Journal of Refractive Surgery

Original Article Supplemental Data

Agreement Between Angle-to-Angle Distance and Aqueous Depth Obtained With Two Different Optical Coherence Tomographers and a Scheimpflug Camera

Pedro Tañá-Rivero, MD, PhD; María Dolores Rodríguez-Carrillo, MD; María Ruíz-Santos, MD; Berta García-Tomás, MD; Robert Montés-Micó, PhD

Abstract

PURPOSE:

To compare angle-to-angle (ATA) distance and aqueous depth (AQD) readings produced by two different optical coherence tomography (OCT) devices and a Scheimpflug camera.

METHODS:

ATA distance and AQD were measured in 60 eyes using the Visante time-domain OCT (TD-OCT) (Carl Zeiss Meditec AG), the Anterion swept-source OCT (SS-OCT) (Heidelberg Engineering GmbH), and the Pentacam HR Scheimpflug camera (Oculus Optikgeräte GmbH). Moreover, ATA distance was measured along the horizontal and vertical meridians. Bland-Altman analysis was used to assess the agreement between devices.

RESULTS:

All three devices did not yield similar horizontal ATA distance: 11.96 ± 0.47 mm (TD-OCT), 11.96 ± 0.42 mm (SS-OCT), and 11.05 ± 0.52 mm (Pentacam). More specifically, the Pentacam yielded significantly smaller values (approximately 0.9 mm, P < .001). Mean vertical ATA distance was 12.61 ± 0.65 and 12 ± 0.65 mm for the TD-OCT and SS-OCT, respectively (P = .983). Vertical ATA distance was significantly larger than horizontal ATA distance for both OCT devices (approximately 0.6 mm, P < .001). The lowest mean difference was found between both OCT devices (0.0068 and −0.0415 mm, for horizontal and vertical meridians, respectively) and the highest between the Pentacam and the two OCT devices (approximately 0.9 mm). As for AQD, inter-device mean values were also statistically significant: 2.89 ± 0.48, 2.82 ± 0.49, and 2.79 ± 0.50 mm, for the TD-OCT, SS-OCT, and Pentacam, respectively (P < .001). Mean differences were similar for the TD-OCT versus SS-OCT and SS-OCT versus Pentacam (approximately 0.02 mm), and larger between the TD-OCT and Pentacam (approximately 0.05 mm).

CONCLUSIONS:

The results show that the TD-OCT and SS-OCT are interchangeable instruments for ATA distance measurement but the Pentacam is not with either of the two OCT devices. A clinical criterion should assess whether these three devices could be used interchangeably for AQD measurement.

[J Refract Surg. 2021;37(2):133–140.]

Abstract

PURPOSE:

To compare angle-to-angle (ATA) distance and aqueous depth (AQD) readings produced by two different optical coherence tomography (OCT) devices and a Scheimpflug camera.

METHODS:

ATA distance and AQD were measured in 60 eyes using the Visante time-domain OCT (TD-OCT) (Carl Zeiss Meditec AG), the Anterion swept-source OCT (SS-OCT) (Heidelberg Engineering GmbH), and the Pentacam HR Scheimpflug camera (Oculus Optikgeräte GmbH). Moreover, ATA distance was measured along the horizontal and vertical meridians. Bland-Altman analysis was used to assess the agreement between devices.

RESULTS:

