Intra-Session Repeatability and Agreement of Easyton Tonometry with Goldmann, Non-Contact, and Rebound Tonometry in Normal-Tension Glaucoma

Purpose: This study evaluated the intra-session repeatability of the Easyton® transpalpebral tonometer and assessed inter-device agreement among Goldmann applanation tonometry (GAT), non-contact tonometry (NCT), rebound tonometry (RBT), and Easyton in eyes with normal-tension glaucoma (NTG). Methods: This retrospective study included 13 patients (22 eyes) with NTG who underwent intraocular pressure (IOP) measurement during a single visit using NCT, GAT, RBT, and Easyton. The measurement sequence followed fixed clinical flow (NCT → GAT → RBT → Easyton). The three individual Easyton readings were used for the repeatability analysis, whereas device-specific means of three readings were used for the agreement analyses. Intra-session repeatability was assessed using two-way mixed-effects, absolute-agreement intraclass correlation coefficients (ICCs) and within-subject variability indices. Agreement between GAT and each device was evaluated by Bland-Altman analysis, and proportional bias was assessed by linear regression of inter-device differences on mean IOP. Results: Mean IOP (mmHg) was 12.32 ± 2.70 with GAT, 15.27 ± 2.73 with NCT, 13.61 ± 2.21 with RBT, and 15.56 ± 1.99 with Easyton. Easyton demonstrated good intra-session repeatability (ICC, 0.854 for single measures; 0.946 for the average of three), with within-subject SD of 0.80 mmHg and coefficient of repeatability of 2.21 mmHg. Bland-Altman mean differences (GAT - device) were -2.95 mmHg (vs. NCT), -1.30 mmHg (vs. RBT), and -3.24 mmHg (vs. Easyton), with 95% limits of agreement for GAT vs. Easyton of -7.45 to 0.96 mmHg. For GAT vs. Easyton, the proportional bias slope was 0.37 (95% confidence interval [CI], -0.07 to 0.81; p = 0.09). Conclusions: In NTG eyes, Easyton showed good intra-session repeatability and measured higher IOP than GAT on average. It may be useful for repeated IOP measurements within a single visit, but its limited agreement with GAT does not support direct interchangeability. Its suitability for longitudinal IOP monitoring remains to be established.