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Table of Contents
Year : 2021  |  Volume : 3  |  Issue : 1  |  Page : 3

Concordance between Goldmann, Icare Pro®, Corvis ST® and Tonopen® tonometry, and their correlation with corneal thickness

Department of Ophthalmology, Hospital Militar Central, Universidad Militar Nueva Granada, Bogotá, Colombia

Date of Submission25-Aug-2020
Date of Acceptance23-Oct-2020
Date of Web Publication13-Jan-2021

Correspondence Address:
Dr. Patricia Hernandez Mendieta
Calle 138 # 74 . 51 Casa 27, Bogota
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/PAJO.PAJO_44_20

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Introduction: The objective is to evaluate the concordance of intraocular pressure (IOP) values by comparing three tonometers; Corvis ST (COR), Icare Pro (ICA) and Tonopen (TOP) with the gold standard, the Goldmann applanation tonometry (GAT and the effect of the measurements by the central corneal thickness (CCT).
Methods: One hundred and eight eyes were selected (59 patients) who underwent IOP measurement with four instruments (Icare, Corvis, Tonopen and Goldmann). An univariate analysis was applied, and then a concordance analysis was performed in which the intraclass correlation coefficient (ICC) was calculated between the different instruments taking into account the corneal thicknesses to eliminate confounding effect in measurements.
Results: 109 eyes (59 patients) were included, 66% women and 34% men. Average age 52.2 years (SD 13.87). Univariate analysis was performed and a mean age 52.2 (SD ± 13.87) and mean IOP were obtained for Goldman 15 (SD ± 2.94), Icare 15 (SD ± 2.47), Tonopen 14 ( SD ± 2.85), Corvis 14 (SD ± 2.67).

Keywords: Corvis ST, glaucoma, Goldmann, Icare Pro, intraocular pressure, tonometer, tonometry, tonopen

How to cite this article:
Mendieta PH, Puerto ML, Goyeneche FG, Guacaneme AC. Concordance between Goldmann, Icare Pro®, Corvis ST® and Tonopen® tonometry, and their correlation with corneal thickness. Pan Am J Ophthalmol 2021;3:3

How to cite this URL:
Mendieta PH, Puerto ML, Goyeneche FG, Guacaneme AC. Concordance between Goldmann, Icare Pro®, Corvis ST® and Tonopen® tonometry, and their correlation with corneal thickness. Pan Am J Ophthalmol [serial online] 2021 [cited 2021 Nov 27];3:3. Available from: https://www.thepajo.org/text.asp?2021/3/1/3/306947

  Introduction Top

Glaucoma is the most common cause of irreversible blindness in the world, associated with increased intraocular pressure (IOP), without being an obligatory condition.[1],[2] It is a prevalent disease in all races; however, there is a special predisposition in some racial groups, such as black people[3] and the Latin American population; This is due to the fact that in these breeds a greater amount of pigment is deposited in the trabecular meshwork that does not allow the normal flow of aqueous humor and consequently raises IOP.[4],[5] Screening for the early stages of glaucoma could be based on the evaluation of patients with ocular hypertension,[6] bearing in mind that IOP reduction is the mainstay of treatment, and several studies have shown effectiveness in reducing the rate in the progression of the disease.[7],[8] The Goldmann applanation tonometry (GAT) was introduced since 1957, and it is considered the gold standard that estimates the IOP as the force required to flatten the cornea, derived from the Imbert-Fick principle.[9],[10] However; there are multiple factors that can distort the Goldmann tonometry results, such as corneal thickness, corneal curvature, and patient accommodation, as well as being a test with a certain subjective component.[11],[12]

The Tonopen (TOP) was introduced in the 80s, it is a portable device with a replaceable latex head, easy to use. It estimates the average of 10 measurements and is especially useful in irregular corneas or with edema, even in contact lens wearers.[13] The Icare (ICA) is a rebound tonometer, used since 1997.[14] The measurement procedure consists of contacting the probe by touching the central cornea, analyzing by means of a microprocessor the deceleration of the probe after the impact, in this way the IOP is taken after averaging six measurements.[15],[16] The Corvis ST (COR) provides an IOP value corrected for the corneal biomechanical parameters and incorporates a Scheimpflug camera (Optikgeräte GmbH, Wetzlar, Germany) that allows a real-time image of the anterior chamber of the eye where the corneal deformability in resulting to air impulse is shown.[17] The corneal biomechanical parameters it provides are the speed, time, and length of the first and second applanation, maximum concavity, amplitude of deformation, and corneal radius.[18],[19] As IOP is the only modifiable risk factor in the progression of glaucomatous optic neuropathy,[20] it is important to identify different measurement devices, know their principles, and correlate the differences in IOP measurements that can be obtained with each one of them.[21],[22] The objective of this article is to evaluate the concordance of the different methods for taking IOP and to identify the differences that can be generated due to central corneal thickness.

  Materials and Methods Top

Prospective analytical study of diagnostic test and concordance: 108 eyes were selected from 59 patients attending ophthalmological consultation at the “Country” medical unit. The sample selection was non-probabilistic for convenience in patients who attended the consultation. The inclusion criteria were: Age between 18 and 80 years, complete ophthalmological evaluation, and no gender distinction.

