Journal of Refractive Surgery

Original Article Supplemental Data

Repeatability, Reproducibility, and Agreement Between Three Different Scheimpflug Systems in Measuring Corneal and Anterior Segment Biometry

Julio C. Hernández-Camarena, MD; Patricia Chirinos-Saldaña, MD; Alejandro Navas, MD, MSc; Arturo Ramirez-Miranda, MD; Angie de la Mota, MD; Aida Jimenez-Corona, MD, PhD; Enrique O. Graue-Hernández, MD, PhD

Abstract

PURPOSE:

To assess the reliability of three different Scheimpflug systems and their agreement.

METHODS:

Eighty-four eyes of 42 patients were examined with three Scheimpflug devices: the Galilei G2 Dual Scheimpflug Analyzer (Ziemer Ophthalmic Systems AG, Port, Switzerland), Pentacam HR system (Oculus Optikgeräte GmbH, Wetzlar, Germany), and Sirius 3D imaging system (Costruzione Strumenti Oftalmici, Florence, Italy). The central corneal thickness, maximum anterior and posterior corneal elevation, anterior radius of curvature, total higher-order aberrations, and anterior chamber depth were evaluated. Repeatability and reproducibility were evaluated using coefficients of variation and intraclass correlation coefficients. Interdevice agreement was assessed by Bland–Altman comparison analysis.

RESULTS:

The three Scheimpflug systems had excellent repeatability for central corneal thickness, anterior radius of curvature, and anterior chamber depth (coefficients of variation being less than 1%). Repeatability for anterior and posterior corneal evaluation was good for the Pentacam HR and Galilei G2 (coefficients of variation < 10%) and excellent for the Sirius 3D (coefficients of variation = 0). Reproducibility was excellent in the three devices, (intraclass correlation coefficient of more than 0.9). Interdevice agreement was excellent (P > .05) for anterior radius of curvature, central corneal thickness, and anterior chamber depth, but was poor (P < .05) for corneal elevation and higher-order aberrations.

CONCLUSIONS:

Reliability was good to excellent in the three devices for all measured variables. Interdevice agreement analysis suggests that measurements for anterior radius of curvature, central corneal thickness, and anterior chamber depth, but not for maximum anterior and posterior corneal elevation and total higher-order aberrations, from the Sirius 3D and Galilei G2 can be interchangeable with the Pentacam HR.

[J Refract Surg. 2014;30(9):616–621.]

From the Department of Cornea and Refractive Surgery, Instituto de Oftalmologia “Conde de Valenciana,” Mexico City, Mexico.

The authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (JCH-C, PC-S, AN, EOG-H); data collection (JCH-C, PC-S, ADLM, EOG-H); analysis and interpretation of data (JCH-C, AN, AR-M, ADLM, AJ-C, EOG-H); drafting of the manuscript (JCH-C, AR-M, EOG-H); critical revision of the manuscript (JCH-C, AN, AR-M, AJ-C, EOG-H); statistical expertise (JCH-C, AN, AJ-C, EOG-H); supervision (AN, EOG-H)

Correspondence: Enrique O. Graue-Hernández, MD, Department of Cornea and Refractive Surgery, Instituto de Oftalmologia “Conde de Valenciana”, Chimalpopoca 14, Cuauhtémoc 06800, Mexico City, Mexico. E-mail: egraueh@gmail.com

Received: November 18, 2013
Accepted: May 30, 2014
Posted Online: September 05, 2014

Abstract

PURPOSE:

To assess the reliability of three different Scheimpflug systems and their agreement.

METHODS:

Eighty-four eyes of 42 patients were examined with three Scheimpflug devices: the Galilei G2 Dual Scheimpflug Analyzer (Ziemer Ophthalmic Systems AG, Port, Switzerland), Pentacam HR system (Oculus Optikgeräte GmbH, Wetzlar, Germany), and Sirius 3D imaging system (Costruzione Strumenti Oftalmici, Florence, Italy). The central corneal thickness, maximum anterior and posterior corneal elevation, anterior radius of curvature, total higher-order aberrations, and anterior chamber depth were evaluated. Repeatability and reproducibility were evaluated using coefficients of variation and intraclass correlation coefficients. Interdevice agreement was assessed by Bland–Altman comparison analysis.

