Comparison of Ocular Biometry Measurements from Two Swept-Source OCT Devices: Eyestar 900 vs. Anterion

Abstract

Background Advanced swept-source optical coherence tomography (SS-OCT) devices are the current gold standard for the measurement of ocular biometric and keratometric parameters, which are essential for the calculation and selection of intraocular lenses (IOLs). This study compares the agreement of two SS-OCT devices, the Eyestar 900 (Haag-Streit, Köniz, Switzerland) and the Anterion (Heidelberg Engineering, Heidelberg, Germany).

Materials and Methods All patients undergoing cataract surgery or seeking consultation for corneal abnormalities between January 2024 and May 2024 were eligible for inclusion. Both eyes were included in the final analysis.

Results A sample of 86 eyes from 43 patients was analysed. The mean differences (ES-AN) across all data between the Eyestar 900 (ES) and Anterion (AN) were as follows: anterior chamber depth (ACD) − 0.080 mm (ICC > 0.926), axial length (AL) 0.015 mm (ICC > 0.99), central corneal thickness (CCT) 0.914 µm (ICC > 0.921), corneal curvature along the flat meridian (K1) − 0.024 D (ICC > 0.904), and steep meridian (K2) − 0.210 D (ICC > 0.902), white-to-white corneal diameter (WTW) 0.215 mm (ICC > 0.81). There was excellent agreement for ACD, AL, CCT, K1, K2, and WTW. However, the corneal axis (AX) showed only moderate agreement (ICC > 0.389), with a mean difference of 5.97° and a notable standard deviation of 58.6°.

Conclusions The Eyestar 900 and Anterion demonstrated substantial agreement for all parameters except for the corneal meridian axis. It may be assumed that the inclusion of eyes with irregular corneal topographies may have contributed to this discrepancy.

Summary Overall, there was a high level of agreement between the Eyestar 900 and Anterion. It is reasonable to assume that the measurement outcomes provided by both devices are interchangeable for the calculation of target refractive outcomes for intraocular lenses, with no clinically relevant differences.

Zusammenfassung

Hintergrund Moderne optische Swept-Source-Kohärenztomografen (SS-OCT) repräsentieren derzeit den Goldstandard für die Messung biometrischer und keratometrischer Parameter des Auges, die für die Berechnung und Auswahl von Intraokularlinsen (IOL) unerlässlich sind. Im Rahmen dieser Studie erfolgt ein Vergleich der Übereinstimmung zweier SS-OCT-Geräte, nämlich des Eyestar 900 (Haag-Streit, Schweiz) und des Anterion (Heidelberg Engineering, Deutschland).

Ergebnisse. Die vorliegende Studie umfasste die Analyse von insgesamt 86 Augen von 43 Patienten. Die mittleren Unterschiede (ES-AN) der biometrischen Parameter zwischen Eyestar 900 (ES) und Anterion (AN) lassen sich wie folgt zusammenfassen: Vorderkammertiefe (ACD) − 0,080 mm (ICC > 0,926), Achsenlänge (AL) 0,015 mm (ICC > 0,99), zentrale Hornhautdicke (CCT) 0,914 µm (ICC > 0.921), Hornhautkrümmung entlang des flachen Meridians (K1) − 0,024 D (ICC > 0,904) und des steilen Meridians (K2) − 0,210 D (ICC > 0,902), Weiß-zu-Weiß-Hornhautdurchmesser (WTW) 0,215 mm (ICC > 0,81). Es bestand eine ausgezeichnete Übereinstimmung für ACD, AL, CCT, K1, K2 und WTW. Die Hornhautachse (AX) zeigte jedoch nur eine mäßige Übereinstimmung (ICC > 0.389), mit einer mittleren Differenz von 5,97° und einer beachtlichen Standardabweichung von 58,6°.

Schlussfolgerungen Die Ergebnisse der Untersuchung des Eyestar 900 und des Anterion wiesen für alle Parameter eine hohe Übereinstimmung auf, mit Ausnahme der Meridianachse der Hornhaut. Es kann angenommen werden, dass die Einbeziehung von Augen mit unregelmäßigen Hornhauttopografien zu dieser Diskrepanz beigetragen haben könnte.

