Astigmatism measurements obtained with the Verion Image-Guided System are as reliable as those obtained with the IOLMaster 500/700 and the Pentacam HR/AXL. They can be considered interchangeable.
Abstract
Purpose:
To compare astigmatism and other keratometric parameters obtained with IOLMaster 500/700, Pentacam HR/AXL, and the VERION Image-Guided System.
Setting:
Department of Ophthalmology, Goethe-University, Frankfurt am Main, Germany.
Design:
Retrospective, comparative clinical study.
Methods:
1107 eyes of 654 patients were examined. The outcome parameters analyzed included the horizontal corneal diameter (white-to-white [WTW]), flattest (K1) and steepest keratometry (K2), axis values (K1 and K2 axis), astigmatism, and axis of astigmatism (axis). These parameters were compared between devices using the Bland-Altman method.
Results:
There was no significant difference between the VERION and the IOLMaster 500/700 in corneal astigmatism measurements (P > .05). The astigmatism measurements with the Pentacam HR/AXL showed a statistically significant difference compared with the VERION Image-Guided System. The astigmatism measured with the VERION Image-Guided System was −0.04 ± 0.38 mm smaller (P = .037) when compared with the Pentacam HR and −0.07 ± 0.37 mm smaller (P < .001) than with the Pentacam AXL. The measurements of the astigmatic axis, as well as the K1 axis and the K2 axis showed a high agreement for all devices (P > .05). However, significant differences were found between the devices for the WTW, K1, and K2 measurements (P < .05).
Conclusions:
The astigmatism measured by the VERION Image-Guided System is comparable with the measurements obtained by IOLMaster 500/700 and Pentacam HR/AXL, allowing the devices to be used interchangeably when planning astigmatism correction during cataract and refractive surgery. By limiting the use to measurements in clinic with “green” quality rating, a high agreement for all variables between the VERION Image-Guided System and IOLMaster 500/700 can be achieved.
Recent advances in the correction of corneal astigmatism in the context of cataract and refractive surgery have led to greater independence from spectacles and greater patient satisfaction in visual outcome in recent years.1
The visual outcome of cataract and lens-based surgery depends on accurate keratometric measurements. Correct measurement of corneal astigmatism and astigmatic axis is essential for astigmatism reduction in cataract surgery either by toric lens alignment or by limbal relaxing incisions.2,3 The IOLMaster (Carl Zeiss Meditec AG) is considered the gold standard for ocular biometry in at least most European countries. This is an optical biometer that is based on partial coherence interferometry and measures the anterior curvature of the cornea using auto keratometry, which was first introduced in 2002.4,5 To date, various devices of different techniques have been developed and used, and it is important to ensure a high level of consistency between them to achieve a high standard of quality and satisfactory visual results. Among these devices is the Pentacam (Oculus Optikgeräte GmbH), a noninvasive tomographer based on the Scheimpflug principle.
Various approaches have been developed to improve the marking accuracy of the astigmatic axis on the cornea, which can essentially be divided into manual marking and image-guided marking. Numerous studies have shown that image-based marking is more precise than manual marking.6 The VERION Image-Guided System (Alcon Laboratories, Inc.) is an optical device, which provides a high-resolution, 3D, wide-field imaging of the anterior segment including corneal curvature, iridocorneal angle, and limbal and pupil position and diameter. The system assimilates the preoperative planning phase with the intraoperative direction of the surgeon by creating a digital image of the eye with a marking for toric intraocular lens (IOL) alignment for optimal IOL position during surgery, which is crucial in achieving more accurate refractive results. Previous studies, that compare the Verion Image-Guided System with other devices, had small samples, which might explain the discrepancy of results between studies.7–12 In this study, we evaluated more than 1000 eyes.
The aim of this study was to compare astigmatism and other biometric measurements obtained with the VERION Image-Guided System, Pentacam, and IOLMaster for planning precise toric IOL power calculation and axis alignment during cataract and refractive surgery.
METHODS
This retrospective study included patients, who underwent femtosecond laser-assisted phacoemulsification from November 2014 until April 2017 in the Department of Ophthalmology, Goethe-University, Frankfurt am Main, Germany. Before phacoemulsification with IOL implantation surgery, all participants' eyes received 3 measurements to calculate the IOL power and plan astigmatism correction during femtosecond-assisted lens surgery: the biometer IOL Master 500 or IOL Master 700 (Carl Zeiss Meditec AG), the Scheimpflug-tomographer (Pentacam HR or Pentacam AXL), and VERION Image-Guided System.
This study includes human participants and was approved by the local ethics committee. This study was performed in accordance with the institutional guidelines and the tenets of the Declaration of Helsinki. Before participating in the study, the participants gave their general informed consent. All data generated or analyzed during this study are included in this article. Further enquiries can be directed to the corresponding author.
Inclusion criteria were an age of 18 years and older, wearing of contact lenses at least 2 weeks before the examination, and keratometric measurements of good quality on all 3 devices.
