Comparison of Corvis ST Tonometer to Other Tonometers and Clinical Usefulness of Corvis ST Tonometer

ABSTRACT

PURPOSE: To compare the accuracy and agreement of intraocular pressure (IOP) and central corneal thickness (CCT) measurements with noncontact tonometer Corvis Scheimpflug Technology (Corvis ST) versus noncontact tonometer (NCT), Goldmann applanation tonometer (GAT), rebound tonometer (RBT), and ultrasound-based corneal pachymetry (US-CCT). The secondary objective was to evaluate the corneal biomechanical values using Corvis ST tonometer in patients with glaucoma. METHODS: Thirty-one healthy participants and 47 patients with primary open angle glaucoma and normal tension glaucoma were enrolled in this study. One eye was selected randomly. In each participant, GAT, NCT, RBT, US-CCT and measurements with Corvis ST (Corvis-IOP and Corvis-CCT) were obtained. IOP and CCT measurements of each device were compared. Device agreement was calculated by Bland-Altman analysis. Additionally, corneal highest concavity parameters were compared between healthy subjects and glaucoma patients. RESULTS: Mean IOPs in all examined eyes were 13.28 +/- 2.32 mm Hg for CST, 14.71 +/- 2.95 mm Hg for GAT, 14.44 +/- 3.10 mm Hg for NCT, and 13.23 +/- 2.89 mm Hg for RBT. There was no statistical difference in IOP measurements among tonometers. Correlation analysis showed a high correlation between each pair of tonometers (all p < 0.0001). Bland-Altman plots of all devices revealed good agreement of the IOP and CCT measurements. In glaucoma patients, highest concavity time and peak distance of highest concavity parameters were statistically lower than in normal subjects (16.93 +/- 0.66 ms vs. 16.48 +/- 0.84 ms p = 0.020, 4.23 +/- 1.34 mm vs. 3.41 +/- 1.27 mm p = 0.017, respectively). CONCLUSIONS: The CST, a newly-developed tonometer with features of visualization and measurement of the corneal deformation response to an air impulse, can be considered a reliable alternative method for measuring IOP and CCT in healthy subjects and glaucoma patients. Highest concavity parameters could be another important indicator identifying corneal viscosity or elasticity in patients with glaucoma.