Reliability of the Non-contact TONO-i Tonometer Compared with the Goldmann Applanation Tonometer

Abstract

Purpose: The accuracy and agreement of intraocular pressure (IOP) measurements using a noncontact self-measuring tonometer, TONO-i, compared with the Goldmann applanation tonometer (GAT).Methods: A total of 35 healthy participants and 42 primary open angle or normal tension glaucoma patients were enrolled in this study. TONO-i and GAT measurements were obtained and the mean difference in IOPs was analyzed using a paired <i>t</i>-test. IOP agreement was calculated using the two-way random effects model. Bland-Altman analysis and simple linear regression were used to estimate the disagreement between IOP measurements.Results: The mean IOPs measured using the TONO-i and GAT were 15.9 ± 3.3 mmHg and 16.4 ± 5.1 mmHg, respectively. In glaucoma patients, the mean values measured using the TONO-i (16.7 ± 4.1 mmHg) were lower than those measured using the GAT (17.9 ± 6.1 mmHg; <i>p</i> < 0.001). However, there was no significant difference among the healthy participants (<i>p</i> = 0.273). The intraclass coefficients (95% confidence interval) for all participants, normal participants, and glaucoma patients were 0.847 (0.702-0.920), 0.882 (0.804-0.941), and 0.828 (0.742-0.887), respectively, indicating good agreement between the IOP measurements. The mean difference and limits of agreement were not statistically significant. As IOP increased, the absolute difference between the GAT and TONO-i measurements also increased.Conclusions: The TONO-i, a novel tonometer, may be used reliably for IOP self-measurement and detecting IOP elevations. However, caution must be exercised because of the possibility of underestimating high IOPs.