In this study, the ARS method for measuring IOP was evaluated in an in vitro porcine eye model and showed high precision. The ARS method is, to the authors' knowledge, the first to combine simultaneous, continuous sampling of both parameters included in the applanation principle: force and area. Consequently, there is a potential for reducing errors in clinical IOP tonometry.

ABSTRACT.Purpose: To compare intraocular pressure (IOP) measurements by Pascal, ICare and Goldmann applanation tonometry (GAT), to evaluate the effects of central corneal thickness (CCT) and curvature on IOP measurement and to estimate the intra-observer variability. Methods: A prospective, single-centre study of 150 eyes with a wide range of pressures. Six masked IOP measurements ⁄ method; corneal thickness and curvature were studied for each eye. GAT was the reference. Results: IOP Pascal and IOP ICare correlated with IOP GAT (r = 0.91, 0.89). Mean ICare measurement exceeded GAT by 2 mmHg. Pascal measured higher than GAT at low IOPs and lower at high IOPs. For every 10 mmHg increase in IOP above 31 mmHg, Pascal measured 2 mmHg lower than GAT and vice versa. CCT was correlated significantly with IOP GAT (r = 0.23) and IOP ICare (r = 0.43) but not with IOP Pascal (P = 0.12). CCT was correlated with age. In a subgroup (>50 years), ICare and the difference between IOP GAT and IOP Pascal were affected significantly by the CCT, whereas IOP GAT and IOP Pascal were not. Corneal curvature was correlated significantly with IOP GAT (r = )0.27) and IOP Pascal (r = )0.26) but not with IOP ICare (P = 0.60). Intra-observer variability within each set of six measurements was approximately 2 mmHg, irrespective of method. Conclusion: This study showed a reasonable overall correlation and concordance between the IOP obtained with the three instruments. None of the methods were completely independent of the biomechanical properties of the cornea. ICare showed a significant dependency upon CCT, whereas GAT and Pascal showed a significant dependency on corneal curvature. All methods showed intra-observer variability, which leaves room for further improvement of methods.