All three devices did not yield similar horizontal ATA distance: 11.96 ± 0.47 mm (TD-OCT), 11.96 ± 0.42 mm (SS-OCT), and 11.05 ± 0.52 mm (Pentacam). More specifically, the Pentacam yielded significantly smaller values (approximately 0.9 mm, P < .001). Mean vertical ATA distance was 12.61 ± 0.65 and 12 ± 0.65 mm for the TD-OCT and SS-OCT, respectively (P = .983). Vertical ATA distance was significantly larger than horizontal ATA distance for both OCT devices (approximately 0.6 mm, P < .001). The lowest mean difference was found between both OCT devices (0.0068 and −0.0415 mm, for horizontal and vertical meridians, respectively) and the highest between the Pentacam and the two OCT devices (approximately 0.9 mm). As for AQD, inter-device mean values were also statistically significant: 2.89 ± 0.48, 2.82 ± 0.49, and 2.79 ± 0.50 mm, for the TD-OCT, SS-OCT, and Pentacam, respectively (P < .001). Mean differences were similar for the TD-OCT versus SS-OCT and SS-OCT versus Pentacam (approximately 0.02 mm), and larger between the TD-OCT and Pentacam (approximately 0.05 mm).

CONCLUSIONS:

The results show that the TD-OCT and SS-OCT are interchangeable instruments for ATA distance measurement but the Pentacam is not with either of the two OCT devices. A clinical criterion should assess whether these three devices could be used interchangeably for AQD measurement.

[J Refract Surg. 2021;37(2):133–140.]

The measurement of anterior segment distances is extremely important for clinical diagnosis and for refractive surgery procedures. Specifically, knowing the anterior chamber dimension is mandatory when a phakic intraocular lens (IOL) is to be implanted for refractive error correction in myopic, hyperopic, and/or astigmatic eyes. An adequate IOL size is required to prevent undesired adverse events such as decentration, rotation, or inappropriate vaulting.1,2 Corneal diameter is frequently used to calculate the phakic lens size. This parameter can be easily measured using devices such as a ruler, an optical biometer, or a corneal topographer. However, discrepancies across studies and the difficulty in accurately determining the exact location where the cornea ends and the sclera begins has tipped the scales in favor of internal instead of external distances.3 In this sense, it would be more appropriate to measure parameters such as the angle-to-angle (ATA) distance, which requires measuring devices that are different from those used for corneal diameter measurement (eg, anterior segment optical coherence tomography [OCT] or a Scheimpflug camera). The aqueous depth (AQD) is another relevant distance that should be measured when a phakic lens is considered.

It is well known that OCT is a non-invasive technique that produces reliable and objective images of different anterior chamber structures.4 This technology has improved substantially, from the first instruments, which were time-domain (TD)–based, to the newest state-of-the-art ones, which are spectral-domain–based and rely on swept-source (SS) technology.5 The SS-OCT devices that are on the market use long-wavelength light sources and have a faster scanning speed, higher resolution, and automated measurement of different parameters compared to the initial TD models.5 SS-OCT provides better performance in detecting deeper angle structures.6 Scheimpflug photography has also been used to measure some anterior segment parameters, although significant differences between devices have been reported.7–9 New instruments available on the market must provide measurements in agreement with previous well-established technology that measures the same parameter.

In this context, the purpose of the current study was to evaluate the agreement of two anterior segment OCT devices and one Scheimpflug camera: the Anterion SS-OCT (Heidelberg Engineering GmbH), the Visante TD-OCT (Carl Zeiss Meditec AG), and the Pentacam HR Scheimpflug camera (Oculus Optikgeräte GmbH). To our knowledge, no studies to date have assessed the agreement of these three instruments that are so widely used in clinical practice. Hence, this study aimed to find out whether they could be used interchangeably in clinical practice for the measurement of ATA distance and AQD.

Patients and Methods

In this prospective observational study, 60 patients were consecutively recruited. The Oftalvist Review Board approved the study, which was conducted in accordance with the tenets of the Declaration of Helsinki. Exclusion criteria were the presence of any ocular disease or a poor fixation. Prior to any measurements, the patient's refraction and visual acuity were determined, and a complete ophthalmological checkup including slit-lamp examination and funduscopy was performed. ATA and AQD measurements were performed only in the patient's right eye with each of the three devices under analysis.