Patients who had previously undergone corneal or refractive surgery, as well as patients with keratoconus—or suspected keratoconus, pellucid marginal degeneration, or pre-existing conditions that could influence corneal biometry, such as previous corneal infections, pterygium, or scars, were excluded from this study. Patients with reduced cooperation or nystagmus were also excluded. Datasets were excluded if the data for one of the parameters were missing or of insufficient quality.
Outcome parameters were the horizontal corneal diameter (white-to-white [WTW]), the flattest (K1) and steepest keratometry (K2) and their axes, the astigmatism, and the axis of astigmatism.
In this study, we examined both eyes in most patients. A possible source of error could be the correlation between both eyes of a person. Therefore, a subgroup analysis was performed in which only 1 eye of each patient was randomly selected.
Devices
The measurements in this study were performed using the 5 devices: Biometer (IOLMaster 500, IOLMaster 700), Scheimpflug-Tomographer (Pentacam HR and Pentacam AXL), and the VERION Image-Guided System. All examinations were performed under low-light conditions.
The IOLMaster is the gold standard of modern optical biometry devices.13 The IOLMaster 500 is based on the principle of partial coherence interferometry for axial length (AL) measurements.14 The device uses infrared laser light with wavelength 780 nm to measure the AL, curvature of the anterior corneal surface, anterior chamber depth (ACD), and the horizontal corneal diameter (WTW). The IOLMaster 500 uses a 6-point telecentric technique for keratometry measurements. For ACD measurements, an image-based slitlamp system is used. However, lens thickness and central corneal thickness cannot be measured by IOLMaster 500.
IOLMaster 700 enables visualization of the complete longitudinal section of the eye and measures AL, ACD, including central corneal thickness and lens thickness. The IOLMaster 700 is based on the principle of swept-source optical coherence tomography. It uses a rapid-cycle, tunable wavelength laser source to sequentially scan the eye. For keratometric readings, the IOLMaster 700 uses a similar 6-point telecentric technique.
The Pentacam HR is a rotating Scheimpflug camera system for anterior segment analysis. It measures the anterior and posterior corneal topography and elevation, total corneal refractive power, corneal power distribution, automatic chamber angle measurement in 360 degrees, chamber depth and volume, WTW, corneal and crystalline lens. The camera rotates about the eye and collects 50 scans in less than 2 seconds to create a 3D image of the anterior segment of the eye. In addition to the anterior segment tomography, the Pentacam AXL allows AL measurement for IOL calculation. The device combines the Scheimpflug principle of the Pentacam HR with a partial coherence interferometry. Like Pentacam HR, the light source is a blue light emitting diode (LED) with a wavelength of 475 nm.15
The VERION (Image-Guided System Software v. 2.6, 2015), first evaluated in clinical trials in 2013, is a technology of the image-guided marking of the astigmatic axis for toric IOL alignment during lens surgery, where the procedure is guided by preoperative or intraoperative high-resolution images of the eye. The device consists of 2 modules: a measurement module and digital marker, which creates a digital image of the eye. The measurement module performs IOL calculations, including astigmatic corrections. The device uses the reflection of concentric light emission diodes within a ring of 2.8 mm diameter to determine the radii and corneal curvature of steep and flat axes, limbal position and diameter, pupil position and diameter, and corneal light reflex position. A digital overlay of the imported preoperative image and live-surgery image was created by using multiple reference points on the conjunctiva and limbus. The images of the eye were transferred from the measurement module to the digital marker and were projected during surgery in the right ocular of the surgeon's microscope and then guide the surgeon in the placement of all corneal incisions and alignment of toric IOLs. The VERION Image-Guided System uses a quality rating system for image quality assessment, in the accuracy of the measurements: The measurements with “green” indicators are more accurate and precise, than the measurements, which are detected as “yellow” and “red.” Pentacam assesses the measurements as “ok” or “not ok.” In our study, the measurements of the VERION Image-Guided System with green and yellow ratings and Pentacam measurements with quality “ok” were included.
Statistical Analysis
Data were extracted from the 5 devices and collected in a password protected Microsoft Office Excel 2010 (Windows, Inc.) spreadsheet file. The statistical analysis was performed using IBM SPSS Statistics v. 21 software (IBM Corp.). The normal distribution was tested using the Shapiro-Wilk test. The results were evaluated using the Bland-Altman method for assessing agreement between 2 clinical methods. The range of agreement in the Bland-Altman plot was defined as the 95% limit for each comparison (mean ± 1.96 SD of the difference). A 2-tailed P value of 0.05 indicated statistical significance. The statistical significance of the interdevice differences in keratometry parameters was evaluated with the 1-sample t test.