RESULTS:

The three Scheimpflug systems had excellent repeatability for central corneal thickness, anterior radius of curvature, and anterior chamber depth (coefficients of variation being less than 1%). Repeatability for anterior and posterior corneal evaluation was good for the Pentacam HR and Galilei G2 (coefficients of variation < 10%) and excellent for the Sirius 3D (coefficients of variation = 0). Reproducibility was excellent in the three devices, (intraclass correlation coefficient of more than 0.9). Interdevice agreement was excellent (P > .05) for anterior radius of curvature, central corneal thickness, and anterior chamber depth, but was poor (P < .05) for corneal elevation and higher-order aberrations.

CONCLUSIONS:

Reliability was good to excellent in the three devices for all measured variables. Interdevice agreement analysis suggests that measurements for anterior radius of curvature, central corneal thickness, and anterior chamber depth, but not for maximum anterior and posterior corneal elevation and total higher-order aberrations, from the Sirius 3D and Galilei G2 can be interchangeable with the Pentacam HR.

[J Refract Surg. 2014;30(9):616–621.]

From the Department of Cornea and Refractive Surgery, Instituto de Oftalmologia “Conde de Valenciana,” Mexico City, Mexico.

The authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (JCH-C, PC-S, AN, EOG-H); data collection (JCH-C, PC-S, ADLM, EOG-H); analysis and interpretation of data (JCH-C, AN, AR-M, ADLM, AJ-C, EOG-H); drafting of the manuscript (JCH-C, AR-M, EOG-H); critical revision of the manuscript (JCH-C, AN, AR-M, AJ-C, EOG-H); statistical expertise (JCH-C, AN, AJ-C, EOG-H); supervision (AN, EOG-H)

Correspondence: Enrique O. Graue-Hernández, MD, Department of Cornea and Refractive Surgery, Instituto de Oftalmologia “Conde de Valenciana”, Chimalpopoca 14, Cuauhtémoc 06800, Mexico City, Mexico. E-mail: egraueh@gmail.com

Received: November 18, 2013
Accepted: May 30, 2014
Posted Online: September 05, 2014

The precise measurement of anterior chamber and corneal biometry parameters is essential for the pre-operative evaluation for cataract and refractive surgery. The accuracy of these biometric parameters is critical to select the most suitable refractive procedure for each patient, to identify risk factors for the development of intraoperative and postoperative complications, and to assess possible future additional surgical interventions. Hence, qualitative information regarding the anterior segment and corneal anatomy and morphology can affect surgical outcome in selecting the dioptric power of intraocular lens in patients undergoing cataract surgery or the appropriate size and power of phakic intraocular lens1,2 and sizing of the corneal implant rings for the treatment of keratoconus.3

Devices incorporating the Scheimpflug principle have shown to be precise in measuring light scattering and to be reliable measuring tools to provide quantitative data of the anterior segment and corneal biometry.4 The Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) is a system based on a rotating Scheimpflug camera capable of modeling anterior chamber and corneal biometry.4 Its reliability in measuring central corneal thickness, anterior chamber depth and volume, corneal curvature and power, and anterior and posterior elevation maps has been widely validated.5–7 The Sirius 3D Scheimpflug imaging system (Costruzioni Strumenti Oftalmici, Florence, Italy) combines two mechanisms of action: the Scheimpflug rotating camera and Placido disk topography. Its repeatability measuring corneal curvature, minimal corneal thickness, and anterior chamber depth has been assessed and validated.8 Finally, the Galilei G2 Dual Scheimpflug Analyzer (Ziemer Ophthalmic Systems AG, Port, Switzerland) is composed of a revolving dual channel Scheimpflug camera combined with Placido disk technology.9

Ideally, to be considered reliable, a diagnostic test or measurement instrument should have a high repeatability and reproducibility coefficient and thus must have an excellent intraobserver and interobserver variability.10 We studied the repeatability and reproducibility of these different Scheimpflug systems (the Galilei G2, Pentacam HR, and Sirius 3D) in measuring corneal and anterior chamber biometry parameters, including central corneal thickness, maximum anterior and posterior corneal elevation, corneal keratometry values, total aberration, and anterior chamber depth, and to assess their agreement with the Pentacam HR imaging system.