Patients with filtering surgery, tear film alteration, corneal pathology, refractive surgery in the last 3 months, and a history of keratoplasty were excluded. The main outcome was the concordance between IOP measurements with the different devices available for taking. Three (3) measurements were taken with each tonometer, with intervals of at least 3 min between measurements and 5 min between tonometers. All measurements were made by the same observer who did not know the objective of the investigation.

The devices used and the method of measurement were the following: Goldmann tonometry (GAT, Haag-Streit, Koeniz, Switzerland) with which IOP was taken with fluorescein and previous instillation of a topical anesthetic (Proxymetacaine) 5 min after the first measurement, IOP was taken with the Icare PRO (ICare®, Tiolat Oy, Helsinki, Finland), Tono-Pen AVIA® Tonometer and Corvis ST tonometers (Optikgeräte GmbH, Wetzlar, Germany), with 5 min intervals between instruments.

Three valid measurements were made with Goldmann, Corvis, Icare, and Tonopen using the average value of each tonometer for the statistical analysis.

Statistical analysis was performed using the SPSS version 22.0 software for Windows (SPSS Inc., Chicago, IL, USA) and Excel. A univariate analysis was performed to determine the absolute and relative frequencies for the sociodemographic characteristics. Subsequently, an analysis of concordance with intraclass correlation coefficient (ICC) was performed between the IOPs taken by the different tonometers; these results were stratified according to the pachymetry values previously recorded in medical history. It was stratified into thin corneas <521 microns, normal corneas 521–550μ, and thick corneas >551μ to eliminate the potential modifying effect of corneal thickness on IOP measurements.

The study protocol was evaluated by the ethics committee of the Central Military Hospital of Bogotá which abides by the declaration of Helsinki, adopted in 2013, as well as Resolution number 8430 of the Ministry of Health of Colombia. During the investigation, the respective informed consents for the intervention were signed, and the confidentiality of the information related to the patients was guaranteed.

  Results Top

108 eyes of 59 healthy subjects who met the inclusion criteria were studied. The mean age was 58 (24–88) years. The distribution by sex was 66.3% women and 36.7% men [Table 1].
Table 1: Sociodemographic data

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The mean corneal thickness was 534 μm (462–752 μm). Mean IOP measurement values for the Goldmann tonometer were 15.08 mmHg (standard deviation [SD] ± 2.94); with Icare tonometry were 14.61 mmHg (SD ± 2.47); the Tonopen were 14.15 mmHg (SD ± 2.85); and Corvis ST were 14.27 mmHg (SD ± 2.67) [Table 2].
Table 2: Average intraocular pressure (standard deviation)

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For concordance evaluation, it was considered that the ICC is low if it is <0.4, moderate between 0.4 and 0.75 and excellent if it is above 0.75. Concordance analyzes were stratified according to corneal thickness, the results showed that among all the measurement methods the concordance was moderate with an average ICC of 0.58. For the tonometry with Icare versus Goldmann, the agreement was moderate for all corneal thicknesses (ICC 0.66, 0.516, and 0.63). The Tonopen versus Goldmann tonometers showed moderate agreement for thin and thick corneas (ICC 0.53 and 0.64) and low for normal corneas (ICC 0.36); Regarding the Corvis versus Goldmann concordance for thin and thick corneas, the results were moderate (ICC 0.498 and 0.496), and in normal corneas, they were poor (ICC 0.183) [Table 3].
Table 3: Concordance analysis

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  Discussion Top

The measurement of IOP by the different Icare, corvis ST, and Tonopen tonometers displays a moderate agreement when compared to Goldmann tonometry in patients with thin corneas. For patients with normal corneas, the agreement is moderate only with Icare; with the rest of tonometers the agreement was lower. Regarding thick corneas, all the tonometers showed moderate agreement. The results of this article show that the tonometer with the highest agreement between the IOP measurements compared to the gold standard was the Icare, followed by Tonopen and finally Corvis ST, which showed a moderate and lower ICC. These results are consistent with other studies. For instance, Chen et al. conducted a study in which they compared noncontact tonometers versus Icare versus Goldmann and found a high concordance between Icare and Goldmann;[17] corneal thickness was also found to mainly affect noncontact tonometers and to a lesser extent, Icare and Goldmann.[23],[24] On the other hand, studies have been found that conclude that there is no involvement of corneal thickness when taking IOP with other tonometers. Ramm et al. in their study reported that there was no influence of corneal thickness on IOP values during taking with Corvis ST, but there is a negative correlation between Goldmann tonometry and corneal thickness.[19] However, multiple studies have been carried out that show sources of error in taking IOP regardless of the type of tonometer and that I suggest the use of continuous measurements even in home intakes, which have shown no differences with the tonometry performed in the office.[25],[26],[27],[28]

This study concludes that the most concordant method for taking the IOP is IcarePro (ICA) compared to the gold standard; similarly, it is evident that the thickness of the cornea exerts a more pronounced modifying effect in some tonometers. It is important to expand the evidence on how tonometry can be performed. In Colombia, there are few studies that allow to evaluate IOP taking methods; therefore, it is necessary to study the variability that can be had in the population due to the versatility of factors such as race, gender and age, among others;[29],[30] in order to provide the best diagnostic method that allows early detection of IOP elevation as the main risk factor for glaucoma.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Table 1], [Table 2], [Table 3]


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