Journal of Ophthalmology

Journal of Ophthalmology / 2014 / Article

Clinical Study | Open Access

Volume 2014 |Article ID 461681 | https://doi.org/10.1155/2014/461681

Yuta Sakaue, Jun Ueda, Masaaki Seki, Takayuki Tanaka, Tetsuya Togano, Takaiko Yoshino, Takeo Fukuchi, "Evaluation of the New Digital Goldmann Applanation Tonometer for Measuring Intraocular Pressure", Journal of Ophthalmology, vol. 2014, Article ID 461681, 5 pages, 2014. https://doi.org/10.1155/2014/461681

Evaluation of the New Digital Goldmann Applanation Tonometer for Measuring Intraocular Pressure

Academic Editor: Christoph Tappeiner
Received06 Apr 2014
Accepted30 Jun 2014
Published10 Jul 2014

Abstract

Purpose. To compare a new digital Goldmann applanation tonometer (dGAT) that measures intraocular pressure (IOP) in 0.1 mmHg increments to a standard Goldmann applanation tonometer (sGAT). Methods. This study included 116 eyes of 60 subjects. A single examiner first measured IOP in triplicate using either sGAT or dGAT, which was randomly chosen. After a 5-minute interval, the next set of three consecutive IOP was measured using the other GAT. Results. The mean IOP measured with sGAT was 16.27 ± 6.68 mmHg and 16.35 ± 6.69 mmHg with dGAT. Pearson’s correlation coefficient was 0.998 (). The subjects were divided into three groups based on the mean IOP: IOP < 14 mmHg, 14–20 mmHg, or >20 mmHg. The Pearson’s correlation coefficient within each group was 0.935, 0.972, and 0.997 (), respectively. The difference within the three consecutive IOP measurements (maximum–minimum) for dGAT (0.72 ± 0.34 mmHg) was significantly smaller than those with sGAT (0.92 ± 0.42 mmHg, ). Even in patients with equal IOP (zero left-right difference) with sGAT (), dGAT detected IOP differences between the left and right eyes (0.47 ± 0.31 mmHg). Conclusion. Compared to sGAT, dGAT measurements are highly reproducible and less variable.

1. Introduction

The pathogenesis and long-term natural history of glaucomatous optic neuropathy is still under active investigation. Many clinical trials have confirmed the key role intraocular pressure (IOP) plays in the development and progression of open-angle glaucoma [114]. Such studies have shown that lowering IOP reduces the risk of developing open-angle glaucoma and slows its progression. According to the Ocular Hypertension Treatment Study (OHTS) [1, 2], the risk of developing glaucoma is reduced from 9.5% to 4.4% when a mean IOP reduction of 22.5% was achieved with topical medications. Treatments that reduce IOP also reduced the proportion of patients with progression of clinically apparent glaucoma from 62% to 45% in the Early Manifest Glaucoma Trial (EMGT) [36], and from 27% to 12% in the Collaborative Normal-Tension Glaucoma Study (CNTGS) [79].

The current treatment strategy for glaucoma is to lower IOP in order to suppress the progression of glaucomatous optic neuropathy. Tonometry is one of the most important examinations in glaucoma management. With more accurate tonometry, more precise evaluation of reductions in IOP or the effects of glaucoma management may be possible.

The Goldmann applanation tonometer (GAT) is one of the most commonly accepted instruments to measure IOP. Despite the benefits of noncontact tonometers, they have a larger coefficient of variation than that of GAT and can result in larger measurement errors in patients with IOP < 10 mmHg or >25 mmHg [15]. The Tono-Pen (Medtronic Solan, Jacksonville, FL, USA) is more likely to have higher variability than GAT and produces lower readings in patients with ocular tension ≥20 mmHg [16]. GAT is widely adopted as the gold standard in tonometry due to its accuracy and excellent reproducibility. However, the standard Goldmann applanation tonometer (sGAT) has 2 mmHg markings on the drum, which can lead to disadvantages such as variability due to reading or digit preference [17, 18].

AT900D (Haag-Streit International, Koeniz, Switzerland) is a new digital Goldmann applanation tonometer (dGAT). The principles and basic methods for IOP measurement are the same as those of sGAT; however, the measurements are shown to the 0.1 mmHg level on the display (Figure 1).

In this study, measurements obtained with sGAT and dGAT were compared to assess the accuracy and possible advantages of dGAT.

2. Materials and Methods

This study included 116 eyes of 60 subjects, including 15 eyes of 8 healthy subjects and 101 eyes of 52 patients with glaucoma. Table 1 shows the profiles of the participants. Patients with a history of surgery for glaucoma and corneal disease were excluded. The study protocol was designed according to the norms of the Declaration of Helsinki. Written informed consent was obtained from the participants.