Patients and Methods

Healthy individuals older than 18 years were prospectively recruited from the Department of Cornea and Refractive Surgery of the Instituto de Oftalmología “Conde de Valenciana.” Individuals with any ocular abnormality, patients with dry eye, and contact lens users were excluded. The data acquisition, study design, and methodology were carried out with the approval of the ethics committee and research board of the institution. Informed consent was obtained from all patients and the study adhered to the tenets of the Declaration of Helsinki.

All eyes were examined undilated with the three Scheimpflug devices: the Pentacam HR (software version 1.17r89), Sirius 3D Scheimpflug imaging system (software version 1.2), and Galilei G2 Dual Scheimpflug Analyzer (software version 5.2.1). Two different successive independent scans were taken of each eye by two different examiners. Each participant was asked to sit back and the joystick was fully retracted and then realigned after each scan to ensure independent measurements. Patients were allowed to blink between scans and a time period of approximately 5 minutes was used to move the patient between each Scheimpflug device. Only high-quality measurements (quality score ≥ 90%) were included for further analysis.

A full analysis of the cornea and anterior segment was obtained, including anterior chamber depth ([ACD] corneal endothelium to lens), central corneal thickness (CCT), and anterior corneal radius of curvature at 3 and 7 mm (simulated keratometry measured in diopters that are later expressed in mean keratometry values [Km]). Simulated keratometry parameters (anterior curvature) were calculated with the keratometric index, which is known from Placido topographers, and is equal to 1.3375. All instruments convert the curvature measurements obtained from the anterior corneal surface into a total corneal dioptric value using the thin lens formula (n1 – n0)/r, where n0 = refractive index of air (1.0000), n1 = refractive index of the cornea (1.3375), and r = radius in mm. Also, maximum anterior (MAE) and posterior corneal elevation (MPE) at the central 3 mm and total higher-order aberration (HOA) root mean square for a 6-mm diameter area of analysis were obtained. The values for the anterior radius of corneal curvature are calculated using the difference between the refractive index of air (n = 1) and the refractive index of corneal tissue (n = 1.376) and are then expressed in diopters. Analysis for anterior and posterior maximum corneal elevations at the central 3 mm was performed by using an 8-mm diameter area to calculate the best-fit sphere fixed to the corneal apex defined by each Scheimpflug system.

Statistical Analysis

The measured values of ACD (mm), CCT (µm), anterior corneal radii of curvature (simulated keratometry in diopters), anterior and posterior central corneal elevation measured at the center of the scan (µm), and total HOAs (root mean square in the 6-mm central corneal zone) of the three instruments were processed and analyzed using Microsoft Excel 2010 (Microsoft Corporation, Redmond, WA) and SPSS version 17 (SPSS, Inc., Chicago, IL). Repeatability of the devices was evaluated by calculating coefficients of variation (CoV) and reproducibility was assessed calculating intraclass correlation coefficient (ICC). Interdevice agreement was assessed by the Bland–Altman comparison analysis, plotting the differences between the measurements against their mean and determining the 95% limits of agreement (LoA) (mean difference ± 2 standard deviations of the differences).

Results

A total of 84 eyes of 42 patients were examined. Eighteen patients (42.85%) were women and the mean age was 31.42 ± 4.27 years (range: 19 to 42 years). Table 1 shows the median and the interquartile range for the measurement of each of the six variables analyzed in this study. Table 2 summarizes the repeatability of the devices (CoV), the reproducibility (ICC), and the interdevice agreement expressed through the Bland–Altman comparison analysis.