For axis analysis, a minimal axis difference value was defined. If the axis difference (Axis1 − Axis2) was higher than 90 degrees, what leads to a high discrepancy of the measurements between the devices, a minimal axis difference (Diff.min) was calculated using the following formula: Diff.min = 180 degrees − (Axis1 − Axis2). For example, an axis difference of 180 degrees was recalculated as 0 degree, 170 degrees as 10 degrees. For sensitivity analysis, a group of Verion Image-Guided System measurements including the best results (only “green” ratings) was defined and was compared with the “yellow” group ratings.
RESULTS
In this study, data from 1107 eyes of 654 patients (47% female) were analyzed and reviewed. The mean age of the patients enrolled in the study was 65.3 ± 11.7 years (range: 18 to 92 years). Mean corneal astigmatism power measured with the VERION Image-Guided System was −1.14 ± 0.91 diopter (D) ranging from 0 to −7.63 D.
Table 1 presents the means of the astigmatism (cylinder) and their axes, WTW, K1 and K2, as well as the standard deviations, minimum, and maximum of all eyes measured with the 5 different devices.
Table 1.
Comparison of the keratometry values and astigmatism obtained from each platform
| Parameter | Verion Mean ± SD (min/max) |
IOL Master 500 Mean ± SD (min/max) |
IOL Master 700 Mean ± SD (min/max) |
Pentacam HR Mean ± SD (min/max) |
Pentacam AXL Mean ± SD (min/max) |
| WTW (mm) | 12.3 ± 0.44 (10.49/14.27) | 11.96 ± 0.39 (10.4/13.5) | 12.04 ± 0.44 (10.7/13.7) | 11.78 ± 0.40 (9.8/12.9) | 11.75 ± 0.44 (10.4/13.0) |
| K1 (mm) | 7.83 ± 0.34 (6.57/9.46) | 7.87 ± 0.30 (7.08/9.05) | 7.89 ± 0.34 (7.04/9.20) | 7.88 ± 0.29 (7.27/9.08) | 7.92 ± 0.33 (7.01/9.17) |
| K1 axis (degrees) | 88.71 ± 65.65 (0/179) | 87.28 ± 65.39 (0/179) | 91.07 ± 62.80 (0/180) | 88.56 ± 69.20 (0/180) | 93.86 ± 66.52 (0/180) |
| K2 (mm) | 7.63 ± 0.33 (6.5/9.08) | 7.67 ± 0.31 (6.89/8.92) | 7.69 ± 0.32 (6.99/9.03) | 7.69 ± 0.30 (6.96/8.92) | 7.72 ± 0.33 (6.96/8.99) |
| K2 axis (degrees) | 89.55 ± 41.90 (0/179) | 90.81 ± 42.61 (0/179) | 86.82 ± 45.87 (0/179) | 89.68 ± 3659 (1.6/176) | 89.87 ± 40.57 (0.4/180) |
| Cylinder (D) | −1.14 ± 0.91 (−7.63/0) | −1.11 ± 0.82 (−6.14/−0.11) | −1.13 ± 0.93 (−7.17/0) | −1.09 ± 0.82 (−6.0/0) | −1.08 ± 0.94 (−6.9/0) |
| Axis (degrees) | 88.72 ± 65.65 (0/179) | 86.97 ± 65.45 (0/179) | 91.05 ± 62.83 (0/180) | 88.57 ± 69.21 (0.1/180) | 93.86 ± 66.52 (0/180) |
K1 = flat keratometry; K2 = steep keratometry; WTW = white-to-white
The mean corneal astigmatism powers measured by VERION Image-Guided System, IOLMaster 500, IOLMaster 700, Pentacam HR, and Pentacam AXL were −1.14 ± 0.91 D, −1.11 ± 0.82 D, −1.13 ± 0.93 D, −1.09 ± 0.82 D, and −1.08 ± 0.94 D, respectively. The VERION Image-Guided System measured the highest mean value of corneal astigmatism, while the Pentacam HR and AXL measured the lowest. However, when looking at the differences in corneal astigmatism between the devices, there was no statistical significance between the VERION Image-Guided System and the IOLMaster 500 (−0.02 ± 0.35 D; P = .182), and between the VERION Image-Guided System and the IOLMaster 700 (−0.02 ± 0.38 D, P = .192). However, there was a significant difference in corneal astigmatism power between VERION Image-Guided System and Pentacam HR (−0.04 ± 0.38 D, P = .037) and VERION Image-Guided System and Pentacam AXL (−0.07 ± 0.37 D, P < .001).
The mean interdevice differences in the corneal astigmatism power, astigmatic axis, K1, K2, as well as K1 axis and K2 axis, and the lower and upper 95% limits of agreement (LoA) with regression for the comparison between the devices are given in Table 2.
Table 2.
