Evaluation of Corvis ST tonometer with the updated software in glaucoma practice

Abstract

AIM: To evaluate the agreement of biomechanically corrected intraocular pressure (b-IOP) and central corneal thickness (CCT) measurements obtained with the updated Corvis ST tonometer versus Goldmann applanation tonometry (GAT) and optical-based corneal pachymetry (OB-CCT) in controls, patients with ocular hypertension (OHT) and primary open angle glaucoma (POAG). Additionally, we examined the differences in corneal deformation parameters provided by the updated Corvis ST among the three groups. METHODS: For each participant, GAT IOP, OB-CCT and measurements with a Corvis ST with updated software were obtained. Bland-Altman analysis was used to assess the agreement between the two measurement methods. RESULTS: A consecutive series of 80 eyes from 80 participants (30 with POAG, 25 with OHT and 25 normal controls) were included in this prospective study. The mean GAT IOP of all eyes was 17.2±3.6 mm Hg, and the mean b-IOP was 15.9±3.7 mm Hg (Spearman's rho=0.767, P<0.001). The 95% limits of agreement (LoAs) ranged from -3.1 mm Hg to 5.5 mm Hg for GAT IOP and b-IOP. b-IOP was not correlated with OB-CCT (Spearman's rho=-0.13 P=0.917). Meanwhile there was a weak positive corelation between OB-CCT and GAT IOP–b-IOP difference (Spearman's rho=0.378, P=0.001). The mean OB-CCT was 549.5±36.4 µm, and the Corvis-CCT was 556.1±41.5 µm (Spearman's rho=0.900, P<0.001). No statistically significant difference in the new indices provided by the updated Corvis ST was detected among the three groups. Compared with control eyes, POAG eyes had a significantly reduced applanation time 2 after adjusting for OB-CCT and GAT IOP (P=0.048). CONCLUSION: Corvis b-IOP and CCT correlate well with GAT IOP and OB-CCT. b-IOP is not affected by CCT, which might be an advantage, especially in thick or thin corneas. Corvis ST yields shorter applanation time 2 measurements in patients with POAG, which might reflect altered corneal viscoelasticity.