CLINICAL SCIENCE

Comparison of Central Corneal Thickness, Thinnest Corneal Thickness, Anterior Chamber Depth, and Simulated Keratometry Using Galilei, Pentacam, and Sirius Devices Mustafa A. Anayol, MD,* Emre Güler, MD,† Ramazan Ya g cı, MD,‡ Mehmet A. S¸ ekero g lu, MD,* Meltem Yılmazo g lu, MD,* Hakan Tırhıs¸, MD,* Ali E. Kulak, MD,† and Pelin Yılmazbas¸, MD*

Purpose: The aim was to evaluate the agreement in the central corneal thickness (CCT), thinnest corneal thickness (TCT), anterior chamber depth (ACD), and mean simulated keratometry (simK) measurements using Pentacam, Galilei, and Sirius Scheimpflug systems in normal eyes.

Methods: Anterior segment measurements were performed with Pentacam, Galilei, and Sirius devices in 32 healthy subjects. The right eye of each participant was selected. Measurements obtained with the 3 systems were compared using repeatedmeasures analysis of variance and Bonferroni multiple comparisons test.

Results: Analysis of variance determined a significant difference in the anterior segment measurements of CCT, TCT, ACD, and simK between the 3 devices (P , 0.001). Pairwise comparisons of CCT and TCT measurements were significantly different except for the comparison between Pentacam and Sirius. All pairwise comparisons for ACD were statistically significant. The pairwise comparison results for simK values showed that the Galilei and Sirius systems demonstrated better agreement with each other than with Pentacam. Conclusions: The results of this study suggest that the Pentacam, Galilei, and Sirius Scheimpflug systems should not be accepted as interchangeable for CCT, TCT, ACD, and simK in healthy subjects. Key Words: central corneal thickness, thinnest corneal thickness, anterior chamber depth, simulated keratometry, Pentacam, Galilei, Sirius (Cornea 2014;33:582–586)

Received for publication January 13, 2014; revision received February 23, 2014; accepted February 25, 2014. Published online ahead of print April 23, 2014. From the *Department of Ophthalmology, Ulucanlar Eye Training and Research Hospital, Ankara, Turkey; †Department of Ophthalmology, Turgut Özal University School of Medicine, Ankara, Turkey; and ‡Department of Ophthalmology, Pamukkale University School of Medicine, Denizli, Turkey. The authors have no funding or conflicts of interest to disclose. Reprints: Emre Güler, Department of Ophthalmology, Turgut Özal University School of Medicine, Alparslan Türkes Cad, No. 57, 06510 Emek, Ankara, Turkey (e-mail: [email protected]). Copyright © 2014 by Lippincott Williams & Wilkins

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ccurate measurements of keratometry, corneal thickness, and anterior chamber depth (ACD) are crucial to the design and ultimate success of vision corrective procedures such as refractive and cataract surgery.1–5 The introduction of Scheimpflug cameras into clinical practice has significantly improved capabilities of imaging the anterior eye segment that were not possible until a few years ago. In 2002, the first rotating Scheimpflug camera, the Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany),6,7 was introduced. More recently, the Galilei (Ziemer Ophthalmic Systems AG, Zurich, Switzerland)8 and the Sirius (Costruzione Strumenti Oftalmici, Florence, Italy),9 combination of Scheimpflug camera with a Placido topography system, were introduced. To acquire keratometric data of the anterior corneal surface, Pentacam uses only the Scheimpflug images, whereas the Galilei and Sirius use the Placido disk.10–12 These noncontact methods are able to assess many anterior segment parameters including the total corneal dioptric power (ie, the dioptric power of the whole cornea, including the anterior and posterior surfaces), corneal pachymetry, the ACD, and volume. Although other studies have assessed the agreement of the Pentacam measurements with Galilei separately12–14 and the agreement of the Pentacam with Sirius,15,16 it has not been clear whether the results of these devices are comparable and whether they can be used interchangeably. Therefore, we compared the anterior segment parameters measured with Pentacam, Galilei, and Sirius in healthy corneas.

