The Study On Corneal Biomechanical Property For Normals And Eyes With Corneal Refractive Surgery By Using Ocular Response Analyzer (ora)

Purpose:To investigate the corneal hysteresis (CH) and corneal resistance factor (CRF) in normal eyes and to determine their relationship between other corneal biometric parameters. To compare the corneal biomechanical changes following Epipolis laser in keratomileusis (Epi-LASIK), Laser in situ keratomileus (LASIK) and Sub-Bowman's keratomileusis (SBK) in the early and late stage post corneal refractive surgery.Methods:Section 1:A Cross-sectional study. This study included 480 normal eyes (240 patients). Ocular Response Analyzer (ORA, Reichert Ophthalmic Instruments, New York, USA) and Pentacam (Oculus GmbH, Wetzlar, Germany, software version 1.17r27) were used to measure CH, CRF and other corneal biometric parameters. One-way AN OVA was used for multiple groups'means comparison.Section 2:A prospective study. Early stage group (follow-up time:1 week and 1 to 2 months postoperatively):Epi-LASIK (n=30), LASIK (n=34), SBK (n=22); Late stage group (follow-up time:1 year postoperatively):Epi-LASIK (n=40), LASIK (n=39). ORA and Pentacam were used to measure corneal biometric parameters pre-and post surgery, respectively. Repetitive measure analysis of variance (ANOVA), Independent samples t test, and Pearson correlation coefficient was used for analysis.Results:1. The values of CH and CRF presented normal distribution and the mean CH was (10.38±1.36) mmHg, and the mean CRF was (10.70±1.59) mmHg.2. A good correlation was observed between CH, CRF and CCT (CH:r=0.54, P=0.000; CRF:r=0.61, P=0.000), but no statistical significant correlation was found between CH,CRF and age, spherical equivalent, cylinder equivalent, and mean refractive spherical equivalent. CH and CRF were correlated with central corneal elevation of anterior surface (CH:r=-0.136*, P=0.002; CRF:r=-0.152*,P=0.001) and Q value of anterior surface (CH:r=0.136*, P=0.002; CRF:r=0.132*, P=0.003), positively with corneal spherical aberration (CH:r=0.184*, P=0.000; CRF: r=0.191*, P=0.000) 3. Corneal volume was calculated within diameters from 1.0 to 6.0 mm with 0.5 mm steps centered on the center point to create the corneal-volume distribution. CH and CRF were correlated positively with CV.4. There were no significant differences in CH and CRF between the 3 groups at the early stage postoperatively (CH:F= 0.623, P=0.539; CRF:F=0.038, P= 0.963).5. There were no significant differences in CH and CRF between the 2 groups at the late stage postoperatively (CH:t=-0.270, P=0.308; CRF: t=-0.989, P= 0.630)6. The correlation between ablation depth (AD) and CH, CRF was significant in LASIK group, but not in the other groups.Conclusions:1. The values of CH and CRF presented normal distribution. A good correlation was observed between CH, CRF and CCT, but no statistical significant correlation was found between CH, CRF and age, and MRSE. CH and CRF were correlated positively with CV, and CRF was much more closely related to it.2. CH and CRF were correlated negatively with central corneal elevation of anterior surface, and also correlated negatively with Q value of corneal anterior surface. There was a weak positive correlation between corneal spherical aberration and corneal biomechanical properties.3. There were no significant differences in both CH and CRF between the 3 groups (Epi-LASIK, LASIK, SBK) at the early stage postoperatively. Additionally, there were no significant differences in both CH and CRF between the 2 groups (Epi-LASIK, LASIK) at the late stage postoperatively.4. The correlation between AD and CH, CRF was significant in LASIK group, but not in the other groups, which means, compared with ablation in the more shallow level (Epi-LASIK, SBK), LASIK was more susceptible to ablation depth.