Mean interdevice differences, the 95% LoA with R2 value of the keratometry values, and astigmatism
| Parameter | N | Mean difference ± SD | P value | Lower LoA | Upper LoA | R 2 |
| Verion vs IOLMaster 500 | ||||||
| WTW (mm) | 407 | 0.36 ± 0.32 | <.001* | −0.27 | 0.99 | 0.003 |
| K1 (mm) | 486 | −0.04 ± 0.11 | <.001* | −0.27 | 0.18 | 0.043 |
| K1 axis (degrees) | 481 | 2.34 ± 53.00 | .333 | −101.54 | 106.22 | 0.001 |
| K2 (mm) | 483 | −0.04 ± 0.11 | <.001* | −0.25 | 0.17 | 0.023 |
| K2 axis (degrees) | 481 | −0.53 ± 20.22 | .567 | −40.16 | 39.10 | 0.023 |
| Cylinder (D) | 482 | −0.02 ± 0.35 | .182 | −0.71 | 0.67 | 0.006 |
| Axis (degrees) | 482 | −0.39 ± 20.05 | .673 | −39.69 | 38.90 | 0.007 |
| Verion vs IOLMaster 700 | ||||||
| WTW (mm) | 577 | 0.26 ± 0.30 | <.001* | −0.33 | 0.85 | 0.004 |
| K1 (mm) | 621 | −0.07 ± 0.11 | <.001* | −0.89 | −0.45 | 0.006 |
| K1 axis (degrees) | 615 | 0.77 ± 19.65 | .332 | −37.74 | 39.28 | 0.007 |
| K2 (mm) | 615 | −0.06 ± 0.11 | <.001* | −0.16 | 0.28 | 0.009 |
| K2 axis (degrees) | 615 | 1.38 ± 21.16 | .105 | −40.09 | 42.85 | 0.013 |
| Cylinder (D) | 612 | −0.02 ± 0.38 | .192 | −0.76 | 0.72 | 0.007 |
| Axis (degrees) | 615 | 0.37 ± 19.80 | .647 | −38.44 | 39.18 | 0.008 |
| Verion vs Pentacam HR | ||||||
| WTW (mm) | 375 | 0.53 ± 0.28 | <.001* | −0.01 | 1.07 | 0.005 |
| K1 (mm) | 402 | −0.06 ± 0.13 | <.001* | −0.31 | 0.19 | 0.054 |
| K1 axis (degrees) | 402 | −0.25 ± 19.17 | .797 | −37.82 | 37.32 | 0.016 |
| K2 (mm) | 402 | −0.06 ± 0.13 | <.001* | −0.31 | 0.19 | 0.068 |
| K2 axis (degrees) | 402 | 0.56 ± 18.26 | .541 | −35.23 | 36.35 | 0.046 |
| Cylinder (D) | 401 | −0.04 ± 0.38 | .037* | −0.77 | 0.69 | 0.025 |
| Axis (degrees) | 402 | 0.29 ± 17.95 | .747 | −34.89 | 35.47 | 0.013 |
| Verion vs Pentacam AXL | ||||||
| WTW (mm) | 581 | 0.57 ± 0.28 | <.001* | 0.02 | 1.12 | 0.001 |
| K1 (mm) | 650 | −0.08 ± 0.11 | <.001* | −0.29 | 0.14 | 0.013 |
| K1 axis (degrees) | 651 | −0.48 ± 21.36 | .586 | −41.70 | 40.74 | 0.002 |
| K2 (mm) | 651 | −0.09 ± 0.11 | <.001* | −0.30 | 0.12 | 0.003 |
| K2 axis (degrees) | 649 | 1.36 ± 19.27 | .072 | −36.41 | 39.13 | 0.004 |
| Cylinder (D) | 648 | −0.07 ± 0.37 | <.001* | −0.79 | 0.66 | 0.003 |
| Axis (degrees) | 651 | 0.07 ± 21.13 | .935 | −40.71 | 40.85 | 0.002 |
| IOLMaster 500 vs Pentacam HR | ||||||
| WTW (mm) | 307 | 0.19 ± 0.24 | <.001* | −0.28 | 0.66 | 0.015 |
| K1 (mm) | 401 | −0.02 ± 0.09 | <.001* | −0.19 | 0.16 | 0.060 |
| K1 axis (degrees) | 397 | −1.08 ± 20.66 | .299 | −41.57 | 39.41 | 0.027 |
| K2 (mm) | 399 | −0.03 ± 0.09 | <.001* | −0.21 | 0.15 | 0.026 |
| K2 axis (degrees) | 397 | 0.55 ± 21.75 | .618 | −42.08 | 43.18 | 0.079 |
| Cylinder (D) | 397 | −0.03 ± 0.38 | .137 | −0.76 | 0.70 | 0.006 |
| Axis (degrees) | 398 | −0.26 ± 21.19 | .804 | −41.79 | 41.27 | 0.028 |
| IOLMaster 700 vs Pentacam AXL | ||||||
| WTW (mm) | 489 | 0.29 ± 0.25 | <.001* | −0.19 | 0.77 | 0.001 |
| K1 (mm) | 586 | −0.02 ± 0.07 | <.001* | −0.16 | 0.12 | 0.002 |
| K1 axis (degrees) | 581 | −0.06 ± 22.12 | .944 | −43.41 | 43.29 | 0.028 |
| K2 (mm) | 581 | −0.03 ± 0.07 | <.001* | −0.17 | 0.11 | 0.002 |
| K2 axis (degrees) | 579 | −0.48 ± 21.81 | .600 | −43.19 | 42.29 | 0.036 |
| Cylinder (D) | 575 | −0.05 ± 0.42 | .007* | −0.87 | 0.77 | 0.002 |
| Axis (degrees) | 582 | −0.56 ± 21.87 | .539 | −43.43 | 42.30 | 0.024 |
K1 = flat keratometry; K2 = steep keratometry; LoA = limits of agreement; WTW = white-to-white
Statistically significant
To examine differences in corneal astigmatism power and its axis in more detailed, it is also important to consider the measured amount of astigmatism. Differences between the devices depending on the measured astigmatism and the differences of the axes of astigmatism are given in Table 3.
