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   Table of Contents      
ORIGINAL ARTICLE
Year : 2006  |  Volume : 54  |  Issue : 4  |  Page : 261-265

Inter-instrument agreement and influence of central corneal thickness on measurements with Goldmann, pneumotonometer and noncontact tonometer in glaucomatous eyes


Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi - 110 029, India

Correspondence Address:
Viney Gupta
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi - 110 029
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0301-4738.27952

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  Abstract 

Purpose: This study was conducted to compare the intraocular pressure (IOP) measurements by the Goldman applanation tonometer (GAT), non contact tonometer (NCT) and the ocular blood flow (OBF) pneumotonometer in different IOP ranges in glaucomatous eyes. The effect of central corneal thickness (CCT) on IOP measurement in chronic glaucomatous eyes using the three different tonometers was also evaluated.
Materials and Methods: IOP measurements of 130 eyes of primary glaucoma patients were performed using GAT by an ophthalmologist while NCT and OBF-pneumotonometer measurements were performed by an experienced optometrist. The IOP values were compared amongst the three instruments in the three different IOP ranges (0-18 mmHg, >18 to 25 mmHg, > 25 mmHg). CCT was also measured in all patients.
Results: The mean of paired difference between GAT and NCT was 0.9 ± 3.1 mmHg while that between GAT and OBF-pneumotonometer was 0.3 ± 3.4 mmHg. The OBF-pneumotonometer and NCT were more affected by corneal thickness (0.41 mmHg and 0.4 mmHg / 10 µ corneal thickness respectively) while GAT was the least affected by corneal thickness (0.3 mmHg / 10 µ corneal thickness) though the difference was not statistically significant ( P =0.42).
Conclusion: With appropriate correction for corneal thickness the NCT and OBF-pneumotonometer can be used as reliably as GAT in following up glaucomatous patients.

Keywords: Central corneal thickness, glaucoma, goldmann applanation tonometer, non contact tonometer, ocular blood flow pneumotonometer


How to cite this article:
Gupta V, Sony P, Agarwal HC, Sihota R, Sharma A. Inter-instrument agreement and influence of central corneal thickness on measurements with Goldmann, pneumotonometer and noncontact tonometer in glaucomatous eyes. Indian J Ophthalmol 2006;54:261-5

How to cite this URL:
Gupta V, Sony P, Agarwal HC, Sihota R, Sharma A. Inter-instrument agreement and influence of central corneal thickness on measurements with Goldmann, pneumotonometer and noncontact tonometer in glaucomatous eyes. Indian J Ophthalmol [serial online] 2006 [cited 2020 Dec 5];54:261-5. Available from: https://www.ijo.in/text.asp?2006/54/4/261/27952

Table 2: Summary of previous studies in comparison to ours regarding IOP change for every 10 µ change in central corneal thickness using different tonometers

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Table 2: Summary of previous studies in comparison to ours regarding IOP change for every 10 µ change in central corneal thickness using different tonometers

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Table 1: The mean IOP differences between the 3 instruments in different IOP ranges

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Table 1: The mean IOP differences between the 3 instruments in different IOP ranges

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Intraocular pressure (IOP) measurement is important for diagnosis as well as for monitoring therapy in various glaucomas. Numerous factors influence the IOP measurement, especially central corneal thickness (CCT), corneal curvature and the technique used for the measurement. Goldmann applanation tonometer (GAT) is the most commonly used method for measurement of IOP. Various studies comparing the IOP measurements amongst GAT, non contact tonometer (NCT) and the ocular blood flow (OBF)-pneumotonometer are available in literature. These studies have shown a high correlation of IOP measurement amongst these three instruments within the normal IOP ranges. [1],[2],[3],[4],[5] Glaucoma patients have a wide range of IOPs and it may be of interest to know how these instruments compare with each other in different ranges of IOP and also to know the influence of CCT on IOP measurement by each of these instruments.

This study was conducted to compare the IOP measurement using GAT, NCT and OBF-pneumotonometer in different ranges of IOP in glaucomatous eyes and to evaluate the effect of CCT on IOP measurements by these techniques.


  Materials and Methods Top


Sixty-five primary glaucoma patients (30 primary open angle glaucoma, 22 primary chronic angle closure, 13 juvenile open angle glaucoma) with or without treatment were selected from the glaucoma services of our centre. The study was within the tenets of the Declaration of Helsinki. All patients underwent a detailed ophthalmic examination with optic disc evaluation and automated perimetry (Humphrey visual field analyzer, Model 745, Humphrey instruments; Full threshold program 30-2).

