ABSTRACT
Background Corneal refractive surgery has significant effects on corneal biomechanical properties.However,there are few study on large scale population with corneal biomechanical properties in the myopic population before corneal refractive surgery.Objective This study was to evaluate the change of corneal biomechanical properties and influence factors in myopic eyes using ocular response analyzer (ORA).Methods A prospective cohort study was carried out in Beijing Tongren Eye Center from April 2010 to January 2011.Corneal hysteresis (CH) and corneal resistance factor (CRF) were detected using ORA in 1 792 eyes of 896 myopic subjects who were going to receive corneal refractive surgery under the informed consent.According to different spherical equivalent (SE) the eyes were grouped into-0.25-＜-3.0 D group,-3.0-＜-6.0 D group,-6.0-＜-9.0 D group,-9.0-＜-12.0 D group,-12.0-＜-15.0 D group and ≥-15.0 D group and according to different central corneal thickness (CCT),the eyes were grouped into ＜500 μm group,500-＜550 μm group,550-＜600 μm group and≥600 μm group.The CH value and CRF value in different SE groups or different CCT groups were compared,and the factors influencing CH and CRF were analyzed by Pearson correlation analysis.Results The mean CH and CRF value were (9.84±1.52)mmHg (1 mmHg =0.133 kPa) and (10.46±1.71) mmHg,respectively in the myopic eyes.The CH values were (10.35±1.53),(10.07±1.55),(9.81±1.46),(9.71±1.59),(9.35±1.55) and (9.23±1.28) mmHg in the-0.25-＜-3.0 D group,-3.0-＜-6.0 D group,-6.0-＜-9.0 D group,-9.0-＜-12.0 D group,-12.0-＜-15.0 D group and ≥-15.0 D group,respectively,showing a significant difference among the groups (F=20.69,P＜0.01),and the CH values in the-6.0-＜-9.0 D group,-9.0-＜-12.0 D group,-12.0-＜-15.0 D group and ≥-15.0 D group were significantly lower than those in the-6.0-＜-9.0 D group,-9.0-＜-12.0 D group (all at P＜0.01).There was no significant difference in the CRF values among different SE groups (F =0.65,P =0.49).CH and CRF values were increasing with the raise of CCT,with evidently differences among the CCT＜500 μm group,500 μm ≤ CCT＜550 μm group,550 μm≤ CCT＜600 μm group and CCT≥ 600 μm group (CH:F=110.99,P＜0.01;CRF:F =84.35,P＜0.01),and the CH and CRF values were significantly higher in the 550 μm ≤ CCT＜600 μm group and CCT ≥600 μm group than those in the CCT＜500 μm group (all at P＜0.01).CH showed a positive correlation with SE (r =0.24,P＜0.01),and no significant correlation between CRF and SE (r =0.03,P =0.20).The CH and CRF showed the positive correlations with the CCT (r=0.42,0.57,both at P＜0.01).In addition,CH and CRF values increased as the increases of SE,corneal curvature (CC) and CCT values,with the regression equation of CH =-7.87+0.08SE+0.16CC+0.02CCT (R2=0.26,P＜0.01) and CRF=-11.42+0.14CC+0.03CCT (R2=0.34,P＜0.01),respectively.The CH and CRF did not change with the age and gender in the subjects.Conclusions Corneal biomechanical properties including CH and CRF were positively correlated with CCT,CC and SE.
ABSTRACT
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.