperative IOP levels among the GAT, IOPg and IOPcc was evaluated using analysis of variance (ANOVA) for multiple comparison. Postoperative IOP measurements and differences between preoperative and postoperative measurements among three IOP measurements were also evaluated using ANOVA. The Pearson correlation analysis was used to verify correlations between preoperative IOP and possible influencing variables, including patient age, sex, preoperative CCT, SE, K, CH, CRF. Postoperative IOP and difference between preoperative and postoperative IOP were evaluated for correlations with the same parameters. Stepwise multiple regression analysis was used to analyze possible parameters affecting IOP levels measured by GAT and ORA. A P-value less than 0.05 was considered statistically significant. Table 3. Changes in intraocular pressure measurements after LASIK Conclusion Changes in biomechanical properties of the cornea and intraocular pressure following corneal wavefornt-guided laser in situ keratomileusis using IntraLase femtosecond laser for flap creation and Schwind ESIRIS excimer laser ablation Eun Ah Kim 1 , Soo Jeong Park 2 , Tae Won Kim 2 , Seong Jae Kim 3 , Ji Woong Lee 4 1 Department of Ophthalmology, Fatima Hospital, Daegu,Korea, 2 Crystal Eye Hospital, Busan, Korea 3 Department of Ophthalmology, Gyeongsang National University School of Medicine, Jinju, Korea 4 Department of Ophthalmology, Pusan National University Hospital, Busan, Korea Purpose Table 4. Results of multiple regression analysis of preoperative IOPcc, IOPg, and GAT when age, gender, preoperative CCT, MRSE, K, CH, CRF were modeled. Table 2. Preoperative and postoperative findings in corneal biomechanical parameters *by stepwise method Table 1. Patient demographics (n=40 eyes) *by stepwise method Corneal wavefront-guided LASIK using IntraLase femtosecond laser and Schwind ESIRIS laser produced marked decline in CH and CRF, which may reflect changes in the viscous and elastic qualities of the cornea. However, IOPcc showed statistically lower variation in IOP measurement than IOPg and GAT. Results Characteristics Value Age (y) 26.25±7.23 (18-42) M/F 4/16 Ablation depth (μm) 98.95±13.50 (74-123) Preop. Postop. P-value between preop. and postop. CCT (μm) 548.63±27.17 493.63±30.84 0.000 MRSE (diopter) -4.37±0.76 -0.14±0.80 0.000 Mean K (diopter) 43.67±0.77 40.49±1.2 0.000 CH (mmHg) 10.89±1.50 8.41±1.19 0.000 CRF (mmHg) 10.47±1.64 7.16±1.33 0.000 After LASIK, there was a reduction in IOP measurement. ORA-corneal compensated (CC) (∆=-0.67±2.07mmHg;p=0.02) ORA-Goldmann (G) (∆=-3.92±2.19mmHg;p=0.000) GAT (∆=-2.6±2.51mmHg;p=0.000) Although a significant difference was found between the preoperative and postoperative IOPcc, IOPg and GAT (P=0.02, P=0.000 and P=0.000 respectively), the percentage change in IOPg (-26.69±14.35) and GAT (-18.11±19.80) were much greater than in the IOPcc (-2.98±17.50). In addition, although there was no statistically significant difference among the preoperative IOPcc, IOPg and GAT (P=0.205), the difference among postoperative IOPcc, IOPg and GAT was statistically significant ( P=0.000). IOPcc IOPg GAT Coefficient S.E. P* Coefficient S.E. p* Coefficient S.E. P* CH -3.205 0.208 0.000 3.039 0.185 0.000 2.417 0.252 0.000 CRF 2.556 0.191 0.000 -2.537 0.201 0.000 -2.216 0.275 0.000 Table 5. Results of multiple regression analysis of postoperative IOPcc, IOPg, and GAT when age, gender, postoperative CCT, MRSE, K, CH, CRF were modeled. IOPcc IOPg GAT Coefficient S.E. P* Coefficient S.E. p* Coefficient S.E. P* CH -3.484 0.035 0.000 -2.797 0.034 0.000 -1.721 0.440 0.000 CRF 2.859 0.031 0.000 3.319 0.030 0.000 2.357 0.393 0.000 Table 6. Results of multiple regression analysis of ∆IOPcc, ∆IOPg, and ∆GAT when age, gender, AD, ∆CCT, ∆MRSE, ∆K, ∆CH, ∆CRF were modeled. ∆IOPcc ∆IOPg ∆GAT Coefficient S.E. P* Coefficient S.E. p* Coefficient S.E. P* ∆ CH -3.135 0.313 0.000 -2.075 0.179 0.000 -2.348 0.503 0.000 ∆ CRF 2.256 0.261 0.000 2.320 0.149 0.000 2.340 0.420 0.000 Table 7. Results of multiple regression analysis of postoperative IOPcc, IOPg, and GAT when age, gender, preoperative CCT, MRSE, K, CH, CRF were modeled. IOPcc IOPg GAT Coefficient S.E. P* Coefficient S.E. P** Coefficient S.E. P** SE 1.105 0.341 0.003 1.023 0.393 0.013 1.116 0.433 0.014 CH -1.583 0.367 0.000 -1.051 0.423 0.018 CRF 1.416 0.337 0.000 1.444 0.388 0.001 CCT 0.040 0.012 0.002 * by backward method, **by stepwise method