The recently developed ANTERION (Heidelberg Engineering, Heidelberg, Germany) is a high-resolution swept-source optical coherence tomography (SS-OCT) device that provides a variety of anterior segment metrics, including anterior, posterior, and total corneal curvatures, as well as HOAs with high-resolution, speed, providing an axial length, which calculates the IOL power as well. The high repeatability of anterior segment measurements including HOAs and axial length in ANTERION, has been reported [
16-
18], and the interchangeability in corneal curvature, white-to-white, pupil diameter, and anterior chamber depth between other devices such as IOL Master 700 (Carl Zeiss, Jena, Germany), Pentacam (Oculus, Wetzlar, Germany), and Cassini II (i-Optics, Den Haag, Netherlands) have been studied [
19-
22]. However, there is no comparative study on the HOAs of ANTERION with the Pentacam HR device. Accordingly, the purpose of this study is to confirm the agreement and compatibility of corneal curvature, astigmatism, and corneal HOAs measured by Pentacam HR and ANTERION.
Discussion
In this study, we assessed the agreement of keratometric measurements including power vector analysis of astigmatism in anterior and posterior cornea curvature, TCP, and corneal HOAs obtained by the Scheimpflug camera Pentacam HR and SS-OCT based-device ANTERION. There were statistically significant differences in most values except the anterior Kf, TCP of the flat meridian of cornea, and posterior J0. Most of the keratometric measurements showed poor agreement, which is difficult to use interchangeably. However, J0 and J45 values can be used interchangeable, showing mean differences <0.1 D and narrow ranges of 95% LoA. Among the corneal HOAs, vertical coma, horizontal trefoil, spherical aberration, and each RMS of the fifth and sixth order showed statistically significant differences and the horizontal trefoil and RMS of the fifth and sixth order showed no significant correlation. However, almost all HOAs showed clinically acceptable agreements with a narrow 95% LoA range.
There have been many efforts to reduce residual refractive error after ocular surgery such as cataract or refractive surgery, and this is closely related to the accurate assessment of the ocular biometrics. Recent studies have shown the importance of the considering posterior corneal astigmatism and total keratometry for cataract surgery, as it has been demonstrated to minimize postoperative refractive errors [
4-
9]. The Scheimpflug device has been used to measure both anterior and posterior corneal curvature, and the Pentacam HR showed high accuracy for total corneal astigmatism [
28]. Park et al. [
29] reported that when selecting the appropriate toric IOL cylinder power, vector summation using the anterior and posterior corneal curvature measured by Pentacam HR showed decreased prediction error for astigmatism, and was superior to IOL Master keratometry and simulated keratometry from Pentacam HR. As such, since the clinical usefulness of Pentacam HR for keratometry and utilization has already been proven, it is important to evaluate compatibility with Pentacam HR for other newly developed devices.
In other studies of inter-device comparison for keratometry, Ozyol et al. [
30] assessed the agreement between Pentacam HR and IOL Master 700 in 62 eyes of 62 patients. When comparing the mean keratometry (Km) of the IOL Master 700 of the 2.5-mm zone with that of the Pentacam HR at the 2- and 3-mm zone, there was a statistically significant difference between the two devices (
p < 0.001), and the 95% LoA ranged from −0.45 to 0.17 D in the 2-mm zone and −0.38 to −0.02 D in the 3-mm zone. These differences are sufficient to cause refractive errors when calculating the IOL power. However, there were agreements on the J0 and J45 vectoral components of astigmatism of simulated keratometry, showing that the mean difference was 0.07 ± 0.09 D with a 95% LoA of −0.10 to 0.24 for J0 and −0.016 ± 0.15 D with a 95% LoA of −0.31 to 0.27 for J45. Cui et al. [
31] compared keratometric measurements using the Pentacam HR and Cassini in 117 eyes of 117 patients before cataract surgery. The statistically significant differences were observed in Km, astigmatism, and J0 for the anterior cornea and in Kf, Km, astigmatism, and J0 for the posterior cornea. In addition, the ranges of 95% LoA were large for most variables not to be used interchangeably, extending beyond 0.5D in most of the variables. Tana-Rivero et al. [
22] compared the ocular biometry of 49 eyes using ANTERION, IOL Master 700, and Pentacam AXL (Oculus) and reported no statistically significant difference for anterior Ks and Kf. For the agreement between ANTERION and Pentacam AXL, the 95% LoA range was wide (from −0.3643 to 0.5069 D for Kf and from −0.3705 to 0.5638 D for Ks). Pan et al. [
32] assessed the agreement of ray-traced TCP using a Pentacam, Sirius Scheimpflug-Placido topographer (CSO, Firenze, Italy), and Galilei dual Scheimpflug analyzer (Ziemer, Port, Switzerland) in 74 eyes of 74 healthy subjects. They reported that the single Scheimpflug camera, Pentacam, and Sirius, showed an almost identical result in TCP with a 95% LoA of −0.45 to 0.51 D, which is clinically acceptable. Nonetheless, the dual Scheimpflug camera showed a higher value, and they said the difference in principle (single or dual Scheimpflug) of the devices contributed to this difference in results. Savini et al. [
33] compared anterior segment values using the AS-OCT device MS-39 (CSO, Florence, Italy) and Pentacam HR and Sirius. The results showed that MS-39 cannot be considered interchangeable due to moderate agreement. Sel et al. [
34] compared Pentacam AXL and IOL Master 700 in 50 eyes, and concluded that J0 and J45 values are interchangeable with mean difference of 0.02 ± 0.11 for J0 (
p = 0.115), 0.02 ± 0.10 (
p = 0.255) with narrow 95% LoA; −0.18 to 0.23 for J0, −0.18 to 0.21 for J45. However, Km, anterior chamber depth, and AXL are not interchangeable between two devices. In line with previous studies, the keratometric values were not interchangeable, showing a wide range of 95% LoA in anterior K (0.68 to 0.80 D), posterior K (0.25 to 0.31 D), and TCP (0.79 to 1.10 D) in this study. However, vectoral components were interchangeable, showing a narrow range of 95% LoA in anterior J0 (−0.27 to 0.13), anterior J45 (−0.29 to 0.10), posterior J0 (−0.07 to 0.08), posterior J45 (−0.07 to 0.12), TCP J0 (−0.32 to 0.11), and TCP J45 (−0.28 to 0.09).
