Journal List > J Korean Ophthalmol Soc > v.53(7) > 1009408

Lee, Seong, Kang, Cho, and Lee: Comparison of Rebound Tonometer, Non-Contact Tonometer, Goldmann Applanation Tonometer and the Relationship to Central Corneal Thickness

Abstract

Purpose

To compare the level of accuracy of intraocular pressure (IOP) measurements of a rebound tonometer (RT) Icare®, and non-contact tonometer (NCT), using Goldmann Applanation tonometer (GAT) as a reference to evaluate the influence of central corneal thickness (CCT) on IOP readings in the Korean population.

Methods

In a prospective study of 273 eyes, IOP was measured with RT, GAT, and NCT and compared to CCT measurements. Patients were assigned to one of 3 groups based on IOP measurements of GAT and 1 of 2 groups based on CCT. The comparison of the IOP values of RT, GAT, and NCT was performed between the IOP and CCT groups, and the differences among tonometers were evaluated.

Results

The RT showed statistically significant correlation with the GAT compared to the NCT. The CCT was related to RT measurements. The RT values compared to the GAT was underestimated in thin corneas and overestimated in thick corneas.

Conclusions

There was a significant correlation between the RT and the GAT measurements compared with the NCT. However, RT is influenced by CCT and correlates less with GAT in low IOP ranges, suggesting that corneal thickness should be taken into consideration during such measurements.

Figures and Tables

Figure 1
The correlation between Goldmann applanation tonometer and rebound tonometer IOP measurements (r = 0.913, p < 0.001).
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Figure 2
Bland-Altman plots of agreement between Goldmann applanation tonometer and rebound tonometer for each eye measured (A), and Goldmann applanation tonometer and Non-contact tonometer (B). The differences in IOP of both tonometers (Goldmann applanation tonometer value minus rebound tonometer value (or non-contact tonometer value), mmHg) is plotted against the average of the IOP of both tonometers. The solid line is the mean of the average IOP values of both tonometers. The dotted horizontal lines are ±1.96 SD confidence interval (CI) (i.e. 95% of the points should fall within these lines).
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Figure 3
Frequency distribution of differences between rebound tonometer, Goldmann applanation tonometer, and noncontact tonometer measurements.
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Figure 4
Scatterplots showing the relationship between central corneal thickness and IOP value of Goldmann applanation tonometer (R2 = 0.057, p < 0.001) (A), IOP values of rebound tonometer (R2 = 0.104, p < 0.001) (B).
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Table 1
Summary of the subject characteristics, IOP measurements (mm Hg) using the 3 tonometers, and corneal thickness
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Data are expressed as mean ± SD or number.

IOP = intraocular pressure; IOPNCT = IOP measurement of a noncontact tonometer; IOPRT = IOP measurement of a Icare rebound tonometer; IOPGAT = IOP measurement of a Goldmann applanation tonometer; CCT = central corneal thickness.

Table 2
Bland-Altman analysis of IOP measurements using different tonometers (mean difference ± SD and 95% LoAs)
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IOP = intraocular pressure; IOPNCT = IOP measurement of a noncontact tonometer; IOPRT = IOP measurement of a Icare rebound tonometer; IOPGAT = IOP measurement of a Goldmann applanation tonometer; CCT = central corneal thickness; SD = standard deviation; LoA = limits of agreement; Lower LoA = mean - 1.96 × SD; Upper LoA = mean + 1.96 × SD; Width of LoA = upper LoA-lower LoA.

Table 3
Comparison of the IOP measurements of Icare® rebound tonometer, Goldmann applanation tonometer, and noncontact tonometer and the mean differences of each tonometers between low IOP, medium IOP, and high IOP by GAT
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IOP = intraocular pressure; GAT = Goldmann applanation tonometer; IOPNCT = IOP measurement of a noncontact tonometer; IOPRT = IOP measurement of a Icare rebound tonometer; IOPGAT = IOP measurement of a Goldmann applanation tonometer; CCT = central corneal thickness.

*Mean difference of IOPs measured by two tonometers; Correlation of IOP by Goldmann applanation tonometer and IOP by rebound tonometer (pearson correlation analysis).

Table 4
Comparison of the IOP measurements of Icare® rebound tonometer, Goldmann applanation tonometer, and noncontact tonometer and the mean differences of each tonometers between thinner CCT group and thicker CCT group
jkos-53-988-i004

Values are presented as mean ± SD.

IOP = intraocular pressure; GAT = goldmann applanation tonometer; NCT = noncontact tonometer; CCT = central corneal thickness; IOPGAT = IOP measurement of a Goldmann applanation tonometer; IOPRT = IOP measurement of a Icare rebound tonometer; IOPNCT = IOP measurement of a noncontact tonometer.

*Statistical significance was tested by independent paired t-test; Correlation between the IOP measurements of two tonometers by pearson correlation analysis.

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