Zusammenfassung Im Rahmen der durchgeführten Untersuchung konnte ein hohes Maß an Übereinstimmung zwischen dem Eyestar 900 und dem Anterion festgestellt werden. Es lässt sich folgern, dass die von beiden Geräten gelieferten Messergebnisse für die Berechnung der refraktiven Zielwerte für Intraokularlinsen austauschbar sind und keine klinisch relevanten Unterschiede bestehen.

Keywords

OCT Eyestar - Anterion - swept source (SS) OCT - ocular biometry

Schlüsselwörter

Eyestar - Anterion - Augenbiometrie - Swept Source (SS)

Background

Although the prediction of refractive outcomes after cataract surgery has consistently improved over time, the most accurate formula for these predictions remains a subject of ongoing debate among researchers and practitioners in the field [1]. The foundation for calculations made using these formulas is the precise measurement of ocular biometric data, the quality of which directly impacts postoperative refractive outcomes.

Eyestar 900 (ES) and Anterion (AN) are two advanced swept-source optical coherence tomography (SS-OCT) devices designed to provide high-resolution imaging and accurate biometric data.

This retrospective analysis of study data compares their agreement in measuring key ocular parameters, including anterior chamber depth (ACD), axial length (AL), central corneal thickness (CCT), corneal curvature along the flat (K1) and steep (K2) meridians, steep meridian axis (AX), and white-to-white corneal diameter (WTW). This evaluation will help to determine their reliability and potential clinical implications.

Materials and Methods

This study aimed to evaluate the agreement between two SS-OCT devices, the Eyestar 900 (Haag-Streit, Köniz, Switzerland) and the Anterion (Heidelberg Engineering, Heidelberg, Germany), in measuring key ocular parameters of the anterior and posterior segments.

The study involved human participants who provided written informed consent prior to inclusion. The study was reviewed by the appropriate ethics committee and conformed to the tenets of the Declaration of Helsinki, Good Clinical Practice, ISO 14 155, as well as all applicable Swiss legal regulations.

Population

Participants were recruited from a secondary referral centre, with inclusion criteria encompassing individuals of legal age, irrespective of sex, ethnicity, or corneal status. Individuals from vulnerable populations, those unable to provide consent, those unable to maintain fixation during the examination, individuals with active ocular inflammation or infection, and those with a tear film break-up time of less than 5 seconds were excluded.

The study included participants with diverse corneal and endothelial irregularities, such as keratoconus, or with a history of corneal allogenic intrastromal ring segments (CAIRS), Descemetʼs membrane endothelial keratoplasty (DMEK), laser-assisted in situ keratomileusis (LASIK), or radial keratotomy (RK), as well as those with lenticular irregularities, including patients with cataracts or intraocular lenses (IOLs).

Study procedure

To ensure that the study equipment was at operating temperature, it was powered on at least 30 minutes ahead of the scheduled data collection. All measurements were conducted in a single session under identical conditions after informed consent was obtained. Participants were first measured on the Anterion and then alternated between devices until three measurements per eye were taken on each device, the order of which was not randomised. The data from the three measurements were averaged for each parameter in each eye of each participant.

All measurements were performed by trained operators. In cases where the initial measurement failed to meet the deviceʼs quality control algorithm, the procedure was repeated once. If the device provided a numerical value, it was included in the analysis. No follow-up visits were conducted.

Statistical analysis

To evaluate the agreement between the Eyestar 900 and Anterion, we used Bland-Altman analysis with 95% limits of agreement (LoA) and calculated the intraclass correlation coefficient (ICC) [2]. The statistical analysis focused on identifying systematic differences and the degree of correlation between the measurements from the two devices.

To address potential intra-subject biases, it is standard practice to include only one eye per participant in statistical analyses involving ocular data due to the natural correlation between eyes. In our study, we have included both eyes (OU) as they differed significantly in status–for example, one eye being preoperative and the other postoperative–as this introduces substantial differences between them. Recognising that some degree of intra-subject correlation still exists, we compared the right (OD) and left (OS) eyes for each parameter on the Eyestar data to gain an understanding of how the eye status affects correlation.

