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E. J. Rouse, C. J. Roberts, A. M. Mahmoud; The Measurement of Biomechanical Parameters as a Function of Peak Applied Pressure in the Reichert Ocular Response Analyzer. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1247.
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To determine if the biomechanical parameters measured by the Ocular Response Analyzer (ORA) are a function of the characteristics of the applied air pressure curve.
The setup consisted of a commercial ORA with custom software to allow the peak applied air pressure to be manipulated through a graphical user interface created in Matlab. Preliminary testing on 6 eyes was preformed with the ORA at 6 different maximum pressure levels. Each trial involved 3 replicate measurements at each of the programmed maximum pressure values. One trial was taken at each maximum pressure of 500, 400, 300, 200 and 100 arbitrary units. The infrared applanation signal data and air pressure data were stored each corresponding to a specific time value, as well as the output parameters of corneal hysteresis (CH), corneal resistance factor (CRF), and corneal compensated intraocular pressure (IOPcc). Both linear and quadratic regressions were performed on the data from each of the 6 eyes to determine the nature of the relationship between peak air pressure and biomechanical parameter measurement. The R2 values of the linear and quadratic regressions were statistically compared to determine the best-fit.
The comparison of R2 values showed a statistically significant (p<0.05) better fit with a quadratic regression, when compared to linear regression analysis. The nonlinear response of CH and CRF was characterized by a linear increase with increasing peak pressure over the lower range of pressures, which leveled off at the higher peak applied pressures. IOPcc demonstrated an opposite relationship with a decreasing function of peak applied pressure in the lower ranges.
Corneal viscoelastic response is a function of the rate of force application. The current study demonstrates a nonlinear response of the measured parameters as peak pressure is varied. Clinically, it is important that the peak applied pressure is in the higher range to assure that CH, CRF, and IOPcc values are stable.
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