Median and Interquartile Range for the Measurements of Each Examined Variable

Table 1:

Median and Interquartile Range for the Measurements of Each Examined Variable

Interdevice Repeatability, Reproducibility, and Agreement Expressed Through the Bland–Altman Comparison Analysis

Table 2:

Interdevice Repeatability, Reproducibility, and Agreement Expressed Through the Bland–Altman Comparison Analysis

The three Scheimpflug systems had excellent repeatability for CCT, Km, and ACD with a CoV of less than 1% (Table 2). Repeatability for MAE and MPE was good for the Pentacam HR and Galilei G2 (CoV: 9.42% for both devices) and excellent for the Sirius 3D (CoV = 0), whereas repeatability for HOA was good for the three Scheimpflug devices. Reproducibility was excellent for the three Scheimpflug devices, with an ICC of greater than 0.9 in all of the measured variables, except for HOA measured with the Pentacam HR (ICC = 0.75). The calculated 95% LoA for Km, CCT, ACD, MAE, MPE, and HOA are shown in Figures AE (available in the online version of this article). For MAE, MPE, and total HOAs, the calculated 95% LoA and the obtained mean differences were statistically different (P < .05) when comparing the Galilei G2 and Sirius 3D with the Pentacam HR (Table 2).

Discussion

Scheimpflug-based devices have been accurate in diagnosing corneal pathologies, evaluating progression of corneal ectatic disorders, and planning refractive surgery compared to previous scanning-slit measuring devices.11,12 Recently, tomography systems have included newer technologies that allow a more accurate measurement of the posterior corneal curvature, iridocorneal angle, anterior iris, and lens.13,14 These systems enable recreations of multiple images, allowing better evaluation of elevation and thickness changes throughout the cornea, instead of recreating them from collected data of scanning slit-beam technology and Placido imaging.15,16

The question of whether the data obtained from the biometric analysis of the cornea and anterior segment with any of the commercially available Scheimpflug systems is repeatable, reproducible, and interchangeable was not completely clear until now because there are a limited number of studies comparing them.

In our study, we analyzed the repeatability and reproducibility of three different Scheimpflug systems (the Galilei G2, Pentacam HR, and Sirius 3D) and the interdevice agreement of the Sirius 3D and Galilei G2 with the Pentacam HR because the latter is an imaging system that has shown consistent and reproducible measurements of the cornea and anterior segment17–20 and is used widely in many ophthalmologic centers.

Repeatability (defined as the standard deviation of multiple measurements of the same object under the same conditions21) was excellent (CoV < 1%) in the three Scheimpflug systems for CCT, Km, and ACD; MAE and MPE repeatability assessments were good with the Pentacam HR and Galilei G2 and excellent with the Sirius 3D. HOA repeatability evaluation was good (CoV between 2.77 and 3.26) for the Pentacam HR, Sirius 3D, and Galilei G2. Reproducibility (defined as the between-examiner measurement differences) of all of the measured variables was excellent (ICC > 0.9) with the three analyzed corneal topographers, except for HOA analyzed with the Pentacam HR (ICC = 0.75, good reproducibility). Previous studies evaluating the precision of the Pentacam demonstrated high repeatability and reproducibility for keratometric readings, pachymetry maps, corneal maps, anterior chamber depth, and corneal volume.22 Excellent repeatability and reproducibility for measuring anterior and posterior corneal radius, Km, CCT, ACD, and white-to-white corneal diameter have also been reported for the Sirius8,23 and Galilei G2 Dual Scheimpflug Analyzer.19

There are a limited number of studies assessing the precision (repeatability and reproducibility) of these three Scheimpflug devices in measuring corneal elevation and HOA. Nuñez and Blanco found an excellent coefficient of repeatability for maximum anterior corneal elevation measured with the Pentacam, but reported a poor coefficient of repeatability for the radius at the point of maximum posterior elevation.24 A study evaluating the precision of the Pentacam system (software version 1.16) in measuring the posterior corneal shape demonstrated a good intrasession and intersession repeatability anterior and posterior best-fit sphere and posterior corneal elevation at 5.00 and 8.00 mm.25

Wang et al. reported excellent repeatability of corneal power and HOA using the Galilei Dual Scheimpflug Analyzer (software version 5.2.1).26 A study analyzing the Pentacam HR (software version 1.17) and Galilei (software version 5.2.1) showed a low reliability of HOA root mean square for both devices, but with the dual-camera topographer displaying better CoV and ICC.19 The repeatability of corneal first-order aberrations measured with Pentacam (software version 1.14r27) corneal topography was analyzed by Shankar et al., reporting poor coefficient of repeatability.27 As of the date of our current study, a Medline search did not report any results for studies of analyzing the precision of the Sirius 3D for wavefront aberrations.