After taking an informed consent the IOP was measured in a random fashion (computer generated randomization) using GAT (Haag Streit, Berne, Switzerland), NCT (Nidek, NT 3000 Nidek Co. Ltd, Japan) and OBF-pneumotonometer (OBF Labs Ltd, Malmesbury, UK; now called the ocular blood flow analyzer, Paradigm Medical Industries, Inc, Salt Lake City, UT, USA). An interval of 15 min was maintained between two measurements. The measurements were recorded in different rooms so that the observer taking the GAT readings was masked to the results obtained from NCT and OBF. All the measurements with GAT were performed by a single experienced ophthalmologist while those with the NCT and OBF-pneumotonometer were performed by an experienced optometrist who was masked to the results of the GAT. All measurements were taken after calibration of the instrument. The eye was anesthetized using one drop of 0.5% paracaine. Goldmann applanation tonometry was performed in each eye three times and the mean IOP was recorded. A mean of three readings of NCT was used for analysis. Ocular blood flow pneumotonometry was performed with a slit-lamp mounted probe. The probe produced a whistling sound when applied in proper alignment over the central cornea. The mean IOP calculated automatically by the instrument was recorded.

The central corneal thickness (CCT) measurements were performed using the Orbscan corneal topography system (Orbtek Inc, Slat lake City, Utah).

This was done 1h after IOP measurements and an average of two readings was taken for analysis. If there was a problem in performing the CCT the same day, the patient was called again for CCT another day.

Statistical analysis was performed using SPSS software version 10.0. (SPSS for Windows, SPSS Inc. Chicago. IL). As a first step Pearson's correlation coefficient was used to find the correlation between the three methods of measurements. Then the mean IOP measurements by each of the instrument were compared. Mean differences between the methods called 'bias' and the 95% CI known as 'limits of agreement' between the instruments were calculated. An agreement between the tests was assessed using plots of differences against the means.[6] Influence of the change in corneal thickness on IOP measurement was also evaluated. A ' P ' value of <0.05 was considered significant.


  Results Top


The study comprised 130 eyes of 65 glaucoma patients. The mean age of the patients was 48 ± 10.2 years (range 26-71 years). The IOP range under study varied from 5 to 40 mmHg. Since both eyes were taken for analysis, correlation of IOP and CCT was done between the right and left eyes. No correlation was found for either IOP or CCT (r= 0.022, r= 0.22; P =0.68 and P =0.063 respectively). Analysis of covariance between the right and left eyes showed poor correlation of IOP (r= 0.058, P value =0.8) between eyes of the same patient whereas the variance for CCT was not significantly different (r=0.6, P value = 0.02) between the two eyes.

For analysis three groups were considered in the IOP ranges of 5-18 mmHg (n=48), >18-25 mmHg (n=53) and >25 mmHg (n=29). Mean CCT of the study group was 557 ± 54.6 µ.

There was a significant correlation between the NCT and OBF-pneumotonometer and GAT (r=0.88, P <0.001 and r=0.86, P <0.001 respectively) and also between the NCT and OBF-pneumotonometer (r=0.85, P <0.001). The mean of paired difference between GAT and NCT (GAT-NCT) was 0.9 ± 3.1 mmHg while that between GAT and OBF-pneumotonometer (GAT-OBF pneumotonometer) was 0.3 ± 3.4 mmHg, the differences being more at higher IOP ranges [Table - 1].

Agreement analysis showed that both OBF-pneumotonometer and NCT had a good agreement with GAT. The limits of agreement between GAT and OBF-pneumotonometer were 0.15 ± 2.46 and between GAT and NCT were 0.72±2.11. The 95% confidence limits of agreement were +5 mmHg and - 4.8 mmHg for GAT vs. OBF-pneumotonometer and + 4.9 mmHg and - 3.5 mmHg for GAT vs. NCT. These were within the clinically acceptable limits of agreement of + 3-5 mmHg.[7],[8] Out of 130 eyes, 78 (60%) measured with NCT were within ± 2 mmHg of GAT and 66 (51%) of those measured with Pneumotonometer were within ± 2 mmHg of GAT [Figure - 1].