The Anterion SS-OCT (version 1.2) makes B-scans of the eye using a 1,300-nm light source, with axial and lateral resolutions of less than 10 and 30 µm, respectively, a lateral scan angle of up to 16.5 mm wide, and a scan depth range of 14 ± 0.5 mm. The Visante TD-OCT (version 3.0.1.8) provides cross-sectional images using low-coherence interferometry with a wavelength of 1,310 nm. The axial and lateral resolutions are 18 and 60 µm, respectively, and measurements are up to 16 mm wide and 6 mm deep. The Pentacam HR (version 1.22r05) is based on the Scheimpflug principle and uses a rotating camera (1.45 megapixels) with a 475-nm monochromatic slit of light to illuminate the anterior segment. It captures 100 images in 2 seconds to calculate a three-dimensional model.

All measurements were obtained at Oftalvist (Spain). For each patient, the same skilled operator took all measurements during the same session. The order in which the three devices were used to record ATA distance and AQD readings was random. Calibration of the instruments was done prior to each measurement session following the manufacturer's recommendations. ATA distance was measured manually using the three devices and AQD was measured manually using the Visante TD-OCT and automatically with the SS-OCT and Pentacam. The operator was unaware of the objective of the study (masked to the identities and examination results) and the procedure followed was the same for the three devices. Manual values were analyzed from all patients per each device individually. For analysis purposes, ATA distance along the horizontal meridian and AQD were measured following previous studies.10–12 Moreover, ATA distance along the vertical meridian was also measured in 30 of the eyes included in the study. Figure A (available in the online version of this article) illustrates an example of ATA distance and AQD readings recorded with the Anterion SS-OCT (top), Visante TD-OCT (middle), and Pentacam (bottom). All parameters were registered and included in a database for their later analysis.

Angle-to-angle and aqueous depth distances at the horizontal meridian measured with the Anterion SS-OCT (Heidelberg Engineering GmbH) (top), Visante TD-OCT (Carl Zeiss Meditec AG) (middle), and Pentacam HR Scheimpflug camera (Oculus Optikgeräte GmbH) (bottom).

Figure A.

Angle-to-angle and aqueous depth distances at the horizontal meridian measured with the Anterion SS-OCT (Heidelberg Engineering GmbH) (top), Visante TD-OCT (Carl Zeiss Meditec AG) (middle), and Pentacam HR Scheimpflug camera (Oculus Optikgeräte GmbH) (bottom).

The statistical analysis was performed using the SPSS software (version 22.0, IBM Corporation). All results are given in the form of mean value ± standard deviation (SD). Potential statistically significant differences across the three devices were explored with the non-parametric Friedman test according to the sample distribution. The Tukey procedure was used as a post hoc test to compare different data groups when the Friedman test revealed significant differences between measurements. This method makes it possible to obtain the significance level for paired differences between the individual conditions. A P value of less than .05 was considered to be statistically significant. Agreement between devices was evaluated following the method suggested by Bland and Altman.13,14 The average and the difference between the measurements for all possible pairwise comparisons using the three devices were calculated. Different values were depicted on the plot: average difference, 95% CI of the average difference, and 95% limits of agreement (LoA, as mean difference ± 1.96 SD). The sample size for agreement studies was calculated following the indications provided by McAlinden et al.15 We considered the desired CI for the LoA in our study to be 0.10 mm. Based on this value and on the SD for the differences obtained in a first subset of 25 eyes, the sample size required for the agreement was at least 54 eyes.

Results

A total of 60 eyes from 60 patients (36 women, 24 men) were included in the study. The patients' mean age was 62.15 ± 17.06 years (range: 22 to 86 years). No complications occurred during the measurement process with any of the three instruments evaluated. Mean spherical equivalent was −1.76 ± 5.51 D (range: +5.51 to −22.50 D). Table 1 shows mean values, ranges, and the 95% CI for the horizontal ATA distance obtained with the three devices (Visante TD-OCT, Anterion SSOCT, and Pentacam HR) and the vertical ATA distance yielded by the two OCT platforms. AQD values are also shown as measured with those three devices.

