Biomechanical properties of the cornea measured by the Ocular Response Analyzer and their association with intraocular pressure and the central corneal curvature

Background: The aim of this study was to investigate the biomechanical properties of the cornea and their association with intraocular pressure (IOP), central corneal thickness (CCT) and the central corneal radius of curvature (Rc). Methods: Eighty‐three eyes were divided into two groups. The biomechanical properties of the cornea were measured in 63 normal eyes and in 20 post‐laser in situ keratomileusis (LASIK) eyes. The IOP, corneal hysteresis (CH) and corneal resistance factor (CRF) were measured by the Ocular Response Analyzer (ORA). The Rc and CCT were measured using the corneal topographer Medmont E‐300 and the Tomey SP‐100 Handy ultrasonic pachymeter. Other parameters measured by the ORA, such as TimeIn and TimeOut, were also studied. Results: A mean corneal hysteresis of 10.8 mmHg and CRF of 10.6 mmHg were recorded for the normal eyes. There was no significant association with central curvature. All parameters measured by the ORA showed a significant correlation with the CCT, except for the corneal‐compensated intraocular pressure (IOPcc). Both IOPs measured by the ORA had the same values for the mean CH and CRF. For the post‐LASIK eyes, the CH and CRF were lower than in the normal non‐operated eyes. The TimeIn and the TimeOut also presented lower values for the post‐LASIK eyes, suggesting that additional data can be obtained with the ORA measurements. Conclusions: The results of this study indicate that there is no correlation between the parameters measured with the Ocular Response Analyzer and central corneal radius of curvature. Some of the biomechanical properties of the cornea studied were found to differ in the normal eyes compared to the post‐LASIK eyes.     

Corneal biomechanical properties in normal‐tension glaucoma

Purpose: To investigate the intraocular pressure (IOP) and corneal biomechanical properties of normal and normal‐tension glaucoma (NTG) eyes. Methods: This study included 83 normal and 83 NTG eyes. We measured corneal‐compensated IOP (IOPcc), Goldmann‐correlated IOP (IOPg), corneal resistance factor (CRF), corneal hysteresis (CH) and central corneal thickness (CCT) three times each for normal and NTG eyes using an Ocular Response Analyzer (ORA). Results: No significant difference in CCT was seen between normal eyes (541.4 ± 26.8 μm) and NTG eyes (535.4 ± 24.9 μm; p = 0.16). IOPcc was significantly higher in NTG eyes (16.1 ± 2.6 mmHg) than in normal eyes (15.1 ± 2.9 mmHg; p = 0.01), while IOPg was significantly lower in NTG eyes (14.1 ± 2.7 mmHg) than in normal eyes (15.1 ± 3.0 mmHg; p = 0.04). CRF and CH were significantly lower in NTG eyes (CRF, 8.9 ± 1.5 mmHg; CH, 9.2 ± 1.3 mmHg) than in normal eyes (CRF, 10.6 ± 1.4 mmHg; CH, 10.8 ± 1.3 mmHg; p < 0.0001 each). Conclusion: IOPcc was significantly higher in NTG eyes than in normal eyes. The ORA may be useful for distinguishing between the IOPcc of NTG eyes with normal IOP and that of normal eyes. In addition, the ORA enables CRF and CH to be measured in vivo, and weakness of the lamina cribrosa may be clinically inferred from the fact that CRF and CH were reduced in NTG eyes in our study. Low CRF and CH may be clues to the pathology of NTG.     