Table 3.
Mean interdevice differences of astigmatism and astigmatic axis in relation to measured amount of astigmatism
| Astigmatism | N | Mean difference ± SD Verion vs IOLMaster 700 |
Mean difference ± SD Verion vs Pentacam HR |
Mean difference ± SD Verion vs Pentacam AXL |
|||
| Cylinder (D) | Axis (degrees) | Cylinder (D) | Axis (degrees) | Cylinder (D) | Axis (degrees) | ||
| 0.0-0.5 D | 239 | 0.12 ± 0.25 | 1.97 ± 31.87 | −0.18 ± 0.39 | 2.58 ± 29.15 | −0.08 ± 0.25 | −0.56 ± 32.76 |
| 0.5-1.0 D | 385 | −0.03 ± 0.36 | 0.5 ± 18.24 | −0.02 ± 0.3 D | −0.4 ± 18.56 | 0.04 ± 0.31 | −1.40 ± 22.07 |
| 1.0-1.5 D | 237 | 0.07 ± 0.37 | 1.05 ± 10.84 | 0.12 ± 0.25 | −0.49 ± 9.96 | 0.11 ± 0.31 | 1.30 ± 8.70 |
| 1.5-2.0 D | 98 | 0.25 ± 0.41 | −0.05 ± 7.49 | 0.16 ± 0.44 | 0.57 ± 6.40 | 0.24 ± 0.34 | 2.24 ± 6.88 |
| 2.0-3.0 D | 98 | 0.19 ± 0.39 | −0.16 ± 4.37 | 0.29 ± 0.50 | −0.29 ± 7.09 | 0.11 ± 0.70 | 1.07 ± 16.33 |
| 3.0-5.0 D | 45 | 0.17 ± 0.24 | 0.93 ± 4.41 | 0.45 ± 0.32 | 0.90 ± 3.5 | 0.21 ± 0.46 | 2.31 ± 6.69 |
In this study, we analyzed the measurement differences of K1 and K2 between the devices. The differences are listed in Table 2. There was a statistically significant difference in the direct comparison of all devices (P < .001 each). The mean difference was less than 0.10 mm in all comparisons, which corresponds to less than 0.5 D.
Looking at the astigmatic axis, as well as the K1 axis and K2 axis, there was no statistically significant difference between the VERION Image-Guided System and the IOLMaster 500 and IOLMaster 700 (P > .05 each). Mean ± SD, P values, and the lower and upper 95% LoA with regression for the comparison between the devices are given in Table 2.
Furthermore, statistically significant differences are observed for WTW readings between all 5 devices (P ≤ .001) as depicted in Table 2.
The comparison of the VERION Image-Guided System measurements with the “green” ratings with the other devices are shown in Table 4. The analysis shows excellent statistical repeatability between the VERION Image-Guided System and the IOLMaster 500 and 700 measurements for all parameters with no significant difference (P > .05), except the WTW value shows a significant difference (P < .001). However, there was a significant difference between the VERION Image-Guided System and the Pentacam HR and Pentacam AXL measurements regarding the WTW, K1, K2, and cylinder measurements (P > .05).
Table 4.