MATERIALS AND METHODS This prospective study was managed in accordance with the Helsinki Declaration. All participants were informed about the aim of the study and had given informed consent. All of the subjects included in this study were healthy except for any refractive error. The exclusion criteria were any ocular or systemic disease or contact lens usage within 2 weeks or history of any ocular surgery or history of any ocular trauma. The right eye of each participant was selected. In 2 cases Galilei and in 1 case Pentacam was unable to obtain a scan of acceptable quality after 5 attempts, whereas the sequential measurements obtained by the other devices were acceptable for these cases. Therefore, we included the left eye of these Cornea  Volume 33, Number 6, June 2014

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patients in the study. The study was approved by the local ethics committee. All measurements were taken with a nondilated pupil in identical lighting conditions. Measurements were obtained sequentially (approximately 5 minutes apart) using the Pentacam, Galilei, and Sirius Scheimpflug systems by different investigators who were masked to the results of the previous measurements obtained from each device. For each subject, the orders of the devices and the operators were both selected randomly. The subjects were instructed to blink immediately before each measurement. All devices provide a quality score of individual measurements, and they were calibrated during the course of the study. The high-resolution Pentacam system uses a rotating Scheimpflug camera (180 degrees) and a monochromatic slitlight source (blue light–emitting diode at 475 nm) that rotate together around the optical axis of the eye to calculate a 3-dimensional (3-D) model of the anterior segment. The system has two 3-D scanning modes. One is a typical 3-D scan that takes 50 images in 2 seconds, and the other is a 3-D high-resolution cornea-scanning mode that takes 50 images in 1 second. Overall, 138,000 true elevation points are recorded. In this study, we used the typical 3-D scan method to access 50 images for all subjects. The Galilei uses a dual rotating Scheimpflug camera integrated with a Placido disc topographer. The device’s software (Galilei G2, version 5.2.1) was used to perform measurements. The flash illumination is the output from a 475-nm wavelength blue light–emitting diode (ultraviolet free), and it measures more than 122,000 data points per scan. The Sirius system is a new topography device, which uses the principles of Scheimpflug photography and enables the acquisition and processing of 25 radial sections of the cornea and anterior chamber within a few seconds. The following parameters were measured by both devices and compared in this study: the central corneal

Comparison of Galilei, Pentacam, and Sirius Devices

thickness (CCT), thinnest corneal thickness (TCT), ACD, and mean simulated keratometry (simK). The mean K is calculated from the K values along the flattest meridian and the K value in the steepest meridian. All statistical studies were performed with SPSS for Windows software (version 15.0; SPSS Inc). Variables were described as mean 6 standard error of the mean (SEM). Measurements obtained with the 3 different methods were compared using repeated-measures analysis of variance (ANOVA). If the ANOVA revealed a significant interaction, post hoc analysis was performed using the Bonferroni multiple comparisons test when applicable. A P , 0.05 was considered statistically significant.

RESULTS Thirty-two eyes of 32 volunteers (21 male and 11 female) were evaluated in this prospective study. The mean age of the participants was 29.31 6 12.47 (range, 14–60) years.

Agreement of CCT Measurements CCT was measured using Galilei, Pentacam, and Sirius with mean 6 SEM of 543.02 6 4.15 mm, 526.92 6 4.65 mm, and 526.20 6 4.40 mm, respectively, and a repeatedmeasures ANOVA determined that there was a significant difference between the 3 devices (P , 0.001). Galilei overestimated CCT measurements compared with both Pentacam and Sirius (Table 1). All pairwise comparisons using the Bonferroni correction for CCT measurements were significantly different except for the comparison between Pentacam and Sirius (P = 1.0). Ninety-five percent limits of agreement of CCT values showed that the Pentacam and Sirius systems demonstrated better agreement with each other than with the Galilei (Table 2).

TABLE 1. Summary of CCT, TCT, ACD, and Sim K Measurements for Galilei, Pentacam, and Sirius CCT Mean 6 SEM, Median, mm Range, mm TCT Mean 6 SEM, Median, mm Range, mm ACD Mean 6 SEM, Median, mm Range, mm SimK Mean 6 SEM, Median, D Range, D

Galilei

Pentacam

Sirius

P*

mm

543.02 6 4.15 540.50 490–619

526.92 6 4.65 529.50 429–598

526.20 6 4.40 527.00 435–602

,0.001

mm

529.82 6 4.27 529.5 478–608

524.32 6 4.44 526 469–597

524.29 6 4.13 523 469–599

,0.001

mm

3.25 6 0.03 3.31 2.49–3.88

3.12 6 0.03 3.17 2.37–3.80

3.16 6 0.03 3.21 2.40–3.83

,0.001

D

43.88 6 0.19 43.87 40.84–46.67

43.33 6 0.24 43.55 39.30–47.80

43.83 6 0.20 43.90 40.70–46.86

,0.001

*Repeated-measures ANOVA.