Calculations were performed in RStudio 2023.12.1 Build 402 (Posit Software, PBC, Boston, MA, USA) using the packages BlandAltmanLeh, ggplot2, and irr.

Results

A total of 86 eyes from 43 patients were included in the analysis. The participants can be classified into two groups based on their history of cataract surgery: those who had not undergone cataract surgery (phakic) and those who had received surgical treatment for cataracts (pseudophakic). [Table 1] summarises the basic characteristics of these two groups of interest.

Table 1 Basic characteristics of study population.

Characteristic	Phakic	Pseudophakic	Total
N eyes (participants)	64 (26)	22 (17)	86 (43)
Mean age ± SD [years]	61.6 ± 14.8	62.6 ± 11.7	61.0 ± 15.3
Age range [years]	23 – 85	36 – 78	23 – 85

Across the sample, 20 participants presented with corneal irregularities, amongst which there were 3 CAIRS, 5 keratoplasties (DMEK/DSAEK/PKP), 4 LASIK, 1 RE-PRK LASEK, 1 Fuchsʼ dystrophy, and 1 RK. Additionally, 20 participants presented with preoperative cataracts of varying degrees. Finally, 3 participants had no cornea or lens status that was notable in the context of this study. Due to the limited number of observations for each corneal condition, it was not feasible to conduct subgroup analyses.

[Table 2] presents the mean for each parameter, accompanied by the standard deviation and number of observations (n). In conducting these calculations, all values exported by the devices were included, irrespective of the outcome of the deviceʼs quality control algorithm. For the listed parameters, where the number of observations (n) was less than 86, the respective device did not return a value for a number of participants (86 – n).

Table 2 Means and mean differences of biometric parameters.

Parameter [unit]	Eyestar 900 OU Mean ± SD (n)	Anterion OU Mean ± SD (n)	Mean Difference (ICC)
ACD [mm]	3.4 ± 0.6 (71)	3.6 ± 0.8 (85)	0.080 (> 0.926)
AL [mm]	23.8 ± 1.3 (79)	23.8 ± 1.3 (83)	0.015 (> 0.990)
CCT [µm]	546.9 ± 42.6 (82)	543.8 ± 46.7 (86)	0.914 (> 0.921)
Flat K(1) [D]	42.9 ± 1.7 (83)	42.8 ± 3.1 (86)	− 0.024 (> 0.904)
Steep K(2) [D]	43.9 ± 1.9 (83)	44.2 ± 2.6 (86)	− 0.210 (> 0.902)
WTW [mm]	12.1 ± 0.4 (85)	11.8 ± 0.4 (85)	0.215 (> 0.810)
Steep axis [°]	102.5 ± 54.5 (83)	95.7 ± 45.1 (86)	5.968 (< 0.732)

The mean differences between the ES and the AN (ES-AN) are presented in [Table 2] along with the calculated ICC. Excellent agreement was observed for ACD, AL, CCT, K1, K2, and WTW ([Fig. 1]  a–f).

Fig. 1 Anterior chamber depth (ACD), axial length (AL), central corneal thickness (CCT), corneal curvature along the flat (K1) and steep (K2) meridians, and white-to-white corneal diameter (WTW).

However, the corneal axis only exhibited moderate agreement (ICC < 0.732), with a mean difference of 5.97° and a notable standard deviation of 58.6°. [Fig. 2] displays the Bland-Altman plot for the AX measurement.

Fig. 2 Axis of the steep meridian (AX).

To estimate the level of correlation between both eyes of a participant, the ICC was calculated for all parameters between OD and OS of the ES as shown in [Table 3].

Table 3 Mean differences and ICC of biometric parameters between OD and OS measured on the Eyestar 900.