The interdevice agreement analysis suggests that the Galilei G2 and Sirius 3D can be used interchangeably with the Pentacam HR when studying Km, CCT, and ACD, but that the results of MAE, MPE, and HOA should not be used interchangeably. As of the date of our current study, no studies evaluating the interdevice agreement of the Galilei G2 Dual Scheimpflug system and the Sirius 3D imaging system with the Pentacam HR when analyzing MAE, MPE, and HOA were found in the literature. Nasser et al. reported a variable range of interdevice differences for the parameters compared (anterior and posterior corneal radii, anterior chamber depth, and minimal corneal thickness).8 Likewise, Aramberri et al. assessed the agreement of the Pentacam HR (software version 1.17) single camera and Galilei G2 dual camera (software version 5.2.1) Scheimpflug devices in anterior segment analysis and found good agreement for most parameters (anterior and posterior cornea simulated keratometry, K flat, K steep, astigmatism magnitude and axis, J0 and J45 vectors, asphericity, central cornea and thinnest-point thicknesses, and anterior chamber depth), except total corneal power and HOA root mean square (both P < .001).19

In our study, the limits of agreement for Km, CCT, and ACD when comparing the Galilei G2 and Sirius 3D with the Pentacam HR were statistically not significant and clinically irrelevant because the mean difference in Km was less than 0.15 diopters, less than 16.2 µm for CCT, and less than 0.08 mm in ACD. These results suggest that data obtained from the Galilei G2, Pentacam HR, and Sirius 3D in regard to Km, CCT, and ACD can be used interchangeably for clinical applications such as refractive surgery planning, calculation and surgery planning for phakic and pseudophakic intraocular lens, and corneal ectasia follow-up. However, the Bland–Altman analysis for the interdevice agreement of MAE, MPE, and HOA showed significant differences in the 95% LoA (Table 2), suggesting that the data obtained from these measurements from the three different Scheimpflug devices should not be interchanged. Although statistically significant, the differences in MAE may be clinically judged as irrelevant. The 95% LoA for the posterior elevation was wider, especially for the Sirius 3D.

Regarding the variability between Scheimpflug systems, Shankar et al. found that Pentacam software specifically interpolated missing elevation data without warning and that interpolation between samples in the periphery, where space between them is maximum, was the reason for the low repeatability in corneal elevation and HOAs.22 There are no studies regarding these flaws with Sirius 3D or Galilei software, but this could also be the source of the differences in measurements between devices, especially with regard to corneal elevation and HOAs.

One notable limitation of the current study is the use of bilateral eye data. We are aware that measurements obtained from both eyes (right and left) of the same patient are usually correlated, hence the variance between eyes is usually less than that between patients.28 Not considering this correlation while performing the data analysis (ie, using statistical procedures such as t test, analysis of variance, or linear regression that assume that observations are an independent sample of population; none of them used in our study) might lead to an underestimation of standard errors, low P values, and imprecise confidence intervals.29 Some authors attempt to avoid this problem by using data of only one eye and rejecting that from the fellow eye.30 However, this approach also raises other issues, such as rejecting valid data, reducing the potential power of the study, and also ethical considerations (subjecting patients to measurements that were not used in subsequent analysis). Some investigators recommend the use of statistical procedures such as ICC and the Bland–Altman method to determine the relationship between paired measurements from the same patients, as we did in this study.28 Also, we have to consider that a greater sample size would significantly increase the study power and give a higher degree of confidence.