Mean interdevice differences, 95% LoA with regression of the keratometry values, and astigmatism including only Verion traffic light rating system measurements with “green” quality rating
| Parameter | N | Mean difference ± SD | P value | Lower LoA | Upper LoA | R 2 |
| Verion vs IOLMaster 500 | ||||||
| WTW (mm) | 79 | 0.36 ± 0.18 | <.001* | 0.01 | 0.71 | 0.021 |
| K1 (mm) | 91 | 0.004 ± 0.07 | .572 | −0.01 | 0.02 | 0.007 |
| K1 axis (degrees) | 91 | −0.21 ± 17.00 | .907 | −33.53 | 33.11 | 0.016 |
| K2 (mm) | 91 | 0.001 ± 0.07 | .865 | −0.132 | 0.13 | 0.023 |
| K2 axis (degrees) | 91 | −1.97 ± 18.46 | .312 | −38.15 | 34.21 | 0.078 |
| Cylinder (D) | 91 | −0.04 ± 0.33 | .295 | −0.69 | 0.61 | 0.008 |
| Axis (degrees) | 91 | −0.21 ± 17.01 | .907 | −33.55 | 33.13 | 0.016 |
| Verion vs IOLMaster 700 | ||||||
| WTW (mm) | 99 | 0.30 ± 0.25 | <.001* | −0.19 | 0.79 | 0.017 |
| K1 (mm) | 112 | 0.003 ± 0.06 | .507 | −0.11 | 0.12 | 0.033 |
| K1 axis (degrees) | 112 | −0.25 ± 13.19 | .841 | −26.10 | 25.60 | 0.000 |
| K2 (mm) | 112 | −0.01 ± 0.007 | .399 | −0.15 | 0.13 | 0.095 |
| K2 axis (degrees) | 112 | −1.74 ± 13.05 | .161 | −27.32 | 23.84 | 0.003 |
| Cylinder (D) | 111 | −0.05 ± 0.36 | .132 | −0.74 | 0.64 | 0.002 |
| Axis (degrees) | 112 | −1.77 ± 13.08 | .155 | −27.01 | 23.47 | 0.005 |
| Verion vs Pentacam HR | ||||||
| WTW (mm) | 67 | 0.52 ± 0.17 | <.001* | 0.18 | 0.85 | 0.005 |
| K1 (mm) | 77 | −0.02 ± 0.06 | .007 | −0.14 | 0.009 | 0.009 |
| K1 axis (degrees) | 77 | −2.03 ± 19.21 | .357 | −2.74 | −1.32 | 0.001 |
| K2 (mm) | 77 | −0.03 ± 0.08 | .001* | −0.19 | 0.13 | 0.039 |
| K2 axis (degrees) | 77 | 2.66 ± 15.61 | .138 | −27.94 | 33.26 | 0.006 |
| Cylinder (D) | 77 | −0.06 ± 0.28 | .048 | −0.60 | 0.48 | 0.206 |
| Axis (degrees) | 77 | 0.31 ± 16.67 | .871 | −32.36 | 32.98 | 0.016 |
| Verion vs Pentacam AXL | ||||||
| WTW (mm) | 110 | 0.62 ± 0.28 | <.001* | 0.08 | 1.16 | 0.008 |
| K1 (mm) | 118 | −0.02 ± 0.07 | .003* | −0.16 | 0.12 | 0.031 |
| K1 axis (degrees) | 118 | 0.13 ± 13.87 | .917 | −26.64 | 26.89 | 0.002 |
| K2 (mm) | 118 | −0.04 ± 0.07 | <.001* | −0.18 | 0.009 | 0.008 |
| K2 axis (degrees) | 117 | 1.79 ± 12.15 | .114 | −22.02 | 25.60 | 0.009 |
| Cylinder (D) | 117 | −0.88 ± 0.29 | .002* | −0.32 | −1.44 | 0.000 |
| Axis (degrees) | 118 | −0.43 ± 13.82 | .736 | −27.52 | 26.66 | 0.000 |
K1 = flat keratometry; K2 = steep keratometry; LoA = limits of agreement; WTW = white-to-white
Statistically significant
Figure 1 shows the Bland-Altman plots for agreement in the measurement of corneal astigmatism and Figure 2 for the astigmatic axis between the VERION Image-Guided System and the 4 other devices. Low to moderate agreement was found between the devices based on the 95% LoA.
Figure 1.
Bland-Altman plots illustrating the mean difference of the corneal astigmatism power between the VERION system and the IOLMaster 500 (A), IOLMaster 700 (B), Pentacam HR (C), and Pentacam AXL (D), between the IOLMaster500 and the Pentacam HR (E), and IOLMaster 700 and Pentacam AXL (F), as well as the 95% limits of agreement.
Figure 2.
Bland-Altman plots illustrating the mean difference of the astigmatic axis between the VERION system and the IOLMaster 500 (A), IOLMaster 700 (B), Pentacam HR (C), and Pentacam AXL (D), between the IOLMaster500 and the Pentacam HR (E), and IOLMaster 700 and Pentacam AXL (F), as well as the 95% limits of agreement.
A subgroup analysis was performed in which only 1 eye of each patient was randomly selected and included. The results are given in Supplemental Table 1 (available at http://links.lww.com/JRS/B386). There were no substantial differences between the subgroup and the group with all eye.
DISCUSSION
Astigmatism correction during cataract and refractive surgery gives the patients the opportunity to have the best possible quality of vision and reduces dependency on spectacles. Correct measurement of corneal astigmatism and astigmatic axis is an essential condition for patient's satisfaction and the visual outcome.16 Modern devices provide repeatable measurements and provide precise results of keratometry parameters. Previous studies confirmed that the VERION Image-Guided System is equivalent to previously validated devices for keratometric assessment.8,11,17 In this study, the consistency in keratometric measurements of the VERION Image-Guided System was compared with 4 established devices in a large dataset with 1107 eyes.