ATA Distance and AQD Measurements for the Different Devices

Table 1:

ATA Distance and AQD Measurements for the Different Devices

The Friedman test revealed statistical differences when the ATA distance values were compared across the three devices (P < .001). The post hoc analysis with the Tukey test revealed statistically significant differences between the Visante TD-OCT and the Pentacam HR and between the Anterion SS-OCT and the Pentacam HR (P < .001). However, no statistically significant differences were found between the Visante TD-OCT and the Anterion SS-OCT (P = 1.00). The Pentacam HR produced smaller values (approximately 0.9 mm difference; Table 2) than the other two devices. The analysis for vertical ATA distance values revealed that there were no statistically significant differences between the Anterion SS-OCT and the Visante TD-OCT (P = .983). As far as the horizontal versus vertical ATA distance comparison is concerned, for the two OCT platforms there were statistically significant differences between the two parameters. More specifically, larger values along the vertical meridian were obtained (approximately 0.6 mm; Table 2). As for AQD, we also found statistically significant differences across the three devices (P < .001). More specifically, the post-hoc analysis showed differences between all pair-wise comparisons: Visante TD-OCT versus Anterion SS-OCT (P = .004), Visante TD-OCT versus Pentacam HR (P < .001), and Anterion SS-OCT versus Pentacam HR (P < .001).

Agreement of ATA Distance and AQD Measurements Between the Three Devices

Table 2:

Agreement of ATA Distance and AQD Measurements Between the Three Devices

Figure B (available in the online version of this article) shows the Bland-Altman plots (mean difference vs average) for all pair-wise comparison of ATA distance values yielded by the devices: Visante TDOCT versus Anterion SS-OCT for both horizontal- and vertical-meridian measurements, Visante TD-OCT versus Pentacam HR for the horizontal meridian, and Anterion SS-OCT versus Pentacam HR for the horizontal meridian. Similarly, Figure C (available in the online version of this article) shows the Bland-Altman plots (mean difference vs average) for all pair-wise comparison of AQD values yielded by the devices. Table 2 shows the detailed values for mean difference ± SD, 95% CI, and 95% LoA computed for all comparisons. The lowest mean differences in ATA distance were found between the Visante TD-OCT versus Anterion SS-OCT (0.0068 and −0.0415 mm, for horizontal and vertical meridians, respectively) and the highest between the Pentacam HR and the two OCT devices (approximately 0.9 mm). The widest LoA ranges were those that compared an OCT with the Pentacam HR (Figure B). Regarding AQD, the mean differences were similar for the Visante TD-OCT versus Anterion SSOCT, and the Anterion SS-OCT versus Pentacam HR comparisons (approximately 0.02 mm), and it was larger for the Visante TD-OCT versus Pentacam HR (approximately 0.05 mm) comparison. The LoA ranges followed the same trend, being larger for Visante TDOCT versus Pentacam HR (Figure 3).

Bland-Altman plots obtained showing the mean difference versus average for the comparison between the different devices measuring horizontal and vertical angle-to-angle distance. Mean (continuous line), lower and upper limits of agreement (±1.96 standard deviation, standard deviation, peripheral dotted lines), and lower and upper confidence intervals (95%) are depicted. The Anterion SS-OCT is manufactured by Heidelberg Engineering GmbH, the Visante TD-OCT is manufactured by Carl Zeiss Meditec AG, and the Pentacam HR Scheimpflug camera is manufactured by Oculus Optikgeräte GmbH.

Figure B.

Bland-Altman plots obtained showing the mean difference versus average for the comparison between the different devices measuring horizontal and vertical angle-to-angle distance. Mean (continuous line), lower and upper limits of agreement (±1.96 standard deviation, standard deviation, peripheral dotted lines), and lower and upper confidence intervals (95%) are depicted. The Anterion SS-OCT is manufactured by Heidelberg Engineering GmbH, the Visante TD-OCT is manufactured by Carl Zeiss Meditec AG, and the Pentacam HR Scheimpflug camera is manufactured by Oculus Optikgeräte GmbH.

