Reliability of the non-contact tono-pachymeter Tonopachy NT-530P in healthy eyes

Background Non-contact Tonopachy NT-530P (Nidek Co., LTD) provides intraocular pressure (IOP) and central corneal thickness (CCT) measurements. This study assesses the reliability and repeatability of its IOP measurements in young healthy adult subjects. Methods IOP was determined in the right eye of 64 healthy patients using Tonopachy followed by the Canon TX-10 non-contact and Goldmann applanation (GAT) tonometers. Tonopachy IOP measurements were corrected (Tonopachy-C) or not (Tonopachy-NC) by the instrument for central corneal thickness. Central corneal thickness measurements provided by Tonopachy were also used to correlate (Pearson's coefficient) central corneal thickness with the GAT and Canon TX-10 IOPs. Repeatability of Tonopachy and GAT was assessed in the right eye of 31 subjects in two separate sessions one week apart. Differences between pairs of instruments and between sessions were determined using BlandAltman plots. The coefficient of repeatability was calculated as the 95% limits of agreement (LoA) of differences between the two sessions. Results Tonopachy-NC, Tonopachy-C, Canon TX-10 and the Goldmann tonometers showed a mean IOP of 14.62, 15.64, 15.02 and 14.68mmHg, respectively. Tonopachy-NC and Canon TX-10 readings did not differ significantly from the Goldmann (p > 0.05), with close agreement with both tonometers (GAT versus Tonopachy-NC: -3.84 to 3.96mmHg; Goldmann versus Canon TX-10: -4.75 to 4.07mmHg). Tonopachy-C readings differed significantly from Goldmann (mean difference -0.96mmHg, p = 0.001, LoA from -5.09 to 3.17). Coefficients of repeatability were +/- 3.70, +/- 3.14 and +/- 3.33mmHg for GAT, Tonopachy-NC and Tonopachy-C, respectively. Central corneal thickness measured with Tonopachy was 530.42 +/- 34.96m. There was a significant correlation between central corneal thickness and IOP for all tonometers except Tonopachy-C. Conclusions Reasonable agreement was observed between the Goldmann and Tonopachy. This instrument provides reliable and repeatable IOP measurements not influenced by central corneal thickness. The Tonopachy-NC and Canon TX-10 offer similar reliability compared to the Goldmann applanation tonometer in a young normotensive population.