Sex
 Male 61 eyes of 32 patients
 Female 55 eyes of 28 patients
Age (mean ± SD) years
Diagnosiseyes
 Primary open-angle glaucoma 38
 Normal-tension glaucoma37
 Developmental glaucoma8
 Exfoliation glaucoma5
 Chronic angle-closure glaucoma 6
 Uveitis and secondary glaucoma7
 Healthy 15

The sGAT employed in this study was the AT900 (Haag-Streit International). Although the instrument has 2 mmHg markings on the drum (Figure 1), measurements were made to the 1 mmHg level. The dGAT employed in this study was the AT900D. Digital measurements were obtained to the 0.1 mmHg level (Figure 1). For IOP measurement, the eye was anesthetized with 0.4% oxybuprocaine. Fluorescein was applied to the inferior fornix using a standard fluorescein paper strip. A single examiner (Y.S.) first measured IOP in triplicate for each eye using either sGAT or dGAT, which was randomly chosen. After a 5-minute interval, the next set of three consecutive IOP measurements was obtained with the other GAT. The three IOP readings were averaged to obtain IOP for the eye.

The mean IOP in the right eye of the 60 patients as determined by sGAT and dGAT were compared using Pearson’s correlation analysis. A Bland-Altman plot was constructed to evaluate agreement and calculate confidence intervals (CIs). For each eye, differences in IOP measurements (maximum–minimum) based on sGAT and dGAT were compared to study the dispersion in measurements using Student’s -test. A value <0.05 was considered to indicate statistical significance. The second of the three sGAT and dGAT readings for each eye was used to evaluate differences between IOP in the left and right eye. The left-right difference in IOP measured by dGAT was calculated in patients with equal left and right sGAT measurements.

3. Results

The mean IOP of the 60 eyes measured using sGAT was  mmHg and that for dGAT was  mmHg. Pearson’s correlation analysis revealed a significant positive correlation between sGAT and dGAT measurements of IOP (Table 2 and Figure 2: , ). When the subjects were divided into three groups based on the mean sGAT IOP value (≤14 mmHg, 30 eyes; 14–20 mmHg, 21 eyes; or ≥20 mmHg, 9 eyes), sGAT and dGAT measurements within each stratum showed strong positive correlation (Table 2: , ; , ; and , ; resp.). According to Bland-Altman analysis, dGAT measurements showed no skew compared to sGAT measurements (Figure 3, ). The mean difference (sGAT-dGAT) in IOP readings for each eye was  mmHg (). The difference (maximum–minimum) within each set of three dGAT measurements was  mmHg, which was significantly smaller than that for sGAT ( mmHg, , ).


All eyesGroup 1Group 2 Group 3
(IOP ≤ 14)(14 < IOP < 20)(IOP ≥ 20)

Number of patients6030219
Standard GAT (mmHg)
Digital GAT (mmHg)
Pearson’s correlation coefficient0.9980.9350.9720.997
value<0.01<0.01<0.01<0.01

IOP: intraocular pressure; GAT: Goldmann applanation tonometer.
Pearson’s correlation coefficient test.

The second reading in each set of sGAT or dGAT measurements was used to analyze differences between left and right eyes, because it was closest to the mean of the three tonometry measurements. Of 60 patients examined, 30 patients had equal IOP in both eyes based on sGAT (i.e., zero left-right difference). The mean left-right difference detected by dGAT in these 30 patients with no left-right difference on sGAT was  mmHg (range: 0-1.0 mmHg).

4. Discussion

New tonometers such as the rebound tonometer and dynamic contour tonometer have been developed recently. The rebound tonometer is portable and does not require topical anesthesia. However, it is likely to show higher IOP measurements than those of GAT [19, 20]. The dynamic contour tonometer is less influenced by central corneal thickness and is also more likely to show higher IOPs than GAT [21, 22]. Therefore, while further studies have been investigating the characteristics of these tonometers, GAT is still considered as the gold standard because of its clinically proven accuracy and availability.

Measurements with GAT are usually made to the 1 mmHg level with a sGAT’s scale marked at every 2 mmHg. If a measurement lies between the lines on the scale, the measurement is subjectively judged by the examiner. Thus, the results may differ between examiners. IOP measurements by dGAT are displayed to the 0.1 mmHg level, resulting in more objective measurements. Another benefit of dGAT is that IOP data on the display can be easily read in a dark room (Figure 1).