正常角膜及圆锥角膜的生物力学特性比较研究

目的 了解正常角膜和圆锥角膜的角膜滞后量(CH)和阻力因子量(CRF),探讨圆锥角膜形态和结构改变后对角膜生物力学特性的影响.方法 病例对照研究.选取同时期46只圆锥角膜眼作为圆锥角膜组,96只正常角膜眼作为对照组.用眼反应分析仪(ORA)测定两组眼的CH和CRF,并进行比较分析.其中对照组按角膜散光又分为高度散光(≥3.00 D)和中低度散光(<3.00 D);圆锥角膜组按Amsler-Krumeich法分为轻度(Ⅰ级)、中度(Ⅱ级)和重度(Ⅲ/Ⅳ级).对组间CH和CRF差异比较采用t检验或单因素方差分析.CH和CRF与中央角膜厚度,角膜曲率,角膜散光以及后表面高度间进行直线相关和多重回归分析,绘制CH和CRF的接受者工作特征(ROC)曲线.结果 CH和CRF在圆锥角膜组为(7.1±1.6)和(6.3±1.5)mm Hg(1 mm Hg=0.133 kPa),明显低于对照组的(10.1±1.3)和(10.5±1.6)mm Hg(t=-11.813,-14.943;P<0.001),分别下降(3.0±0.3)和(4.2±0.3)mm Hg.CH和CRF在对照组中的高度角膜散光和中低度角膜散光组之间差异无统计学意义(t=0.373,0.095;P>0.05).CH和CRF大小与圆锥角膜病变程度呈负相关(r=-0.627,-0.587;P<0.001).多重线性回归分析中,圆锥角膜组CH与角膜厚度和曲率相关(r=0.320,-0.375;P<0.05),CRF与角膜曲率相关(r=-0.441,P<0.01),而在对照组中两者与角膜厚度显著相关(r=0.367,0.459;P<0.001),与角膜曲率、散光无关(P>0.05).CH与CRF的ROC曲线下面积分别为0.9282和0.9731(Z=20.462,38.305;P<0.0001),两者之间差异有统计学意义(Z=7.134,P=0.008).结论 圆锥角膜的CH和CRF较正常角膜明显降低,尤以CRF更明显.对CH和CRF进行长期随访,有助于评估圆锥角膜的病变进程.CH和CRF可纳入诊断圆锥角膜的辅助检测指标.     

A five-year follow-up study of posterior corneal curvature and central corneal thickness after LASIK using OrbscanⅡ

Objective To study the long-term （five-year follow-up） changes in posterior corneal curvature and central corneal thickness by using the OrbscanⅡ topographer in patients who had undergone laser in situ keratomileusis （LASIK） for myopia. Methods Forty-eight eyes of 48 patients who had undergone LASIK for myopia were included in a retrospective observational case series study. The mean preoperative refractive error was -6.25±2.87 D. The preoperative and postoperative changes in the posterior corneal curvature and central corneal thickness of each eye were measured by OrbscanⅡ. The posterior corneal curvature was obtained from the central 6mm zone of the OrbscanⅡ. The postoperative follow-up period was at 1， 3， 6， 9， 12， 24， 36 and 60 months. Using SPSS 16.0 software， a comparison of the least-significant difference （LSD） pairwise was used to analyze the difference in the posterior corneal curvature and central corneal thickness at each follow-up visit. Results ①The posterior corneal curvature was higher in the 1st month postoperatively compared to preoperative curvature （t=8.211， P<0.01）. There was no statistically significant difference for the change in posterior corneal curvature from the 1st month to the 9th month （P>0.05）. The posterior corneal curvature slowly decreased over time from the 9th month to the 24th month （the values of t were -4.640 and -2.659， the values of P were <0.001 and 0.014）. The posterior corneal curvature did not become stable until after the 24th month （P>0.05）. ②The central corneal thickness was lower in the 1st month postoperatively than preoperative thickness （t=10.08， P<0.01）. The central corneal thickness slowly increased over time from the 1st month to the 9th month （the values of t were -5.402， -4.428 and -2.334， the values of P were <0.001， <0.001 and 0.027）. The central corneal thickness did not become stable until after the 9th month （P>0.05）.③The posterior corneal curvature was correlated with corneal thickness （r=-0.703， P<0.01）. Conclusion The posterior corneal curvature and the central corneal thickness both increase shortly after LASIK surgery and stabilize after this initial period. There is a negative correlation between posterior corneal curvature and central corneal thickness.     

LASIK手术前后角膜生物力学特性的比较

目的比较准分子激光原位角膜磨镶术（LASIK）前角膜阻力因子（CRF）和角膜滞后量（CH）与中央角膜厚度的关系;比较LASIK术前及术后不同时间段角膜的生物力学特性。方法病例对照研究。选取2010年1月至2010年2月在山西省眼科医院要求行LASIK手术的近视患者84例（168眼）。根据角膜厚度为分为A组（550—643μm,67眼）、B组（500—549μm,72眼）、C组（450～499μm,29眼）,用眼反应分析仪（ORA）测定这些术眼的CRF和CH,并进行比较分析。对其中已手术并定期完成12个月随访有完整资料的40例（80眼）患者进行术前及术后不同时间段（术后1、3、6、12个月）角膜生物力学特性的比较分析。采用单因素方差分析法对数据进行统计。结果术前三组的CRF和CH分别为11．11±1．69和10．79±1．48、9．83±1．39和9．87±1．29、9．06±1．96和9．79＋1．76,差异均有统计学意义（F=19．55、8．54,P〈O．01）。40例患者术前及术后各时间段CRF与CH的差异均有统计学意义（F=102．88、60．80,P〈O．011。术后各时间段各组CRF与CH差异均无统计学意义。结论CRF和CH与中央角膜厚度有关,随着角膜厚度的减小而降低。LASIK术后残留角膜基质床厚度为整个角膜厚度的50％以上时,角膜生物力学特性基本稳定,是安全的切削范围。     