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TABLE 2. Mean Difference, SEM, and Limits of Agreement in CCT Measurements for Galilei, Pentacam, and Sirius

Measurement

Mean Difference 6 SEM, mm

95% Limit of Agreement, mm

P*

Galilei–Pentacam Galilei–Sirius Pentacam–Sirius

13.93 6 0.88 14.66 6 0.69 0.73 6 0.93

11.74 to 16.12 12.96 to 16.37 21.50 to 3.02

,0.001 ,0.001 1.0

*Adjustment for multiple comparisons: Bonferroni.

TABLE 4. Mean Difference, SEM, and Limits of Agreement in ACD Measurements for Galilei, Pentacam, and Sirius

Measurement

Mean Difference 6 SEM, mm

95% Limit of Agreement, mm

P*

Galilei–Pentacam Galilei–Sirius Sirius–Pentacam

0.11 6 0.008 0.07 6 0.007 0.04 6 0.007

0.09 –0.13 0.05 –0.09 0.02 –0.06

,0.001 ,0.001 ,0.001

*Adjustment for multiple comparisons: Bonferroni.

Agreement of TCT Measurements TCT was measured using Galilei, Pentacam, and Sirius with mean 6 SEM of 529.82 6 4.27 mm, 524.32 6 4.44 mm, and 524.29 6 4.13 mm, respectively, and a repeated-measures ANOVA determined that there was a significant difference between the 3 devices (P , 0.001). Galilei overestimated TCT measurements compared with both Pentacam and Sirius (Table 1). All pairwise comparisons using the Bonferroni correction for TCT measurements were significantly different except for the comparison between Pentacam and Sirius (P = 1.0). Ninety-five percent limits of agreement of TCT values showed that the Pentacam and Sirius systems demonstrated better agreement with each other than with the Galilei (Table 3).

correction test demonstrated that mean simK measurements were slightly closer between the Galilei and Sirius (P = 0.488), whereas Pentacam-Galilei and Pentacam-Sirius comparisons for simK showed a significant difference (P , 0.01). Ninety-five percent limits of agreement of simK values showed that the Galilei and Sirius systems demonstrated better agreement with each other than with Pentacam (Table 5).

DISCUSSION

SimK was measured using Galilei, Pentacam, and Sirius with mean 6 SEM of 43.88 6 0.19 diopters (D), 43.33 6 0.24 D, and 43.83 6 0.20 D, respectively, and a repeated-measures ANOVA determined that there was significant difference between the 3 devices (P , 0.001) (Table 1). Bonferroni

The importance of definitive measurement of CCT, TCT, simK, and ACD has gradually increased because of developments in corneal refractive surgeries and phakic intraocular lens (IOL) implantation procedures.14 In this study, we compared the measurements of those anterior segment parameters using 3 different Scheimpflug-based optical devices to decide whether there is sufficient agreement for the devices to be used interchangeably in routine clinical practice. CCT measurements are important in the diagnosis of a variety of corneal pathologies, the accurate evaluation of intraocular pressure measurements, and the qualification of patients regarding refractive surgeries. The observations in this study suggest that pachymetry measurements obtained by different devices cannot be used interchangeably. We have found significantly higher CCT values with the Galilei than those obtained by both the Sirius and Pentacam systems as it was reported by Huang et al.17 In a previous study, Jahadi Hosseini et al12 reported good concordance between CCT measurements determined by the Galilei and Pentacam. In this study, all pairwise comparisons for CCT measurements were significantly different except for the comparison between Pentacam and Sirius. TCT is one of the main variables required to detect primary ectasias.18 In a previous study, the TCT was found to

TABLE 3. Mean Difference, SEM, and Limits of Agreement in TCT Measurements for Galilei, Pentacam, and Sirius

TABLE 5. Mean Difference, SEM, and Limits of Agreement in SimK Measurements for Galilei, Pentacam, and Sirius

Agreement of ACD Measurements ACD was measured using Galilei, Pentacam, and Sirius with mean 6 SEM of 3.22 6 0.03 mm, 3.12 6 0.03 mm, and 3.16 6 0.03 mm, respectively, and a repeated-measures ANOVA determined that the difference was statistically significant between the 3 devices (P , 0.001). Galilei overestimated ACD measurements compared with the other 2 devices (Table 1). Bonferroni correction test revealed that all pairwise comparisons for ACD were statistically significant (P , 0.001). Similarly, all pairwise comparisons of ACD showed large 95% limits of agreement (Table 4).