Our study showed steeper keratometries measured with the VERION Image-Guided System compared with the IOLMaster 500 and 700, as well as Pentacam HR and AXL. For example, the mean flat keratometry (K1) measured with the VERION Image-Guided System was 7.83 mm compared with the Pentacam AXL with 7.92 mm, measuring the flattest value on average. A similar picture emerges for the K2 value, whereby the VERION Image-Guided System also measured the steepest value with an average of 7.63 mm. The highest K2 value was also found with the Pentacam AXL (7.72 mm). Looking at the differences between the 2 mean values of K1 and K2, there is a statistically significant difference between VERION Image-Guided System and all other devices, but without clinical relevance, because the mean difference between all devices was less than 0.10 mm, which corresponds to less than 0.5 D. The tendency of the steeper keratometry measurements is in agreement with the results described in the literature.7,18,19 Fu et al. showed higher K-values measured by the VERION Image-Guided System compared with the IOLMaster and Pentacam, but less steep compared with manual keratometry measured with the YZ38 (Suzhou 66 visual Polytron Technologies, Inc.).18 The authors stated that the image-guided system provides more comparable results with the IOLMaster than with manual keratometry and Pentacam.18 Our results also indicate that the K-values of the VERION Image-Guided System were more comparable with the IOLMaster 500 and 700 as to the Pentacam HR and AXL. Asena et al. also described a similar trend of steeper measured K-values compared with the IOLMaster and auto kerato-refractometer (Topcon KR-8900, Topcon Corp.) and reported that keratometric and astigmatic results obtained from the VERION Image-Guided System and the IOLMaster 500 show an excellent agreement with an intraclass correlation coefficient close to one.7 Labiris et al. analyzed the agreement between the VERION Image-Guided System and the IOLMaster in keratometric values, but also in toric IOL calculation.19 The authors found statistically significantly steeper K-values measured with the VERION Image-Guided System compared with the IOLMaster, albeit with a relatively small difference (≤0.30 D), which led to significantly lower calculated mean IOL powers of the 4 formulas examined.19 They hypothesized that a possible reason for the steeper keratometry values could be the significantly larger diameter of the light reflections on the central cornea (2.3 to 2.5 mm) of the IOLMaster compared with the VERION Image-Guided System, which projects 3 LEDs onto the central 0.8 to 1.2 mm of the cornea to measure the spherical corneal power. Considering the fact that the cornea is steeper in the center, this might explain the significantly steeper K-values measured with the VERION Image-Guided System compared with the IOLMaster.19 Conversely, Mueller and Thomas described flatter keratometry readings with the VERION Image-Guided System compared with the IOLMaster, whereas other authors found no statistically significant differences between the devices.20,21
Although statistically differences in WTW, K1, and K2 were observed between the VERION Image-Guided System and other devices, these did not exceed thresholds generally considered clinically relevant. For most IOL calculations, differences under 0.10 mm or 0.50 D have minimal impact on refractive outcomes. However, in complex situations—especially in cases involving toric lenses, where even small deviations may influence lens selection or axis alignment—surgeons should consider cross-checking with a second device when needed.
Looking at the corneal astigmatism power, there was a high clinical and statistically significant agreement between the VERION Image-Guided System and the IOLMaster 500 and 700, which is currently considered as the gold standard in ocular biometry. The mean difference between the VERION Image-Guided System and the IOLMaster 500 and 700 was only −0.02 ± 0.35 D and −0.02 ± 0.38 D, respectively. Labiris et al. described similar results with good comparability of astigmatism in the vector analysis between the VERION Image-Guided System and the IOLMaster.19 Considering the results between the VERION Image-Guided System and the Pentacam HR and AXL, there was a statistically significant mean difference of −0.04 D and −0.07 D, respectively. Nevertheless, we do not consider the mean differences between the VERION Image-Guided System and the Pentacam HR/AXL to be clinically relevant despite their statistical significance.
Low astigmatism is more common, and obtaining reliable measurements might be even more difficult when a low level of cylinder is present.22
Therefore, it is important to consider the measured amount of astigmatism when analyzing the accuracy of astigmatism measurements. Interestingly, our dataset showed an increase in the mean difference between the VERION Image-Guided System and the IOLMaster 700 in the subanalysis of eyes with an astigmatism of more than 1.5 D. The mean difference was greatest in the subgroup of eyes with 1.5 to 2.0 D, whereas it decreased again slightly in the subgroup of 2.0 to 3.0 D and 3.0 to 5.0 D (0.25 D, 0.19 D, and 0.15 D, respectively). By contrast, there was a continuous increase in the mean difference in corneal astigmatism power when comparing the VERION Image-Guided System with the Pentacam AXL. The greatest agreement between the 2 devices was found in the 1.0 to 1.5 D group with a mean difference of 0.02 D. However, the astigmatic axis in the low astigmatic power range shows greater variability between the devices. One reason for this could be the difficulty in determining the orientation of the steep axis at low astigmatism amounts. The astigmatic axis measurements at high cylinders are more precise, but the difference in cylinder measurements was higher.