The Effect of Pterygium and Pterygium Surgery on Corneal Biomechanics

Purpose: To evaluate the effect of pterygium and pterygium surgery on corneal biomechanics by ocular response analyzer (ORA, Reichert, USA). Methods: This study considered 68 eyes (from 34 patients with a mean age of 21.2±7.1 years) with unilateral nasal, primary pterygium (horizontal length <4 mm), and having undergone pterygium excision and conjunctival autografting. Pterygium length and area were measured from a photograph of the anterior segment using Image J program. ORA measurements were obtained before surgery and after the first month of the surgery. The measurements of the eyes with pterygium and healthy eyes were compared to evaluate the effect of pterygium. Similarly, measurements obtained before and after surgery were compared to evaluate the effect of pterygium surgery on corneal biomechanics. The correlation of the ORA measurements with the pterygium area was evaluated. Results: Mean pterygium horizontal length and area were 3.31±1.43 mm and 6.82±2.17 mm², respectively. There was no statistically significant difference between the eyes with and without pterygium in corneal hysteresis (CH, p=0.442), corneal resistance factor (CRF, p=0.554), corneal-compensated intraocular pressure (IOP_cc, p=0.906), and Goldmann-correlated IOP (IOP_g, p=0.836). All preoperative parameters decreased after surgery; however, none of them were statistically significant (CH, p=0.688; CRF, p=0.197; IOP_cc, p=0.503; IOP_g, p=0.231). There were no correlations between pterygium area and ORA measurements (p>0.05). Conclusion: Pterygium <4 mm and its surgical excision did not affect corneal biomechanics. These results may be taken into account when cornea biomechanics, mainly intraocular pressure measurements, are important.     

翼状胬肉手术后角膜曲率变化及对人工晶状体度数测算的影响

目的　探讨翼状胬肉手术后角膜曲率变化及对人工晶状体度数测算的影响。方法　收集2016年7月至2017年4月于广州医科大学附属第二医院行手术治疗的原发性鼻侧翼状胬肉患者,共32例42眼,设为胬肉组;对照组为胬肉组中单眼翼状胬肉患者的对侧眼,共22例22眼。术前测量胬肉组患者翼状胬肉长度、宽度和面积,同时计算对照组理论人工晶状体度数。在术前及术后1个月、3个月使用IOL Master测量胬肉组患者眼轴长度、前房深度、角膜曲率、理论人工晶状体度数等。结果　胬肉组术前角膜水平曲率为（43.32±1.69）D,术后1个月为（44.30±1.40）D,术后3个月为（44.32±1.43）D。术前角膜平均曲率（44.32±1.32）D,术后1个月为（44.78±1.40）D,术后3个月为（44.73±1.38）D,术后角膜水平曲率和角膜平均曲率均较术前升高（均为P<0.05）,但术后1个月与术后3个月差异均无统计学意义（均为P>0.05）。胬肉组患者术前术后眼轴长度、前房深度、角膜垂直曲率均无明显变化（均为P>0.05）。胬肉组患者术前理论人工晶状体度数为（21.46±1.57）D,术后1个月为（20.84±1.65）D,术后3个月为（20.86±1.64）D。术后理论人工晶状体度数较术前下降,差异均有统计学意义（均为 P<0.01）。根据ROC曲线计算得出,翼状胬肉长度2.15 mm、宽度4.20 mm、面积5.18 mm²为判断翼状胬肉及其手术对人工晶状体度数测算是否有较大影响的最佳诊断界值。结论　翼状胬肉术后角膜水平曲率和角膜平均曲率增加。角膜曲率的改变导致测算的人工晶状体度数下降。当翼状胬肉较大时会对人工晶状体度数测算产生有临床意义的影响。     

