Assessment of the ocular response analyzer as a tool for intraocular pressure measurement

The ocular response analyzer (ORA) is a new indentation tonometer that subjects the cornea to an increasing then decreasing air pulse, and uses the corresponding two applanation pressures P1 and P2 to estimate the intraocular pressure (IOP). The present study aims to improve the accuracy of IOP estimation through representative numerical simulation of the ORA procedure. A parametric study has been carried out to consider the effect of corneal thickness, curvature, age, and true IOP on the P1 and P2 measurements. Based on the obtained database of input and output parameters, an equation has been suggested relating the P1 and P2 measurements to the value of IOP. The equation is intended to make IOP estimates independent of corneal stiffness, which varies with size and age. The equation has been tested against a clinical data set obtained at Moorfields Eye Hospital involving 144 subjects, and found to produce IOP estimates that are less dependent on corneal size and age than published equations.