A new Tonometer-the Corvis ST Tonometer Clinical Comparison with Non-contact, and Goldmann Applanation Tonometers

Abstract

 

Purpose

 

To compare intraocular pressure (IOP) measurements obtained using Topocon non-contact tonometer (NCT), Goldmann applanation tonometer (GAT), and Corvis ST (CST), a newly developed tonometer with features of visualization and measurement of the corneal deformation response to an air pulse. A secondary objective was to assess the agreement among the devices.

 

Methods

 

Fifty-nine participants with a mixture of glaucoma patients (36 cases with 36 eyes) and control volunteers (23 cases with 23 eyes) were enrolled. The IOP measurements were obtained with the CST, NCT, and GAT by two experienced clinicians. IOP values were compared. Repeatability and reproducibility were assessed by the coefficient of variation and intraclass correlation coefficient. Device agreement was calculated by Bland-Altman analysis.

 

Results

 

Mean IOP for all examined eyes was 18.9 ± 5.8 mmHg for CST, 21.3 ± 6.8 mmHg for NCT, and 20.3 ± 5.7 mmHg for GAT. There was a statistically significant difference in IOP measured among different tonometers. However, correlation analysis showed a high correlation between each pair of these three devices (All P<0.001). The CST displays the best repeatability and reproducibility. Bland-Altman analysis revealed a bias between CST and GAT, CST and NCT, and GAT and NCT of -1.3, -2.4, and -1.1 mmHg, with 95% limits of agreement of -6.2 to 3.5 mmHg, -10.1 to 5.2 mmHg, and -8.3 to 6.2 mmHg, respectively.

 

Conclusions

 

Although the CST may significantly underestimate IOP in relation to GAT and NCT, it offers an alternative method for measuring IOP. The IOP measurements taken with each device may not be interchangeable.

 

 

Figure 1. Intraocular pressure measurement by Corvis ST (CST). (A) Real-time information of a participant recorded immediately upon an air impulse. (B) Real-time information of a participant recorded at the highest concavity, indicating the biggest deformation amplitude of the cornea.

 

 

Figure 2. Correlation among different IOP measurement devices. Significant positive correlations were noted (A) between CST and NCT (ρ =0.871; P<0.001), (B) between CST and GAT (ρ =0.896; P<0.001), (C) and between GAT and NCT (ρ =0.839; P<0.001). Bland-Altman scatterplot showing the agreement among different IOP measurement devices: (D) between a Corvis ST tonometer (CST) and a Goldmann applanation tonometer (GAT). (E) between CST and Non-contact tonometer (NCT). (F) between GAT and NCT.

 

Keywords: 568 intraocular pressure • 479 cornea: clinical science • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)