Previous studies have reported that dGAT yields highly reproducible results and there is a significant positive correlation between sGAT and dGAT measurements [23, 24]. Similarly, in the present study, we observed significant positive correlation between sGAT and dGAT measurements (Figure 2 and Table 2). Furthermore, we observed a positive correlation between sGAT and dGAT results even when the subjects were divided into groups based on the mean tonometry reading (Table 2). Before the present study, the dispersion in measurements based on differences (maximum–minimum) has not been investigated. This study demonstrated that dGAT yields significantly smaller differences (maximum–minimum) when sets of three consecutive tonometry readings are analyzed. The amount of dispersion was smaller presumably due to the 0.1 mmHg resolution. We also found that there was no trend for skew in the sGAT and dGAT readings based on the Bland-Altman plot (Figure 3). These results may be a reflection of the fact that sGAT and dGAT are based on the same principles to measure IOP.

Even in patients with equal IOP (zero left-right difference) with sGAT, dGAT detected IOP differences between the left and right eyes. Although the differences were small ( mmHg), this result indicates that even small differences in IOP that could not be detected by sGAT can be detected by dGAT. This characteristic of dGAT may be useful when evaluating the effects of medications, especially in patients with normal-tension glaucoma or those who achieved low IOP with treatment. In such patients, changes in IOP too small to be detected by the 1 mmHg resolution with sGAT can be observed with dGAT with 0.1 mmHg resolution.

In conclusion, dGAT, which shares the same principles for IOP measurement with sGAT, can provide more accurate IOP data with high reproducibility and less dispersion due to its 0.1 mmHg scale. Thus, dGAT will enable the more refined IOP evaluation required for clinical management of patients with normal-tension glaucoma and patients with progressive visual field loss despite low IOP.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgment

The abstract of this paper was published in the first Asia-Pacific Glaucoma Congress (APGC 2012). This work was supported by a Grant-in-Aid for Scientific Research (Kakenhi) no. 23592556 from the Japan Society for the Promotion of Science.

