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Michael Haustein, Eberhard Spoerl, Lutz Pillunat; Correlation of Biomechanic Parameters Measured by Corvis ST (Oculus®) and by Ocular Response Analyzer (ORA, Reichert®). Invest. Ophthalmol. Vis. Sci. 2013;54(15):1626.
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© ARVO (1962-2015); The Authors (2016-present)
To compare a newer device (CorVis ST, Oculus Inc.®) with the standard device (Ocular Response Analyzer (ORA, Reicherts®) in measuring in-vivo corneal biomechanical properties. Additionally, multiple regression analysis is used to evaluate potential influence factors (e.g. IOP, K-value, corneal thickness (CCT), axial length (AL), anterior chamber depth (ACD)).
65 eyes of 65 normal subjects were included in this prospective, randomized, observational study. Measurements by ORA, Corvis, Pentacam and IOL-master were randomly taken in all participants. Biomechanical parameters were taken by ORA: corneal hysteresis (CH) and corneal resistant factor (CRF) and by CorVis ST: deformation amplitude (DA), radius (R), and wing-distance (WD). Intraocular pressure was measured by GAT, ORA and Corvis. Pentacam (CCT, ACD) and IOL-Master (AL, K-value) were used to quantify anatomical status. SSPS®: T-test, intaraclass correlation coefficient, Pearmans correlation and multiple linear regression analysis were used for statistics.
CH correlates very poor to all parameters of CorVis ST (DA, R, WD), r<0.1. Also, there is no significant correlation to CCT, ACD, and AL. CRF shows a significant correlation to CorVis ST parameters (DA: p=0.02; r=-0.35/R:p=0.016; r=0.36) and to CCT by Pentacam (p=0.001; r=0.526). However, there is no significant correlation to WD, AL, and ACD. DA depends negatively on CRF (p=0.02; r=-0.348), IOP (p<0.001; r=-0.611) and CCT (p=0.011; r=-0.442), but only IOP is a significant influence factor of DA in multiple linear regression analysis (p=0.026; r=0.75) [CRF: p=0.402; CCT: p=0.731].
CorVis ST and ORA are two useful devices to measure corneal biomechanics in vivo. As known, CH represents viscoelastic properties of corneal matrix and CRF dumping properties of the cornea. Therefore, CRF is a degree of elastic resistance. Due to lack of correlation between CH and CorVis parameters and also significant correlation between CRF and DA CorVis measures more corneal dumping properties, probably corneal stiffness or rigidity. However, DA depends on IOP, CRF, and CCT. Therefore, our results support the biomechanical model/equation of Friedenwald: F= (E*CCT*b*DA)/l + IOP*10^(K*V)*A
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