Agreement of Mean SimK Measurements

Measurement

Mean Difference 6 SEM, mm

95% Limit of Agreement, mm

P*

Galilei–Pentacam Galilei–Sirius Sirius–Pentacam

5.50 6 0.87 5.53 6 0.71 20.03 6 1.06

3.34 to 7.65 3.76 to 7.30 22.66 to 2.59

,0.001 ,0.001 1.0

*Adjustment for multiple comparisons: Bonferroni.

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Measurement

Mean Difference 6 SEM, mm

95% Limit of Agreement, mm

P*

Galilei–Pentacam Galilei–Sirius Sirius–Pentacam

0.41 6 0.10 20.03 6 0.02 0.45 6 0.10

0.17 to 0.66 20.09 to 0.02 0.20 to 0.70

,0.001 0.488 ,0.001

*Adjustment for multiple comparisons: Bonferroni.

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be the most useful parameter for distinguishing eyes with different stages of keratoconus.19 The findings in this study suggest that TCT measurements obtained by different devices cannot be used interchangeably because the Galilei significantly measured not only CCT values higher but TCT values as well, than both Sirius and Pentacam systems. However, no statistically significant difference was observed between Pentacam and Sirius. ACD measurement has become necessary in cataract and refractive surgery for sophisticated IOL power calculation methods and phakic implantations of IOL.20 In a previous study, Salouti et al13 evaluated the agreement in ACD measurements of normal subjects obtained from 3 anterior segment analyzers: Orbscan, Pentacam, and Galilei. They found that the ACD measurements of Orbscan were significantly higher when compared with Pentacam and Galilei and suggested that Orbscan is not interchangeable with Galilei or Pentacam in every clinical application. However, in the previous study, differences of ACD measurements obtained with Pentacam and Galilei were not statistically significant; hence, the interchangeability of both devices could be acceptable. In our study, we found significant differences in ACD measurements between Galilei, Pentacam, and Sirius. Additionally, Galilei yielded larger ACD measurements compared with the other 2 devices, and all pairwise comparisons for ACD were statistically significant. Therefore, we consider that these 3 devices may not be used interchangeably in ACD measurements. Accurate keratometry measurements are extremely important in refractive surgery and for IOL calculation.21 In a previous study, Wang et al22 reported good concordance between anterior corneal power measurements determined by Pentacam and Sirius. In this study, simK measurements from all the 3 devices produced significantly different mean values. Similarly, all pairwise comparison results for simK were significantly different. Clinical significance measures whether a treatment was effective enough to change a patient’s diagnostic label.23 However, statistical significance does not produce any information about clinical significance.24 Although small differences may be statistically significant, they have minimal clinical significance. In this study, statistical significance was observed for all measurements of 3 devices; however, the only clinical significance may be considered for the measurements of CCT and TCT. The Galilei overestimated the measurements of CCT and TCT approximately 12 and 5 mm, respectively, compared with Pentacam and Sirius. These differences may have clinical significance in the diagnosis and long-term follow-up of corneal primary and iatrogenic ectasias. In this study, the CCT, TCT, ACD, and simK values obtained by the Galilei, Pentacam, and Sirius topographers were sufficiently different that the 3 devices could not be considered equivalent. Because of the lack of a true gold standard for corneal tomography measurements, the interpretation of differences between Pentacam, Sirius, and Galilei is statistically significant. Because the true value is unknown, it is not possible to conclude which device obtains the most accurate measurements, and therefore, it Ó 2014 Lippincott Williams & Wilkins

