The Accuracy of Corvis ST for the Measurement of Intraocular Pressure and Central Corneal Thickness in Glaucoma

Objective: To evaluate the accuracy of intraocular pressure (IOP) and central corneal thickness (CCT) measured by corneal visualization scheimpflug technology (CST), and to investigate the influence of corneal biomechanical properties on IOP. Methods: For this descriptive study, 28 glaucoma patients (56 eyes) were recruited. An experienced clinician obtained IOP measurements with both the CST and the Goldmann applanation tonometer (GAT). CCT measurements were obtained with the CST and the IOLMaster. The results of the different devices were compared by paired t-tests. The correlation between IOP measurements by the CST and the GAT and between the CCT measurements by the CST and the IOLMaster were assessed by a nonparametric Spearman test. Device agreement was calculated by Bland-Altman analysis. Results: The mean IOP measured by the CST, 19.5±12.0 mmHg, was not significantly different for that measured by the GAT, 20.9±8.8 mmHg. The mean CCT was 544±40 μm for CST and 538±40 μm for the IOLMaster. Both pairs of devices showed a high correlation for the respective measurements (ρ=0.837, 0.958, both P<0.001). Bland-Altman analysis revealed an IOP bias between the CST and the GAT of 1.3±5.4 mmHg with 95% limits of agreement of -9.3 to 12.0 mmHg. There was also a CCT bias between the CST and the IOLMaster of 6±10 μm, with 95% limits of agreement of -26 to 15 μm. Conclusions: The CST precision is excellent for IOP and CCT measurements. CST can result in a lower IOP measurement than GAT, so these devices may not be interchangeable in the diagnosis and treatment of glaucoma. Key words: Corvis ST; corneal biomechanical properties; intraocular pressure; central corneal thickness; glaucoma