Axis analysis of K1 axis, K2 axis, and astigmatism axis showed good comparability between the VERION, IOLMaster, and Pentacam with no statistically significant differences (P > .05 each). The highest mean difference between the devices was 2.34 degrees in the K1 axis when comparing the VERION system with the IOLMaster 500. Lin et al. examined the differences between the VERION Image-Guided System and 4 other devices in corneal keratometric values in 115 eyes and described a difference of 5 to 10.7 degrees with the highest deviation from the kerato-refractometer (KR-8800), whereas Wu et al. found no statistically significant difference in steep axis of astigmatism between VERION Image-Guided System, IOLMaster 700, and Pentacam.23,24
The results of the subgroup analysis indicated that we can increase the accuracy and precision of the measurements by using the traffic light scoring system of the Verion Image-Guided System. By limiting the measurements in the clinic to “green” indicators, a high level of agreement can be achieved for all variables between the Verion Image-Guided System and the IOL Master 500/700. However, the significant difference in cylinder size, K1 and K2 between the Verion Image-Guided System and the Pentacam HR or AXL devices remains, even when only “green” labeled Verion Image-Guided System measurements are included. However, the difference has no clinical relevance.
To the authors' knowledge, there is no study in the literature with a comparable number of eyes that examines the differences between the VERION Image-Guided System, IOLMaster 500/700, and Pentacam HR/AXL.
This study comes with some limitations. The first and most important limitation is the retrospective design. Therefore, no postoperative outcome could be analyzed; thus, further studies are needed here. Another weakness is that both eyes of some patients were included and measured. As this may lead to a possible bias due to a possible correlation of both eyes of a participant, we performed a subgroup analysis where 1 eye per participant was randomly selected and used for the analysis. This underlines the robustness of the analysis.
The Verion Image-Guided System demonstrates in this study strong agreement with established devices such as the IOL Master 500/700 and Pentacam HR/AXL in measuring keratometric and astigmatic parameters. Although minor statistical differences exist—particularly in K1, K2 and cylinder values—these are not clinically relevant in standard cataract and refractive surgery. Given its high precision, especially when using “green” quality indicators, Verion can serve as a reliable tool in preoperative planning. However, in cases requiring maximum accuracy—such as toric IOL, or when dealing with borderline values—it may be advisable to confirm measurements with a second device.
In summary, this study shows that astigmatism and other keratometry parameters, measured by the Verion Image-Guided System is comparable with the measurements obtained by IOL Master 500/700 and Pentacam HR/AXL so that the devices can be interchangeably used to plan astigmatism correction during cataract and refractive surgery.
To ensure a high level of agreement between the devices, we recommend using only measurements labeled green by the traffic light rating system of the Verion Image-Guided System.
WHAT WAS KNOWN
Modern diagnostic devices provide repeatable measurements and provide precise results of keratometry parameters.
WHAT THIS PAPER ADDS
Astigmatism and other keratometry parameters, measured by the Verion Image-Guided System are comparable with the measurements obtained by IOL Master 500/700 and Pentacam HR/AXL.
There is a significant difference in measurements of cylinder between the Verion and Pentacam HR/AXL, but the difference is not clinically relevant.
By limiting to the use of measurements in clinic to the “green” quality rating, a high agreement for all variables between the Verion Image-Guided System and the IOL Master 500/700 can be achieved. Nevertheless, the significant difference in relation to the magnitude of the cylinder, K1, and K2 persists between the Verion Image-Guided System and the Pentacam HR or AXL devices. However, the difference is not clinically relevant.
Footnotes
Disclosures: T. Kohnen: Consultant, Research and Lecturing for Alcon, Oculus, Schwind, Staar. Consultant and Lecturing for Tarsus, Ziemer. Research and Lecturing for Teleon Surgical. Consulting for Abbvie, Geuder, LensGen, Santen, Stadapharm, Thieme, Zeiss Meditec. Lecturing for Allergan, Bausch & Lomb, Johnson & Johnson, MedUpdate, streamedup.K.P. Kaiser: lecture fees from Oculus Optikgeräte GmbH. None of the other authors have any financial or proprietary interest in any material or method mentioned.
First author:
Volha Melianets, MD
Department of Ophthalmology, Goethe-University, Frankfurt am Main, Germany
Contributor Information
Volha Melianets, Email: volha.melianets@gmx.de.
Klemens Paul Kaiser, Email: klemens.kaiser@icloud.com.
Eva Hemkeppler, Email: eva.hemkeppler@ukffm.de.
Myriam Böhm, Email: myriam.boehm@ukffm.de.
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