Bland-Altman plots obtained showing the mean difference versus average for the comparison between the different devices measuring aqueous depth distance. Mean (continuous line), lower and upper limits of agreement (±1.96 standard deviation, standard deviation, peripheral dotted lines), and lower and upper confidence intervals (95%) are depicted. The Anterion SS-OCT is manufactured by Heidelberg Engineering GmbH, the Visante TD-OCT is manufactured by Carl Zeiss Meditec AG, and the Pentacam HR Scheimpflug camera is manufactured by Oculus Optikgeräte GmbH.

Figure C.

Bland-Altman plots obtained showing the mean difference versus average for the comparison between the different devices measuring aqueous depth distance. Mean (continuous line), lower and upper limits of agreement (±1.96 standard deviation, standard deviation, peripheral dotted lines), and lower and upper confidence intervals (95%) are depicted. The Anterion SS-OCT is manufactured by Heidelberg Engineering GmbH, the Visante TD-OCT is manufactured by Carl Zeiss Meditec AG, and the Pentacam HR Scheimpflug camera is manufactured by Oculus Optikgeräte GmbH.

Discussion

The main purpose of this study was to find out how interchangeable these three different devices are when it comes to measuring ATA distance. Our results revealed that the Pentacam HR produces significantly shorter ATA distance values (approximately 0.9 mm) than the two OCT devices, meaning that these devices cannot be used interchangeably for ATA distance measurements. This should be kept in mind when using these devices to calculate phakic IOL size, which usually varies in 0.50-mm steps. Pair-wise comparison analysis revealed that both OCT devices produced similar values; thus, they can be used interchangeably for ATA distance measurements along both the horizontal and vertical meridians. Note for example the small LoA found between both OCT devices shown in Figure B and Table 2. In contrast, the comparison of both OCT devices with the Pentacam HR showed wide ranges of LoA, being in some cases larger than 1.5 mm. In relation to the measurements at different meridians, our results showed that the vertical meridian was larger than the horizontal meridian (approximately 0.6 mm), showing that the anterior segment is vertically oval. These results agree with those reached in previous studies measuring the difference between horizontal and vertical ATA distance with TD-OCT16 and ultrasound biomicroscopy (UBM).17,18 Baikoff et al16 reported a mean difference of 0.30 mm in a sample of 36 eyes, and Oh et al17 and Petermeier et al18 found a mean difference of 0.45 mm using a 35-MHz UBM for a sample of 28 eyes and 0.22 mm using a 50-MHz UBM in a sample of 50 pseudophakic eyes, respectively.

This is the first study that compares these three devices for ATA distance measurements. In fact, there are few studies that evaluated the agreement of other devices to measure it. Piñero et al19,20 determined the interchangeability of the Artemis 2 (ArcScan, Inc) UBM and the Visante TD-OCT in 20 eyes (20 patients). ATA distance measurements obtained with both devices were well correlated with no statistically significant differences between them (P = .69). Mean values were 12.23 ± 0.59 and 12.14 ± 0.52 mm with the Artemis 2 and the Visante TD-OCT, respectively (LoA was 0.80). They concluded that both devices can be used interchangeably, although there was a slight tendency toward larger ATA distance values with the UBM device.

Domínguez-Vicent et al21 assessed the agreement between the Cirrus HD-OCT 5000 (Carl Zeiss Meditec) and the Sirius Scheimpflug camera (Costruzione Strumenti Oftalmici) in a sample comprising 80 healthy eyes (80 patients). They found that the Sirius measured significantly larger ATA distances (0.27 mm) than the Cirrus HD-OCT. The reported LoA ranged from −0.42 to 0.96 mm, which is similar to the values found by us for the Visante TD-OCT versus Pentacam HR (from 0.13 to 1.6 mm) and for the Anterion SS-OCT versus Pentacam HR (from 0.21 to 1.58 mm) comparisons. Thus, they concluded that the Cirrus HD-OCT and Sirius Scheimpflug camera cannot be used interchangeably to measure ATA distances for anterior chamber lens size calculation.