Comparison of Galilei, Pentacam, and Sirius Devices

is not possible to recommend one device over the others at present. This study revealed significant differences in CCT, TCT, ACD, and simK measurements using Galilei, Pentacam, and Sirius in healthy subjects. Therefore, these devices should not be considered as interchangeable for CCT, TCT, ACD, and simK measurements in healthy subjects. REFERENCES 1. Javaloy J, Vidal MT, Villada JR, et al. Comparison of four corneal pachymetry techniques in corneal refractive surgery. J Refract Surg. 2004;20:29–34. 2. Wang L, Shirayama M, Koch DD. Repeatability of corneal power and wavefront aberration measurements with a dual-Scheimpflug Placido corneal topographer. J Cataract Refract Surg. 2010;36: 425–430. 3. Savini G, Barboni P, Carbonelli M, et al. Comparison of methods to measure corneal power for intraocular lens power calculation using a rotating Scheimpflug camera. J Cataract Refract Surg. 2013;39: 598–604. 4. Norrby S. Sources of error in intraocular lens power calculation. J Cataract Refract Surg. 2008;34:368–376. 5. Olsen T. Prediction of intraocular lens position after cataract extraction. J Cataract Refract Surg. 1986;12:376–379. 6. Miranda MA, Radhakrishnan H, O’Donnell C. Repeatability of corneal thickness measured using an Oculus Pentacam. Optom Vis Sci. 2009;86: 266–272. 7. McAlinden C, Khadka J, Pesudovs K. A comprehensive evaluation of the precision (repeatability and reproducibility) of the Oculus Pentacam HR. Invest Ophthalmol Vis Sci. 2011;52:7731–7737. 8. Savini G, Carbonelli M, Barboni P, et al. Repeatability of automatic measurements performed by a dual Scheimpflug analyzer in unoperated and post-refractive surgery eyes. J Cataract Refract Surg. 2011;37: 302–309. 9. Savini G, Barboni P, Carbonelli M, et al. Repeatability of automatic measurements by a new Scheimpflug camera combined with Placido topography. J Cataract Refract Surg. 2011;37:1809–1816. 10. Menassa N, Kaufmann C, Goggin M, et al. Comparison and reproducibility of corneal thickness and curvature readings obtained by the Galilei and the Orbscan II analysis systems. J Cataract Refract Surg. 2008;34: 1742–1747. 11. Montalbán R, Piñero DP, Javaloy J, et al. Intrasubject repeatability of corneal morphology measurements obtained with a new Scheimpflug photography-based system. J Cataract Refract Surg. 2012;38: 971–977. 12. Jahadi Hosseini HR, Katbab A, Khalili MR, et al. Comparison of corneal thickness measurements using Galilei, HR Pentacam, and ultrasound. Cornea. 2010;29:1091–1095. 13. Salouti R, Nowroozzadeh MH, Zamani M, et al. Comparison of anterior and posterior elevation map measurements between 2 Scheimpflug imaging systems. J Cataract Refract Surg. 2009;35: 856–862. 14. Park SH, Choi SK, Lee D, et al. Corneal thickness measurement using Orbscan, Pentacam, Galilei, and ultrasound in normal and postfemtosecond laser in situ keratomileusis eyes. Cornea. 2012;31: 978–982. 15. De la Parra-Colín P, Garza-León M, Barrientos-Gutierrez T. Repeatability and comparability of anterior segment biometry obtained by the Sirius and the Pentacam analyzers. Int Ophthalmol. 2014;34:27–33. 16. Nasser CK, Singer R, Barkana Y, et al. Repeatability of the Sirius imaging system and agreement with the Pentacam HR. J Refract Surg. 2012; 28:493–497. 17. Huang J, Ding X, Savini G, et al. A comparison between Scheimpflug imaging and optical coherence tomography in measuring corneal thickness. Ophthalmology. 2013;120:1951–1958. 18. Li Y, Meisler DM, Tang M, et al. Keratoconus diagnosis with optical coherence tomography pachymetry mapping. Ophthalmology. 2008;115: 2159–2166.

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19. Demir S, Ortak H, Yeter V, et al. Mapping corneal thickness using dualscheimpflug imaging at different stages of keratoconus. Cornea. 2013; 32:1470–1474. 20. Holladay JT, Prager TC, Chandler TY, et al. A three-part system for refining intraocular lens power calculations. J Cataract Refract Surg. 1988;14:17–24. 21. Lee AC, Qazi MA, Pepose JS. Biometry and intraocular lens power calculation. Curr Opin Ophthalmol. 2008;19:13–17. 22. Wang Q, Savini G, Hoffer KJ, et al. A comprehensive assessment of the precision and agreement of anterior corneal power

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measurements obtained using 8 different devices. PLoS One. 2012;7:e45607. 23. Peterson L. “Clinical” significance: “Clinical” significance and “Practical” significance are not the Same Things. Online submission. Paper presented at: Annual Meeting of the Southwest Educational Research Association; February 7, 2008; New Orleans, LA. 24. Haase RF, Ellis MV, Ladany N. Multiple criteria for evaluating the magnitude of experimental effects. J Couns Psychol. 1989;36: 511–516.

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Comparison of central corneal thickness, thinnest corneal thickness, anterior chamber depth, and simulated keratometry using galilei, Pentacam, and Sirius devices.

The aim was to evaluate the agreement in the central corneal thickness (CCT), thinnest corneal thickness (TCT), anterior chamber depth (ACD), and mean...
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