角膜塑形术后角膜生物力学属性研究

【摘要】 目的 观察角膜塑形术后1天角膜形态变化和角膜生物力学变化。设计 前瞻性病例系列。 研究对象 等效球镜度-1.50~-6.00 D的青少年近视患者15例（30眼）。方法 双眼配戴夜戴型角膜 塑形镜,配戴前、配戴一夜摘镜时和摘镜后4小时分别测量等效球镜度、Pentacam分析系统测量角 膜平坦、陡峭K值和中央角膜厚度,眼反应分析仪测量角膜生物力学特性。主要指标 等效球镜度, 角膜曲率,中央角膜厚度,角膜黏滞性CH值,角膜阻力因子CRF值。结果 配戴角膜塑形镜一夜后等 球镜效度由配戴前（-3.72±1.82） D下降到（-2.12±1.93） D,角膜曲率平坦K1值从（41.95± 1.12） D下降到（41.22±1.34） D,摘镜4小时后等效球镜度回升到（-2.59±1.98）D,角膜曲率 平坦K1值回升到（41.44±40.10） D。中央角膜厚度在配戴一夜后由（535.9±34.5）μm增加到（ 553.3±36.6）μm（P=0.000）,摘镜4小时恢复至（535.0±40.3）μm。配戴一夜后CRF值由 （10.0±1.4）mm Hg升高至（10.7±1.5）mm Hg（P=0.037）。CH值由（10.6±1.4）mm Hg略有升 高至（10.7±1.3） mm Hg（P=0.208）。摘镜后4小时,与刚摘镜时比CRF值回降至（9.6±1.2）mm Hg（P=0.000）,与配戴前比差异无统计学意义（P=0.148）。CH与配戴后的差异无统计学意义 （P=0.163）。结论 配戴角膜塑形镜后1天角膜生物力学随角膜形态变化而改变,角膜生物力学测 量可作为配戴角膜塑形镜后角膜微观结构变化的一种观察手段。（眼科, 2012, 21： 381-383）     

小切口角膜基质透镜取出术与飞秒激光辅助准分子原位角膜磨镶术对角膜生物力学特性影响的对比分析

目的　比较小切口角膜基质透镜取出术（small-incision lenticule extraction,SMILE）与飞秒激光辅助准分子原位角膜磨镶术（femtosecond laser-assisted laser in situ keratomileusis,FS-LASIK）治疗近视对患者角膜生物力学特性的影响。方法　选取在我院行SMILE和FS-LASIK手术的近视患者共67例134眼。根据手术方式及等效球镜度数（spherical equivalent,SE）的不同将患者分为4组:中度近视SMILE组15例30眼和中度近视FS-LASIK组16例32眼（-3.00 D≤SE＜-6.00 D）;高度近视SMILE组18例36眼和高度近视FS-LASIK组18例36眼（6.00 D≤SE＜-9.00 D）。分别于术前及术后3 d 、10 d、1个月、3个月使用眼反应分析仪ORA测量4组患者角膜滞后量（corneal hysteresis,CH）和角膜阻力因子（corneal resistance factor,CRF）。计算4组患者术后各时间点的CH和CRF改变量,并分别比较中度近视SMILE组和中度近视FS-LASIK组、高度近视SMILE组和高度近视FS-LASIK组CH和CRF改变量的差异。结果　中度近视SMILE组患者△CH在术后3 d（P=0.030）和术后3个月（P=0.030）时均小于中度近视FS-LASIK组。中度近视SMILE组患者△CRF在术后3 d（P=0.000）、10 d（P=0.008）、1个月（P=0.011）、3个月（P=0.001）时均小于中度近视FS-LASIK组。高度近视SMILE组△CH和△CRF在术后3 d、10 d、1个月、3个月时均小于高度近视FS-LASIK组（均为P=0.000）。结论　SMILE与FS-LASIK手术都会引起角膜生物力学稳定性的降低,但SMILE对角膜生物力学变化的影响更小。     

Evaluation of corneal biomechanical properties following penetrating keratoplasty using ocular response analyzer

Purpose:

To evaluate corneal biomechanical properties in eyes that has undergone penetrating keratoplasty (PK).

Materials and Methods:

Retrospective observational study in a tertiary care centre. Data recorded included ocular response analyzer (ORA) values of normal and post-keratoplasty eyes [corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg), and cornea-compensated intraocular pressure (IOPcc)], corneal topography, and central corneal thickness (CCT). Wilcoxon signed rank test was used to analyze the difference in ORA parameter between post-PK eyes and normal eyes. Correlation between parameters was evaluated with Spearman''s rho correlation.

Results:

The ORA study of 100 eyes of 50 normal subjects and 54 post-keratoplasty eyes of 51 patients showed CH of 8.340 ± 1.85 and 9.923 ± 1.558, CRF of 8.846 ± 2.39 and 9.577 ± 1.631 in post-PK eyes and normal eyes, respectively. CH and CRF did not correlate with post-keratoplasty astigmatism (P =0.311 and 0.276, respectively) while a significant correlation was observed with IOPg (P =0.004) and IOPcc (P < 0.001).

Conclusion:

Biomechanical profiles were significantly decreased in post-keratoplasty eyes with significant correlation with higher IOP as compared with that in normal eyes.