References

  1. M. A. Kass, D. K. Heuer, E. J. Higginbotham et al., “The Ocular Hypertension Treatment Study: a randomized trial determines that topical ocular hypotensive medication delays or prevents the onset of primary open-angle glaucoma,” Archives of Ophthalmology, vol. 120, no. 6, pp. 701–713, 2002. View at: Publisher Site | Google Scholar
  2. M. O. Gordon, J. A. Beiser, J. D. Brandt et al., “The Ocular Hypertension Treatment Study: baseline factors that predict the onset of primary open-angle glaucoma,” Archives of Ophthalmology, vol. 120, no. 6, pp. 714–720, 2002. View at: Publisher Site | Google Scholar
  3. M. C. Leske, A. Heijl, L. Hyman, and B. Bengtsson, “Bengtsson B. Early manifest glaucoma trial: design and baseline data,” Ophthalmology, vol. 106, no. 11, pp. 2144–2153, 1999. View at: Publisher Site | Google Scholar
  4. A. Heijl, M. C. Leske, B. Bengtsson, L. Hyman, and M. Hussein, “Reduction of intraocular pressure and glaucoma progression: results from the Early Manifest Glaucoma Trial,” Archives of Ophthalmology, vol. 120, no. 10, pp. 1268–1279, 2002. View at: Publisher Site | Google Scholar
  5. M. C. Leske, A. Heijl, M. Hussein, B. Bengtsson, L. Hyman, and E. Komaroff, “Factors for glaucoma progression and the effect of treatment: the early manifest glaucoma trial,” Archives of Ophthalmology, vol. 121, no. 1, pp. 48–56, 2003. View at: Publisher Site | Google Scholar
  6. B. Bengtsson, M. C. Leske, L. Hyman, A. Heijl, and Early Manifest Glaucoma Trial Group, “Fluctuation of intraocular pressure and glaucoma progression in the early manifest glaucoma trial,” Ophthalmology, vol. 114, no. 2, pp. 205–209, 2007. View at: Publisher Site | Google Scholar
  7. Collaborative Normal-Tension Glaucoma Study Group, “Comparison of glaucomatous progression between untreated patients with normal-tension glaucoma and patients with therapeutically reduced intraocular pressures,” The American Journal of Ophthalmology, vol. 126, no. 4, pp. 487–497, 1998. View at: Publisher Site | Google Scholar
  8. D. R. Anderson, S. M. Drance, and M. Schulzer, “Natural history of normal-tension glaucoma,” Ophthalmology, vol. 108, pp. 247–253, 2001. View at: Google Scholar
  9. D. R. Anderson, S. M. Drance, and M. Schulzer, “Factors that predict the benefit of lowering intraocular pressure in normal tension glaucoma,” American Journal of Ophthalmology, vol. 136, no. 5, pp. 820–829, 2003. View at: Publisher Site | Google Scholar
  10. D. E. Gaasterland, F. Ederer, E. K. Sullivan, J. Caprioli, and M. N. Cyrlin, “Advanced glaucoma intervention study: 2. Visual field test scoring and reliability,” Ophthalmology, vol. 101, no. 8, pp. 1445–1455, 1994. View at: Publisher Site | Google Scholar
  11. D. E. Gaasterland, F. Ederer, A. Beck et al., “The Advanced Glaucoma Intervention Study (AGIS): 7. The relationship between control of intraocular pressure and visual field deterioration,” The American Journal of Ophthalmology, vol. 130, no. 4, pp. 429–440, 2000. View at: Publisher Site | Google Scholar
  12. K. Nouri-Mahdavi, D. Hoffman, A. L. Coleman et al., “Predictive factors for glaucomatous visual field progression in the Advanced Glaucoma Intervention Study,” Ophthalmology, vol. 111, no. 9, pp. 1627–1635, 2004. View at: Publisher Site | Google Scholar
  13. J. Caprioli and A. L. Coleman, “Intraocular pressure fluctuation. a risk factor for visual field progression at low intraocular pressures in the advanced glaucoma intervention study,” Ophthalmology, vol. 115, no. 7, pp. 1123.e3–1129.e3, 2008. View at: Publisher Site | Google Scholar
  14. B. C. Chauhan, F. S. Mikelberg, A. G. Balaszi, R. P. LeBlanc, M. R. Lesk, and G. E. Trope, “Canadian glaucoma study: 2. Risk factors for the progression of open-angle glaucoma,” Archives of Ophthalmology, vol. 126, no. 8, pp. 1030–1036, 2008. View at: Publisher Site | Google Scholar
  15. P. A. Tonnu, T. Ho, K. Sharma, E. White, C. Bunce, and D. F. Garway-Heath, “A comparison of four methods of tonometry: method agreement and interobserver variability,” The British Journal of Ophthalmology, vol. 89, no. 7, pp. 847–850, 2005. View at: Publisher Site | Google Scholar
  16. G. S. Horowitz, J. Byles, J. Lee, and C. D'Este, “Comparison of the Tono-Pen and Goldman tonometer for measuring intraocular pressure in patients with glaucoma,” Clinical and Experimental Ophthalmology, vol. 32, no. 6, pp. 584–589, 2004. View at: Publisher Site | Google Scholar
  17. F. C. Hollows and P. A. Graham, “Intra-ocular pressure, glaucoma, and glaucoma suspects in a defined population,” British Journal of Ophthalmology, vol. 50, no. 10, pp. 570–586, 1966. View at: Publisher Site | Google Scholar
  18. A. J. Buller, K. Chatzinikolas, N. Giannopoulos et al., “Digit preference in Goldmann applanation tonometry: the hedgehog effect,” American Journal of Ophthalmology, vol. 140, no. 3, pp. 527–529, 2005. View at: Publisher Site | Google Scholar
  19. M. E. Iliev, D. Goldblum, K. Katsoulis, C. Amstutz, and B. Frueh, “Comparison of rebound tonometry with Goldmann applanation tonometry and correlation with central corneal thickness,” British Journal of Ophthalmology, vol. 90, no. 7, pp. 833–835, 2006. View at: Publisher Site | Google Scholar
  20. J. M. Martinez-de-la-Casa, J. Garcia-Feijoo, A. Castillo, and J. Garcia-Sanchez, “Reproducibility and clinical evaluation of rebound tonometry,” Investigative Ophthalmology and Visual Science, vol. 46, no. 12, pp. 4578–4580, 2005. View at: Publisher Site | Google Scholar
  21. E. Schneider and F. Grehn, “Intraocular pressure measurement—comparison of dynamic contour tonometry and goldmann applanation tonometry,” Journal of Glaucoma, vol. 15, no. 1, pp. 2–6, 2006. View at: Publisher Site | Google Scholar
  22. M. Pache, S. Wilmsmeyer, S. Lautebach, and J. Funk, “Dynamic contour tonometry versus Goldmann applanation tonometry: a comparative study,” Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 243, no. 8, pp. 763–767, 2005. View at: Publisher Site | Google Scholar
  23. L. Morales-Fernandez, J. M. Martinez-de-la-Casa, J. Garcia-Feijoo, F. Saenz-Frances, E. Santos, and J. Garcia-Sanchez, “Reproducibility of the new Goldmann AT900D digital tonometer,” Journal of Glaucoma, vol. 21, no. 3, pp. 186–188, 2012. View at: Publisher Site | Google Scholar
  24. M. Egli, D. Goldblum, A. Kipfer et al., “Assessment of a new Goldmann applanation tonometer,” British Journal of Ophthalmology, vol. 96, no. 1, pp. 42–46, 2012. View at: Publisher Site | Google Scholar

Copyright © 2014 Yuta Sakaue et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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