Parameter [unit]	Mean Difference |OD-OS|	ICC
ACD [mm]	0.31 ± 0.56	0.068 < ICC < 0.672
AL [mm]	0.24 ± 0.34	0.928 < ICC < 0.979
CCT [µm]	19.95 ± 31.63	0.365 < ICC < 0.771
Flat K(1) [D]	0.55 ± 0.60	0.793 < ICC < 0.938
Steep K(2) [D]	0.59 ± 0.52	0.814 < ICC < 0.944
WTW [mm]	0.10 ± 0.10	0.874 < ICC < 0.967
Steep axis [°]	38.32 ± 41.48	0.212 < ICC < 0.573

There is excellent agreement between OD and OS for AL, good agreement for WTW and K2, moderate agreement for K1, and poor agreement for CCT, AX, and ACD.

Discussion

A notable limitation of this study is the heterogeneity of the study population. A diverse range of patients was included, encompassing those with various corneal irregularities and both phakic and pseudophakic eyes. This approach was taken to reflect the wide spectrum of patients who may present for IOL implantation and to understand the performance of the devices across a broad clinical scenario. While this heterogeneity may have introduced additional variability, it reflects the diverse patient population encountered in clinical settings.

Despite this limitation, our findings are consistent with those reported by Lender et al. [3] and Sorkin et al. [4], both of whom found good agreement between the ES and the AN. Lender et al.ʼs study included cataract surgery candidates over the age of 40 undergoing standard biometric measurements prior to surgery, excluding participants whose ocular measurements had a standard deviation exceeding 0.05 mm or D, and stratified participants based on astigmatism levels using a cutoff of 1.00 D. In contrast, Sorkin et al. collected data from the medical records of patients older than 18 years who underwent evaluation for cataract surgery and excluded patients with prior cataract surgery or significant corneal irregularities, whereas our study intentionally included such cases.

In our study, the ES and AN demonstrated substantial agreement for all parameters except for the axis of the corneal meridian (AX). A mean difference of 5.97° suggests that the devices provide similar results on average; however, the large standard deviation indicates significant variability. The ICC reflects the consistency or reliability of the measurements; here, a moderate ICC value indicates a fair degree of agreement between the two methods, though not perfect. The combination of a moderate ICC and high variability raises questions about the interchangeability of these devices, at least for this parameter. A potential explanation for this discrepancy could be the relatively small sample size combined with the inclusion of patients from different subgroups, which may have increased measurement variability. The lack of subgroup analyses likely prevented us from identifying specific factors contributing to this variability and the inclusion of eyes with corneal irregularities could have contributed to the discrepancies observed between the devices, limiting the generalisability of our findings. Though generally, the axis is poorly defined in eyes with low astigmatism (|K2-K1|), and for an astigmatism of 0 D, the axis is arbitrary, making differences in corneal axis significant only for higher levels of astigmatism.

Interestingly, despite their exclusion criteria and stratification based on astigmatism, Lender et al. [3] also identified weak correlations in AX measurements between devices, similar to our findings. Future studies with larger, more homogeneous subgroups are needed to elucidate the performance of these devices in specific patient populations. Enhancing the accuracy of AX measurements is crucial for the successful implantation of toric lenses, and ongoing development in this area is needed.

As shown in [Table 2], the AN exhibited a higher success rate for measurements, as evidenced by the number of observations for each parameter, whereas the ES data exhibited less deviation when analysed in terms of standard deviation. This finding contrasts with that reported by Sorkin et al. [4]. This discrepancy might be attributed to the different confidence thresholds of the devices for the data obtained. Similar to the study by Sorkin et al., our analysis of unsuccessful measurements revealed no distinctive characteristics or comorbidities.

Overall, we observed a high level of concordance between the two devices, consistent with results reported in the literature. Moreover, other studies have found positive correlations between the ES and various ocular biometry devices [5], [6], [7], [8], [9], further supporting its reliability across different clinical settings.

Supplements

Tables for averaged AN and ES data:

• Eyestar_Averaged_Data.csv

• Anterion_Averaged_Data.csv

Conflict of Interest

J. V. K. L. and T. J. are employees of Haag-Streit AG. D. G. has received lecture fees. C. T., D. K., E. V., P. S. declare that they have no conflict of interest.

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Publication History

Received: 06 October 2024

Accepted: 29 October 2024

Article published online:
10 December 2024