J Korean Ophthalmol Soc.  2015 Mar;56(3):404-412. 10.3341/jkos.2015.56.3.404.

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

• Han JW
• Ha SJ

• KMID: 2339047
• DOI: http://doi.org/10.3341/jkos.2015.56.3.404

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.

Keyword

Corneal biomechanics values; Corvis scheimpflug technology tonometer; Glaucoma; Intraocular pressure

MeSH Terms

Corneal Pachymetry
Elasticity
Glaucoma
Glaucoma, Open-Angle
Humans
Intraocular Pressure
Low Tension Glaucoma
Viscosity

Figure

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  Figure 1. Intraocular pressure measurement by CST. A high speed Scheimpflug camera was equipped to record the movement of cornea. The output also includes central corneal thickness and corneal biomechanical properties (applanation time, applanation length, applanation velocity, and parameters of highest concavity). CST = Corvis scheimpflug technology; IOP = intraocular pressure.

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  Figure 2. Analysis of variance between mean intraocular pressure values measured by different tonometers. There was no statistically significant difference in IOP measurement among the tonometers by ANOVA (CST vs GAT, p = 0.265 CST vs NCT, p = 0.057 CST vs RBT, p = 0.744). IOP = intraocular pressure; CST = Corvis scheimpflug technology; GAT = Goldmann applanation tonometer; NCT = noncontact tonometer; RBT = rebound tonometer.

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  Figure 3. Bland-Altman plots between different tonometers. The solid line indicates mean difference of both tonometers. The dotted lines are 95% of limits of agreement. CST = Corvis scheimpflug technology; GAT = Goldmann applanation tonometer; NCT = noncontact tonometer; RBT = rebound tonometer.

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  Figure 4. Correlation of CST, GAT, NCT and RBT. Significant positive correlations were noted between CST and GAT (R = 0.670, p < 0.001), between CST and NCT (R = 0.746, p < 0.001) and between CST and RBT (R = 0.679, p < 0.001) by Spearman correlation. CST = Corvis scheimpflug technology; GAT = Goldmann applanation tonometer; NCT = noncontact tonometer; RBT = rebound tonometer.

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  Figure 5. Bland-Altman plots between US-CCT and Corvis-CCT. The solid line indicates mean difference of both tonometers. The dotted lines are 95% of limits of agreement. US = ultrasound; CCT = central corneal thickness.

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