Overall the three methods of IOP measurement showed a positive correlation with the CCT. The OBF-pneumotonometer and NCT were more influenced by CCT than GAT though the results were not significantly different ( P =0.42); for every 10 micron CCT change, the IOP change expected with GAT was 0.32, NCT was 0.4 and OBF was 0.41 as derived from a regression equation (Appendix 1) plot of CCT and IOP [Figure - 2]. When evaluated for different IOP ranges it was observed that IOP as measured by NCT showed a significant positive correlation with the CCT (r=0.491, P =0.002) in the IOP range of 0-18 mmHg compared to GAT and OBF-pneumotonometer (r=0.33, P =0.02 and r=0.45, P =0.08 respectively). All the three techniques showed a lesser significant positive correlation with the CCT in the range 19-25 mmHg (GAT r=0.266 P =0.036, OBF-pneumotonometer r=0.266, P =0.036, NCT r=0.267, P =0.036). In the higher IOP range of more than 25 mHg none of the three techniques significantly correlated with the CCT .


  Discussion Top


The technique of measurement and CCT are amongst the two most important factors that influence IOP measurement. In the course of follow-up of a glaucoma patient a number of observers and sometimes different instruments are involved in IOP measurement; it is thus important that the technique should have minimum variability between observers and the clinician must be aware of the agreement between different instruments. With both NCT and OBF-pneumotonometer being automatic the inter-observer variability is expected to be low while with many parameters involved in GAT measurements the inter-observer variability is expected to be high.[4],[9],[10]

Non contact tonometers are gaining popularity as they eliminate the potential risk of transmission of slow virus disease, do not require corneal anesthesia and are free from operator bias. In the present study GAT and NCT showed good agreement (limits of agreement 0.72±2.11 mmHg). We observed that the mean difference in the IOP readings between GAT and NCT was nearly equal in the midrange and higher range of IOP, with slight overestimation by NCT observed in the lower IOP range. Overall NCT underestimated the IOP by approximately 1.7 mmHg. Most studies with the NCT showed that it overestimates at low pressures and underestimates at high pressures when the IOP readings are compared with GAT.[3],[11],[12] This was also shown in our study. Tonnu et al. were the only authors to show using the Canon model of NCT that NCT underestimated IOP at lower ranges and overestimated it at higher IOP ranges.[13] Whereas previous studies have used the Keeler, Canon and Reichert AT 550 models[11],[12],[13],[14] we used the Nidek 3000. The OBF-pneumotonometer has the advantage of giving multiple IOP readings in a short span of 10 seconds and being able to calculate the pulse volume, pulse rate and thereby the pulsatile ocular blood flow. IOP recordings with GAT and OBF-pneumotonometer also exhibited a good agreement (limits of agreement 0.15±2.46 mmHg). Mean difference in the IOP readings between GAT and OBF-pneumotonometer was nearly equal in the midrange and lower range of IOP, the OBF-pneumotonometer overestimated the IOP slightly in lower IOP ranges, with underestimation by the OBF-pneumotonometer observed in the higher IOP range.

The agreement analysis was performed to see whether the NCT and the OBF-pneumotonometer agreed well with the GAT in different IOP ranges. The mean difference was low in the 0-18 mmHg IOP range but was higher at IOP ranges greater than 18 mmHg, especially between the GAT and NCT though within the clinically acceptable limits for agreement (± 5 mmHg).

CCT has been shown to be an important variable that can affect the IOP measurement.[5],[7],[15],[16],[17],[18],[19],[20],[21],[22] The effect of CCT varies with each technique of IOP measurement. As the CCT shows inter-individual variation, small variation in CCT has a small effect on IOP measurement, which may be clinically insignificant. However, larger variation in CCT may cause false estimation of the IOP resulting in misdiagnosis. Therefore for higher accuracy it is essential to know the quantitative effect of CCT on different IOP measuring techniques. Our study showed an overall correction factor of 0.35 mmHg on an average per 10 µ change in CCT. Previous clinical studies have shown a correction factor ranging from 0.18 to 0.63 mmHg per 10 µ change in CCT [Table - 2]. Ehlers et al .[20] showed a 0.7 mmHg change/10 µ change in CCT in canulated eyes where true IOP was measured by a manometer.

