Repeatability of intra-ocular pressure and central corneal thickness measurements provided by a non-contact method of tonometry and pachymetry

Abstract

To examine the repeatability of intra-ocular pressure (IOP) and central corneal thickness (CCT) measurements provided by the Tono-Pachymeter NT530P (Nidek, Japan), and to assess agreement of the device with Goldmann applanation tonometry (GAT) and ultrasound pachymetry (UP). Sixty-two normal eyes of 62 subjects were included in the study. Three sessions of measurements, each consisting of three sets of measurements, were completed with each device. Repeatability was determined with the coefficient of variation (CoV) and the coefficient of repeatability (CoR) values. Agreement between devices was examined by Bland-Altman analysis and intraclass correlation coefficient (ICC) analyses. The CoV and CoR for IOP values were 18.4% and 5.5mmHg with the NT530P and 16.6% and 4.3mmHg with the GAT respectively. On average, NT530P overestimated the IOP compared with GAT by 1.3mmHg. The 95% limits of agreement between the methods ranged from -5.9 to +3.3mmHg, and the ICC for average IOP measures between devices was 0.64 (P < 0.001). The CoV and CoR for CCT measurements were 5.5% and 59.8μm with the NT530P and 5.5% and 60.5μm with UP. NT530P CCT readings were on average 13μm thinner than those obtained with UP. The 95% limits of agreement (LoA) ranged from -7.4 to +33.1μm, and the ICC for average CCT measures between devices was 0.93 (P < 0.001). The NT530P demonstrated high IOP and CCT measurement repeatability in the normal population studied. The device tended to slightly overestimate IOP compared to GAT. CCT values provided by NT530P were interchangeable with those of UP.