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

Background: 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). Methods: 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. Results: The CoV and CoR for IOP values were 18.4% and 5.5 mmHg with the NT530P and 16.6% and 4.3 mmHg with the GAT respectively. On average, NT530P overestimated the IOP compared with GAT by 1.3 mmHg. The 95% limits of agreement between the methods ranged from -5.9 to +3.3 mmHg, and the ICC for average IOP measures between devices was 0.64 (P