Dynamic contour tonometry vs. non-contact tonometry and their relation with corneal thickness

Abstract

The purpose of this study is to evaluate the concordance between intraocular pressure (IOP) values obtained with a dynamic contour tonometer (DCT) and a non-contact tonometer (NCT) in healthy patients and to investigate the effect of central corneal thickness (CCT) on IOP readings for each of the two measuring systems. The mean IOP yielded by DCT, NCT and corrected non-contact tonometer (CNCT) was 17.1mmHg, 15.5mmHg and 12.2mmHg, respectively. The average CCT was 563.6μm and the ocular pulse amplitude (OPA) was 2.8mmHg. There was a moderate correlation between CCT and CNCT (r=0.34, p=0.001), a weak correlation between CCT and DCT (r=0.03, p=0.788) and a weak-to-moderate correlation between CCT and NCT (r=0.27, p=0.11). The intra-class correlation coefficient (ICC) was 0.59 for the DCT-vs.-NCT comparison and 0.56 for DCT-vs.-CNCT. The mean difference between the two instruments (DCT/NCT) ranged from 1.62 to 4.47mmHg. We have shown that non-contact tonometer is significantly more affected by the central corneal thickness than the dynamic contour tonometer and therefore these methods are not interchangeable.