In general, the Galilei G2 Dual Scheimpflug Analyzer, Pentacam HR, and Sirius 3D imaging system showed good to excellent precision for the evaluation of Km values, CCT, anterior chamber depth, anterior and posterior corneal elevation, and HOAs, with a trend toward an augmented difficulty in obtaining repeatability and reproducibility for the last three parameters. To our knowledge, this is the first study to analyze the interdevice interchangeability for Km, CCT, ACD, MAE, MPE, and HOAs with these three Scheimpflug devices; the results suggest that the former three parameters can be used interchangeably but that the latter three parameters should be interpreted cautiously and preferably should not be used interchangeably.

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Bland–Altman plots for mean keratometry values (km) (diopters) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for mean km of (A) the Galilei G2 and (B) Sirius 3D with the Pentacam HR: −0.116 to 0.198 (mean difference: 0.041, P = .151) and −0.280 to −0.003 (mean difference: −0.142, P = .384), respectively.

Figure A. Bland–Altman plots for mean keratometry values (km) (diopters) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for mean km of (A) the Galilei G2 and (B) Sirius 3D with the Pentacam HR: −0.116 to 0.198 (mean difference: 0.041, P = .151) and −0.280 to −0.003 (mean difference: −0.142, P = .384), respectively.

Bland–Altman plots for central corneal thickness (CCT) (µm) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for CCT of the (A) Galilei G2 and (B) Sirius 3D with the Pentacam HR: 13.520 to 17.027 (mean difference: 15.274, P = .435) and −17.402 to −14.956 (mean difference: −16.179, P = .172), respectively.

Figure B. Bland–Altman plots for central corneal thickness (CCT) (µm) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for CCT of the (A) Galilei G2 and (B) Sirius 3D with the Pentacam HR: 13.520 to 17.027 (mean difference: 15.274, P = .435) and −17.402 to −14.956 (mean difference: −16.179, P = .172), respectively.

Bland–Altman plots for aqueous depth (AQD) (mm) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for the AQD of the (A) Galilei G2 and (B) Sirius 3D with the Pentacam HR: −0.009 to 0.027 (mean difference: 0.009, P = .06) and −0.101 to −0.054 (mean difference: −0.078, P = .05), respectively.

Figure C. Bland–Altman plots for aqueous depth (AQD) (mm) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for the AQD of the (A) Galilei G2 and (B) Sirius 3D with the Pentacam HR: −0.009 to 0.027 (mean difference: 0.009, P = .06) and −0.101 to −0.054 (mean difference: −0.078, P = .05), respectively.

Bland–Altman plots for maximum anterior corneal elevation (MAE) (µm) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for anterior corneal elevation of the (A) Galilei G2 and (B) Sirius 3D with the Pentacam HR: 5.830 to 9.090 (mean difference: 7.460, P < .001) and 2.407 to 4.000 (mean difference: 3.203, P < .001), respectively.

Figure D. Bland–Altman plots for maximum anterior corneal elevation (MAE) (µm) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for anterior corneal elevation of the (A) Galilei G2 and (B) Sirius 3D with the Pentacam HR: 5.830 to 9.090 (mean difference: 7.460, P < .001) and 2.407 to 4.000 (mean difference: 3.203, P < .001), respectively.

Bland–Altman plots for maximum posterior corneal elevation (MPE) (µm) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for posterior corneal elevation of the (A) Galilei G2 and (B) Sirius 3D with Pentacam HR: 11.141 to 20.146 (mean difference: 15.643, P < .001) and 4.853 to 8.827 (mean difference: 6.840, P < .001), respectively.

Figure E. Bland–Altman plots for maximum posterior corneal elevation (MPE) (µm) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for posterior corneal elevation of the (A) Galilei G2 and (B) Sirius 3D with Pentacam HR: 11.141 to 20.146 (mean difference: 15.643, P < .001) and 4.853 to 8.827 (mean difference: 6.840, P < .001), respectively.

Bland–Altman plots for total high-order aberrations (HOA) (root mean square) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for total HOA of the (A) Galilei G2 and (B) Sirius 3D with the Pentacam HR: −1.771 to −1.305 (mean difference: −1.538, P < .001) and −1.985 to −1.447 (mean difference: −1.716, P < .001).

