Purpose: To evaluate the congruity of intraocular pressure (IOP) measurements from supine patients, which were obtained using four portable tonometers.
Methods: Intraocular pressure measurements were obtained from the right eye of 72 supine patients. We used the iCare (Tiolat Oy, Helsinki, Finland) rebound tonometer, the Diaton (BICOM Inc., Long Beach, NY) transpalpebral tonometer, the Tonopen XL (Reichert inc., Depew, NY), and a Kowa hand-held applanation tonometer (HAT; Kowa Company, Ltd., Nagoya, Japan). Relationships between mean IOPs were evaluated using Pearson correlation coefficients, and the mean differences between tonometers, using one-way analysis of variance followed by Tukey-Kramer post-hoc analysis. Levels of agreement were evaluated using Bland-Altman analysis.
Results: The mean IOPs (mean ± SD) were 18.2 ± 3.5 mm Hg for iCare, 14.8 ± 3.4 mm Hg for Diaton, 16.7 ± 3.7 mm Hg for Tonopen XL, and 16.8 ± 2.8 mm Hg for Kowa HAT. Pearson correlation coefficients between iCare, Tonopen XL, and Kowa HAT ranged from 0.382 to 0.577, whereas those between Diaton and other tonometers ranged from 0.041 to 0.286. Post-hoc analysis indicated significant differences between all pairs except Tonopen XL and Kowa HAT. The mean difference between measurements from iCare and Diaton was 3.39 ± 3.39 mm Hg; iCare and Tonopen XL, 1.47 ± 3.52 mm Hg; iCare and Kowa HAT, 1.49 ± 2.90 mm Hg; Diaton and Tonopen XL, −1.93 ± 4.90 mm Hg; Diaton and Kowa HAT, −1.90 ± 4.15 mm Hg; and Tonopen XL and Kowa HAT, 0.02 ± 3.61 mm Hg. Computation of the width of the 95% limits of agreement resulted in a wide bias range when comparing Diaton with all tonometers. Relatively good agreements were observed between iCare, Tonopen XL, and HAT.
Conclusions: Intraocular pressure measurements obtained in a supine position by four portable tonometers were not interchangeable. Although iCare and Tonopen XL significantly overestimated IOP values in eyes with a higher IOP when compared with Kowa HAT, the agreements between iCare, Tonopen XL, and Kowa HAT were at clinically acceptable levels.