Among healthy individuals, the OBF-pneumotonometer and NCT have shown to be variably influenced by CCT as compared to GAT; while some authors have noted NCT to be minimally affected by CCT[2],[3],[22] others have shown as much as 3 mmHg IOP change with NCT for 10 microns change in CCT.[23] In a population-based study, Eysteinsson et al.[24] found 0.22-0.28 mmHg correction for 10 microns change in CCT using the NCT (Nidek 2000). This relationship of the IOP correction factor with CCT can also be different for different thicknesses of corneas. We observed that OBF-pneumotonometer and NCT showed a higher influence of CCT than GAT in glaucomatous eyes studied in our sample. This can be attributed to the fact the NCT applanates a wider area as compared to GAT.[3] While for GAT, a balance of applanating force on one side with IOP and corneal rigidity on the other side is considered as the end point of IOP measurement, for OBF-pneumotonometer the pressure of air flow has to exceed this balanced equilibrium, to escape. Therefore the corneal thickness has higher effect on OBF-pneumotonometer readings compared to those of GAT. In their study involving a large number of apparently healthy subjects Gunvant et al.[25] also noted that IOP measurements with OBF-pneumotonometer were more affected by CCT and in fact the instrument was twice as sensitive to CCT changes as compared to GAT.

The shortcoming of the study was the relatively small numbers of glaucoma patients studied. Also, using both eyes for analysis may have introduced the chance of getting a dependency bias. However, since many eyes had undergone previous surgery in one eye or were on medical therapy, there was a significant difference in the IOP between the eyes as was evident from the analysis of covariance. Hence such bias with regards to IOP was considerably reduced in this cross-sectional study. The effect of treatment on the hydration properties of the cornea was overlooked as this was not the aim of the present study.


  Conclusion Top


The results of the study suggest that IOP measurements using the NCT and OBF-pneumotonometer closely agree with those of GAT even in high IOP ranges. Intraocular pressure readings may require adjustment, especially when measured with NCT or OBF-pneumotonometer in those glaucomatous patients who have a CCT that is significantly different from population mean.



 
  References Top

1.
Esgin H, Alimgil ML, Erda S. Clinical comparison of the ocular blood flow tonograph and the Goldmann applanation tonometer. Eur J Ophthalmol 1998;8:162-6.  Back to cited text no. 1
[PUBMED]    
2.
Bhan A, Browning AC, Shah S, Hamilton R, Dave D, Dua HS. Effect of central corneal thickness on intraocular pressure measurements with the pneumotonometer, Goldmann applanation tonometer and Tono pen. Invest Ophthalmol Vis Sci 2002;43:1389-92.  Back to cited text no. 2
[PUBMED]  [FULLTEXT]  
3.
Masumoto T, Makino H, Uazoto H, Saishin M, Miyamoto S. The influence of corneal thickness and curvature on the difference between intraocular pressure measurements obtained with a non contact tonometer and those with a Goldmann applanation tonometer. Jpn J Ophthalmol 2000;44:691.  Back to cited text no. 3
    
4.
Sudesh S, Moseley MJ, Thompson JR. Accuracy of Goldmann tonometry in clinical practice. Acta Ophthalmol 1993;71:185-8.  Back to cited text no. 4
[PUBMED]    
5.
Singh RP, Goldberg I, Graham SL, Sharma A, Mohsin M. Central corneal thickness, tonometry and ocular dimensions in Glaucoma and Ocular hypertension. J Glaucoma 2001;10:206-10.  Back to cited text no. 5
[PUBMED]  [FULLTEXT]  
6.
Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1:307-10.  Back to cited text no. 6
[PUBMED]    
7.
Frenkel RE, Hong YJ, Shin DH. Comparison of the Tono-Pen to Goldmann applanation tonometer. Arch Ophthalmol 1988;106:750-3.  Back to cited text no. 7
[PUBMED]    
8.
Kao SF, Lichter PR, Bergstrom TJ, Rowe S, Musch DC. Clinical comparison of Oculab Tono-Pen to Goldmann applanation tonometer. Ophthalmology 1987;94:1541-4.  Back to cited text no. 8
[PUBMED]    
9.
Whitcare MM, Stein RA, Hassanein K. The effect of corneal thickness on applanation tonometry. Am J Ophthalmol 1993;115:592-6.  Back to cited text no. 9
    