Domínguez-Vicent and Brautaset22 evaluated the same instruments in a sample of 60 eyes (60 patients) as a function of the patients' refractive error and reported similar values: the Cirrus gave on average between 0.4 and 0.6 mm larger ATA distances than the Sirius (Cirrus with a maximum 1.4 mm shorter and 0.6 mm larger ATA distance than Sirius). In a sample of 20 eyes (10 patients), Xu et al23 showed a low agreement between the Casia2 SS-OCT (Tomey Corporation) and the spectral-domain OCT Spectralis (Heidelberg Engineering GmbH) devices (mean difference of −0.20 mm, 95% CI from −0.02 to −0.41 mm and LoA from −0.53 to −0.13 mm). Mean values were 11.69 ± 0.21 and 11.88 ± 0.15 mm for Casia2 and Spectralis, respectively. The authors speculated that the low agreement was due to the variability in the scan location. The difference in the wavelengths of the Spectralis (880 nm) and the Casia2 (1,310 nm) also may contribute to the greater span of LoA found in their study.

Chansangpetch et al24 studied the agreement of the Casia2 and Visante TD-OCT in 53 eyes from 41 patients. They analyzed the images with customized automatic software to identify the temporal and nasal scleral spurs. They found a moderate agreement for anterior chamber width (scleral spur-to-scleral spur distance), showing in their Bland-Altman plots a minimal mean difference between both devices (Casia2: 11.68 ± 0.388 mm and Visante TD-OCT: 11.754 ± 0.432 mm). The mean difference was −0.067 mm (95% CI from −0.136 to 0.03 and LoA from −0.573 to 0.440), and thus the authors concluded that there was evidence of a proportional and constant bias and did not recommend that the measurement values be used interchangeably across the devices. These authors discussed in detail the possible sources of discrepancies (ie, technology, axis for centering the scan, accommodation induced by internal fixation, and the software algorithm). This should be kept in mind when comparing with the outcomes we have found in our study because the distances and methodology are different.

Zhang et al25 recently analyzed the agreement of the Visante TD-OCT with the Casia SS-1000 (Tomey Corporation) in 97 eyes of 49 myopic patients before Implantable Collamer Lens (STAAR Surgical) implantation. They concluded that both devices are interchangeable for ATA distance measurements, showing a mean difference of −0.008 mm with LoA from −0.250 to 0.232 mm.

Our results, comparing the Visante TD-OCT and the Anterion SS-OCT, showed slightly better outcomes for the mean differences and for the 95% CI and LoA ranges (see Table 2 for detailed values). It seems that when comparing two OCT platforms, the agreement is better than that resulting from comparing one of the OCT platforms with other technologies, such as Scheimpflug photography. Saito et al26 compared the ATA distances measured with the Casia2, the Pentacam HR, and the Scheimpflug TMS-5 (Tomey) devices in 26 eyes (26 healthy patients). ATA distance was determined automatically by the Casia2 and manually by the other two devices. The ATA distance in the Casia2 group (11.72 ± 0.32 mm) was significantly larger than that obtained in the Pentacam group (11.32 ± 0.45 mm, P = .016) or in the TMS-5 group (11.16 ± 0.40 mm, P < .001). In contrast, no significant differences were reported between the Scheimpflug devices (P = .420). They concluded that these three devices cannot be used interchangeably for ATA distance determination; more specifically, they reported that ATA distance values yielded by the SS-OCT Casia2 was 0.40 and 0.56 mm larger than those given by the Pentacam and the TMS-5, respectively. These findings are in good agreement with our results, although in our study the differences were even higher (approximately 0.9 mm).

