Background The novel dynamic biomechanical device Corvis ST can measure a variety of corneal deformation parameters and record the dynamic process of cornea deformation.Understanding various corneal deformation parameters is of important clinical significance for morphological and functional prediction for myopic eyes in corneal refractive surgery.However,the range and meaning of corneal deformation parameters in myopic eyes are still unknown.Objective This study was to establish the range of corneal defamation parameters by Corvis ST and explore its clinical significance in myopic eyes.Methods A descriptive study was designed under the approval of Ethic Committee of Tianjin Eye Hospital and informed consent of patients.This study protocol complied with Helsinki Declaration.Four hundred and seventy-seven eyes of 257 myopic patients who were going to receive corneal refractive surgery were included in Tianjin Eye Hospital from June 2014 to January 2015.The corneal deformation parameters including the first applanation time (1st A-time),first applanation lengh (1 st A-length),first applanation velocity (1 st A-velocity),second applanation time (2nd A-time),second applanation length (2nd A-length),second applanation velocity (2nd A-velocity),highest concavity time (HC-time),highest concavity deformation amplitude (HC-DA),highest concavity peak distance (HC-PD),highest concavity radius (HC-R),non-contact intraocular pressure (IOPnct) and the central corneal thickness (CCTst) were measured by Corvis ST.Corneal structural parameters including CCT and corneal curvature were measured by 3-D anterior segment analysis system (Pentacam),and corneal biomechanical parameters including corneal resistance factor (CRF),corneal hysteresis (CH),intraocular pressure mimic Goldmann (IOPg) and intraocular pressure of corneal compensation (IOPcc) were measured by Ocular Response Analyzer (ORA).The distributions of the data were tested with the Shapiro-Wilk test and 95％ confidence intervals (CI) were calculated.The correlations of the variables were evaluated by Pearson correlation coefficient and Spearman rank correlation coefficient.Multiple linear regression was used to analyze the changes of 1st A-time,2nd A-time and HC-DA with corneal morphology and biomechanical parameters.Resnlts Only 1st A-time,2ndA-time,HC-time,HC-DA,CCTst and IOPnct showed the normality distribution in corneal deformation parameters.The positive correlations were found between 1st A-time,1st A-length,2nd A-length,2nd A-velocity,HC-R with CCT (r=0.338,rs=0.129,rs=0.282,rs =0.374,r=0.306,all at P＜0.01),while 1st A-velocity,2nd A-time,HC-D and HC-PD showed the negative correlations with CCT (rs =-0.235,r=-0.130,r=-0.259,r=-0.226,all at P＜0.01).CRF and CH showed positive correlations with 1st A-time,2nd A-length,2nd A-velocity,HC-time,HC-R and negative correlations with HC-PD,△A-length (all at P＜0.05).1st A-time,2nd A-time and HC-DA changed with CRF and IOPcc with the regression formations of 1st A-time =6.185+0.066CRF+0.034IOPec (F=300.123,P =0.000),2nd A-time=23.397-0.074IOPec-0.044CRF (F=227.979,P=0.000) and HC-DA =1.523-0.017IOPcc-0.017CRF (F=152.662,P=0.000).The CCTst,IOPst and IOPnct values by Corvis ST were significantly lower than CCT by Pentacam ([548.23±26.31] μm,IOPg ([15.02±2.72]mmHg and ([16.02-±2.56]mmHg) by ORA respectively (t =11.00,2.919,6.815,all at P ＜ 0.01).Conclusions The corneal deformation parameters by Corvis ST can quantitatively describe corneal biomechanical properties in myopic eyes.Both IOP and the corneal steep curvature of the 3 mm center area (K2) affect the deformation response of cornea.The reliability of Corvis ST in the measurement of CCT and IOP remains to be further studied.%背景 Corvis ST生物力学眼压测量仪(Corvis ST)可测得角膜形变的参数,同时可记录角膜受力时的动态变化过程,对近视眼行角膜屈光手术前后角膜结构和功能的预测具有重要的临床意义,但单纯近视眼角膜各形变参数的测定值范围及意义有待研究. 目的 利用Corvis ST测量近视眼角膜形变参数值范围并分析其临床意义,为角膜屈光手术的术前筛查及术后稳定性、安全性的预测等提供参考.方法 采用描述性研究方法,纳入2014年6月至2015年1月在天津市眼科医院拟行角膜屈光手术的单纯近视眼患者257例477眼,所有受检眼均采用Corvis ST测定角膜形变参数,包括第1次压平时间(1stA-time)、角膜长度(1stA-length)和压平速度(1stA-velocity),第2次压平时间(2ndA-time)、角膜长度(2ndA-length)和压平速度(2ndA-velocity),产生最大压陷的时间(HC-time)和最大压陷时的变形幅度(HC-DA)、峰距(HC-PD)、反向曲率半径(HC-R),非接触式眼压(IOPnct)和中央角膜厚度(CCTst);用Pentacam三维眼前节分析诊断系统(Pentacam)检查受检眼结构参数CCT和角膜曲率;用眼反应分析仪(ORA)测定受检眼角膜生物力学参数,包括角膜阻力因子(CRF)、角膜滞后量(CH)、模拟Goldmann眼压(IOPg)和角膜补偿眼压(IOPcc).对上述参数值行Shapiro-Wilk正态性检验并计算各参数总体均值的95％可信区间(CI);用Pearson线性相关分析或Spearman秩相关分析法对角膜形变参数与角膜结构参数及角膜生物力学参数的相关性进行分析;采用多元线性回归法分析1stA-time、2nd A-time和HC-DA随着各角膜形态学及角膜生物力学参数的变化. 结果 角膜形变参数中仅1stA-time、2nd A-time、HC-time、HC-DA、CCTst和IOPnct服从正态分布;1stA-time、1stA-length、2ndA-length、2ndA-velocity、HC-R与CCT值间均呈正相关(r=0.338、rs=0.129、rs=0.282、rs=0.374、r=0.306,均P＜0.01),而1stA-velocity、2ndA-time、HC-DA及HC-PD与CCT均呈负相关(rs=-0.235、r=-0.130、r=-0.259、r=-0.226,均P＜0.01).CRF和CH与1stA-time、2ndA-length、2ndA-velocity、HC-time、HC-R均呈正相关(均P＜0.05),而与HC-PD、△A-length均呈负相关(均P＜0.05).1stA-time、2nd A-time和HC-DA均随着CRF和IOPcc改变发生变化,回归方程分别为1stA-time=6.185+0.066CRF+0.034IOPcc(F=300.123,P=0.000)、2ndA-time=23.397-0.074I0Pcc-0.044CRF(F=227.979,P=0.000)和HC-DA=1.523-0.017IOPcc-0.017CRF(F=152.662,P=0.000).Corvis ST测得的CCTst值、IOPst值和IOPnct值均明显低于Pentacam测得的CCT[(548.23±26.31) μm]和ORA测得的IOPg值[(15.02±2.72) mmHg](1 mmHg =0.133 kPa)和IOPcc值[(16.02±2.56) mmHg],差异均有统计学意义(t=11.00、2.919、6.815,均P＜0.01).结论 Corvis ST测定的单纯近视眼的角膜形变参数可客观定量描述角膜生物力学特性,IOP及角膜3 mm区陡中心曲率(K2)均可影响角膜的形变反应,Corvis ST在测量CCT及IOP方面的可信度有待进一步研究.
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