Regarding corneal HOAs, previous studies have reported the results of comparing HOAs measured by different devices. Piccinini et al. [
35] compared the HOAs using the Pentacam HR and Galilei G4, which were based on a dual Scheimpflug camera with a placido system in 105 eyes of 105 subjects. Total RMS, coma, and trefoil showed significant difference (
p < 0.001) but not in spherical aberration (
p = 0.125). The mean differences (95% LoA range) were −0.0034 ± 0.101 μm (−0.233 to 0.166) for the oblique trefoil, 0.052 ± 0.103 μm (−0.150 to 0.254) for the horizontal trefoil, 0.152 ± 0.141 μm (−0.125 to 0.427) for the horizontal coma, −0.055 ± 0.139 μm (−0.328 to 0.217) for the vertical coma, and 0.012 ± 0.081 μm (−0.159 to 0.159) for the spherical aberration, and 1.238 ± 0.677 μm (−0.536 to 1.081) for the total RMS, showing reasonable correlations and narrow 95% LoA between two devices, all of which suggest these measurements can be considered equivalent for a clinical setting. Kim et al. [
36] compared the measurement of 45 eyes using a color LED topographer Cassini, and Pentacam HR. Among the measurements, spherical aberration, coma, trefoil, tetrafoil, and astigmatism of anterior, posterior and total keratometry did not differ between the two devices, but there were significant differences in the mean of anterior and total keratometry and the axis of astigmatism of anterior cornea curvature. In the agreement analysis, total corneal astigmatism and vector component J0, J45 showed a low degree of agreement (95% LoA: −0.845 to 1.125 D for astigmatism, −2.415 to 2.235 D for J0, −1.389 to 0.989 D for J45). Shin et al. [
37] compared corneal curvature and HOAs using a Placid-based videokeratoscope Keratron scout (Optikon, Rome, Italy) and Pentacam HR in 46 eyes of 23 patients. They reported that there was no statistically significant difference for the anterior Ks, Kf, and Km and total RMS, corneal spherical aberration, but not in the coma of a total cornea (
p = 0.005), and the trefoil of an anterior and total cornea (
p < 0.001). In the present study, vertical coma, horizontal trefoil, spherical aberration, and each RMS of the fifth and sixth order showed a statistically significant difference. Nevertheless, there were moderate or higher correlations and an acceptable 95% LoA range in all HOAs except the horizontal trefoil and RMS of the fifth order and RMS of sixth order. The values of HOAs decreased as the order of the Zernike coefficient increased as others have shown [
38]. Especially in ANTEIRION, the RMS of the fifth and sixth order HOAs showed up as zero in many cases. This may affect the wide range of the 95% LoA in RMS of the fifth and sixth order HOAs in this study.
In this study, the two devices were interchangeable in some, but not interchangeable in others. Since both devices are expensive, it is not common to have both devices in one clinic. And ophthalmologists are often faced with the task of interpreting results that have been tested in other clinics against the results of their own instruments. Thus, it is necessary to compare and investigate the interchangeability of results of two different devices in a clinical setting. Considering the cause of the difference in corneal measurements between two devices, the most likely cause is the difference in measurement principles. Above all, there is a difference in light source between Scheimpflug camera, which obtains an image of anterior segment by emitting a blue LED with a wavelength of 450 nm, and OCT-based technology using light with a wavelength of 1,300 nm. ANTERION take a shorter time for image acquisition than Pentacam HR, which may be less chance of giving irritation to the subjects. In addition, ANTERION applies an eye-tracking technology during all measurements. These differences may affect the differences in results of the two devices in the present study.
This study has a few limitations. First, the number of subjects was relatively small, and adults aged only 20 to 60 were included. Second, since the measurement was not repeatedly performed for each device, the measurement error for the value itself cannot be excluded. However, both devices have shown good repeatability in other previous studies [
16,
33,
39]. Also, image quality is always checked during image acquisition. In addition, all the participants in this study were well cooperated with no underlying medical/ophthalmological history and fully understood the examination method, so examinations proceeded easily with an experienced examiner. Thus, it is thought that the measurement error would have been small. Third, comparisons were not made according to the degree of refractive error, which can affect HOAs [
38]. Fourth, patients who had corneal diseases such as keratoconus or underwent corneal refractive surgery were not evaluated. Further studies with patients of various age groups, refractive errors, and corneal conditions would be necessary. In addition, as there are more devices based on various principles, it is necessary to use them to compare anterior segment measurements together.
In conclusion, our study is the first to compare the keratometry, including TCP and HOAs, between ANTERION and Pentacam HR. Our results showed that there are statistically significant differences in keratometic measurement not acceptable for interchangeable use. However, HOAs showed acceptable agreement, except for horizontal trefoil and RMS of the fifth and sixth order.