10.
Dielemans I, Vingerling JR, Hofman A, Gobbee DE, de Jong PT. Reliability of intraocular pressure measurement with the Goldmann applanation tonometer in epidemiological studies. Grafes Arch Clin Exp Ophthalmol 1994;232:141-4.  Back to cited text no. 10
    
11.
Jorge J, Diaz-Rey JA, Gonzalez-Meijome JM, Almeida JB, Parafita MA. Clinical performance of the Reichert AT 550: A new non contact tonometer. Ophthalmic Physiol Opt 2002;22:560-4.  Back to cited text no. 11
[PUBMED]  [FULLTEXT]  
12.
Parker VA, Herrtage J, Sarkies NJ. Clinical comparison of Keeler Pulsair 3000 with Goldmann applanation tonometry. Br J Ophthalmol 2001;85:1301-4.  Back to cited text no. 12
[PUBMED]  [FULLTEXT]  
13.
Tonnu PA, Ho T, Sharma K, White E, Bunce C, Garway-Heath D. A comparison of four methods of tonometry: Method agreement and interobserver variability. Br J Ophthalmol 2005;89:847-50.  Back to cited text no. 13
[PUBMED]  [FULLTEXT]  
14.
Popovich KS, Shields MB. A comparison of intraocular pressure measurements with XPERT non Contact tonometer and Goldmann applanation tonometry. J Glaucoma 1997;6:44-6.  Back to cited text no. 14
[PUBMED]    
15.
Ko YC, Liu CL, Hsu WM. Varying effects of corneal thickness on intraocular pressure measurements with different tonometers. Eye 2005;19:327-32.  Back to cited text no. 15
    
16.
Wolfs RC, Klaver CC, Vingerling JR, Grobbee DE, Hofman A, de Jong PT. Distribution of central corneal thickness and its association with intraocular pressure. The Rotterdam eye Study. Am J Ophthalmol 1997;123:767-72.  Back to cited text no. 16
[PUBMED]    
17.
Graf M. Significance of corneal thickness in non-contact tonometry. Klin Monabu Augenheikd 1991;199:183-6.  Back to cited text no. 17
[PUBMED]    
18.
Tonnu PA, Ho T, Newson T, El Sheikh A, Sharma K, White E, et al . The influence of central corneal thickness and age on intraocular pressure measures by pneumotonometry, non contact tonometry, the Tono PenXL and Goldmann applanation tonometry. Br J Ophthalmol 2005;89:851-4.  Back to cited text no. 18
    
19.
Foster PJ, Basaanhu J, Alsbirk PH, Munkhbayar D, Uranchimeg D, Johnson GJ. Central corneal thickness and intraocular pressure in a Mongolian population. Ophthalmology 1998;105:969-73.  Back to cited text no. 19
    
20.
Ehlers N, Bramsen T, Sperling S. Applanation tonometry and central corneal thickness. Acta Ophthalmol 1975;53:34-43.  Back to cited text no. 20
    
21.
Brubaker RF. Tonometry and corneal thickness. Arch Ophthalmol 1999;117:104-5.  Back to cited text no. 21
[PUBMED]    
22.
Stabuc Silih M, Hawlina M. Influence of corneal thickness on comparative intraocular pressure measurements with Goldmann and non contact tonometers in keratoconus. Klin Monatsbl Augenheikd 2003;220:843-7.  Back to cited text no. 22
[PUBMED]  [FULLTEXT]  
23.
Cho P, Lam C. Factors affecting the central corneal thickness of Hong Kong-Chinese. Curr Eye Res 1999;18:368-74.  Back to cited text no. 23
[PUBMED]    
24.
Eysteinsson T, Jonasson F, Sasaki H, Arnarsson A, Sverrisson T, Sasaki K, et al . Central corneal thickness, radius of curvature and intraocular prssure in normal subjects using non contact techniques: Reykjavik eye study. Acta Ophthalmol Scand 2002;80:11-15.  Back to cited text no. 24
    
25.
Gunvant P, Baskaran M, Vijaya L, Joseph IS, Watkins RJ, Nallapothula M, et al . Effect of corneal parameters on measurements using the pulsatile ocular blood flow tonograph and Goldmann applanation tonometer. Br J Ophthalmol 2004;88:518-22.  Back to cited text no. 25
    


    Figures

  [Figure - 1], [Figure - 2]
 
 
    Tables

  [Table - 1], [Table - 2]


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