Figure F. Bland–Altman plots for total high-order aberrations (HOA) (root mean square) of the Galilei G2 (Ziemer Ophthalmic Systems AG, Port, Switzerland) and Sirius 3D (Costruzione Strumenti Oftalmici, Florence, Italy) with the Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) variables examined in the study; 95% limits of agreement are represented by the solid lines. The 95% limits of agreement for total HOA of the (A) Galilei G2 and (B) Sirius 3D with the Pentacam HR: −1.771 to −1.305 (mean difference: −1.538, P < .001) and −1.985 to −1.447 (mean difference: −1.716, P < .001).

Median and Interquartile Range for the Measurements of Each Examined Variable

ParameterMedian (IQ range: 25 to 75)
Pentacam HRGalilei G2Sirius 3D
Km (D) (range)43.70 (43.30 to 43.95)44.00 (43.50 to 44.20)43.80 (43.30 to 43.90)
CCT (µm) (range)540 (530.70 to 555.50)554.50 (527.00 to 584.50)523.50 (513.70 to 542.96)
MAE (µm) (range)4.00 (3.70 to 4.50)2.00 (1.50 to 3.00)−1.00 (−1.00 to −1.00)
MPE (µm) (range)8.00 (7.00 to 9.00)4.00 (3.00 to 5.00)−2.50 (−3.00 to −2.00)
ACD (mm) (range)3.10 (2.90 to 3.30)3.60 (3.60 to 3.80)3.60 (3.50 to 3.70)
HOA (range)0.35 (0.29 to 0.47)1.82 (1.61 to 2.26)1.60 (1.00 to 2.70)

Interdevice Repeatability, Reproducibility, and Agreement Expressed Through the Bland–Altman Comparison Analysis

ParameterPentacam HRSirius G2Galilei 3D
Km (D)
  CoV (CI)0.157 (0 to 0.161)0.144 (0.100 to 0.196)0.097 (0.066 to 0.143)
  ICC (CI)0.99923 (0.998 to 0.999)0.98798 (0.970 to 1.005)0.993 (0.976 to 1.010)
  95% LoA (mean difference)−0.116 to 0.198 (0.041)−0.280 to −0.003 (0.142)
P.151.384
CCT (µm)
  CoV (CI)0.274 (0.156 to 0.392)0.379 (0.251 to 0.558)0.251 (0.131 to 0.334)
  ICC (CI)0.989 (0.970 to 1.000)0.992 (0.982 to 1.002)0.995 (0.991 to 0.999)
  95% LoA (mean difference)13.520 to 17.027 (15.274)−17.402 to −14.956 (−16.179)
P.435.172
ACD (mm)
  CoV (CI)0.411 (0.319 to .4676)0.289 (0.230 to 0.431)0.039 (0.020 to 0.049)
  ICC (CI)0.982 (0.962 to 1.003)0.996 (0.987 to 1.005)0.644 (0 to 1.344)
  95% LoA (mean difference)−0.009 to 0.027 (0.009)−0.101 to −0.054 (−0.078)
P.061.059
MAE (µm)
  CoV (CI)9.428 (0 to 15.713)00
  ICC (CI)0.927 (0.866 to 0.988)0.968 (0.914 to 1.022)0.941 (0.873 to 1.009)
  95% LoA (mean difference)5.830 to 9.090 (7.460)2.407 to 4.000 (3.203)
P.001.001
MPE (µm)
  CoV (CI)9.428 (7.443 to 12.856)09.428 (0 to 20.203)
  ICC (CI)0.973 (0.953 to 0.993)0.990 (0.978 to 1.002)0.966 (0.935 to 0.997)
  95% LoA (mean difference)11.141 to 20.146 (15.643)4.853 to 8.827 (6.840)
P.001.001
HOA
  CoV (CI)2.772 (2.239 to 3.672)4.329 (2.847 to 5.224)3.267 (2.72 to 3.860)
  ICC (CI)0.758 (0.577 to 0.939)0.984 (0.961 to 1.006)0.995 (0.988 to 1.001)
  95% LoA (mean difference)−1.771 to −1.305 (−1.538)−1.985 to −1.447 (−1.716)
P.001.001

10.3928/1081597X-20140815-02

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