As for AQD, we found statistically significant differences between devices. Bearing in mind the reported mean differences and LoAs, we consider that only the two OCT devices can be used interchangeably, but not the Pentacam HR. However, it is mandatory that a clinical criterion be identified to judge whether the differences reported among these three devices can be considered non-relevant for the three instruments to be used interchangeably. For example, Pentacam HR gave AQD readings up to 0.17 mm above or 0.07 mm below that given by the Visante TD-OCT. The range of LoA was 0.19 and 0.24 mm when the Pentacam HR was compared with the Visante TD-OCT and the Anterion SS-OCT, respectively. This range was narrower (0.13 mm) between the two OCT devices (Table 2).

In relation to the AQD analysis, we want to point out that there are a few studies showing the agreement between devices that are based on different optical technologies (eg, TD-OCT, SS-OCT, Scheimpflug, partial coherence interferometry, or low coherence reflectometry). In the following discussion, we have selected only those comparative studies that included—but were not limited to—at least two of the technologies used in our research. Note also that some of them analyzed the ACD, which considers values from the corneal epithelium up to the crystalline lens. Notwithstanding, we report mean differences between devices and not mean values.

Doors et al27 compared the Visante TD-OCT and Pentacam devices in 66 healthy eyes (33 patients) and 42 eyes after iris-fixated phakic IOL implantation (22 patients), indicating that both devices should not be used interchangeably for ACD measurement in either healthy patients or after phakic IOL implantation (mean difference of 0.07 and 0.10 mm, and LoA from 0.15 to −0.01 and 0.25 to −0.06 mm, respectively). Fu et al28 evaluated 50 eyes (50 patients), concluding that the agreement between both instruments was not sufficient (Pentacam's ACD value was 0.8 mm lower than the Visante TD-OCT device). Dinc et al29 found in 80 eyes (40 patients) that the Visante TD-OCT and Pentacam ACD measurements were comparable (95% LoA: −0.019 to 0.056 mm). Yazici et al30 also analyzed the same devices in 100 healthy eyes (50 patients) and reported similar differences (mean: −0.04 mm, P = .703, and LoA: 0.20 to −0.27 mm). For a small sample of 27 eyes (27 patients), O'Donnell et al31 reported that the Pentacam may give ACD values up to 0.11 mm above or 0.17 mm below the reading obtained with the Visante TD-OCT. Wang et al32 evaluated 71 eyes (71 patients) and also reported significant differences with a mean value of −0.04 mm (P < .01) and LoA from −0.14 to 0.06 mm, but concluded that both devices can be used interchangeably in most clinical situations. In contrast, Shajari et al33 evaluated 40 eyes (40 patients) and found no significant differences (mean difference of 0.1 mm, P = .20). Wan et al34 compared both devices in 82 eyes (82 patients) implanted with a posterior chamber phakic IOL and showed a mean difference of 0.25 mm with LoA from 0.13 to 0.28 mm (small values for Pentacam). Our results revealed significant differences between the Visante TD-OCT and the Pentacam HR, with a mean difference of 0.05 mm and LoA ranging from −0.07 to 0.17 mm. Hence, as suggested by other authors, these two devices should not be considered to be equivalent from a clinical point of view.

In addition to these studies, the Pentacam was also compared with the Casia SS-1000 SS-OCT in several studies, which reached the same conclusions.35,36 Szalai et al35 analyzed 57 eyes of 57 healthy patients and 84 eyes of 56 patients with keratoconus, showing statistically significant differences between devices in both groups: mean differences being 0.13 and 0.21 mm, and LoA ranging from −0.31 to 0.57 mm and from −0.09 to 0.50 mm, respectively (P < .0001). Nakakura et al36 also analyzed 42 eyes (42 patients) with those same devices, concluding that they were not interchangeable for both automatically and manually calculated ACD: mean difference of 0.10 and 0.12 mm, and LoA from −0.04 to 0.24 and from −0.02 to 0.27 mm, respectively.

A few studies that have compared two SS-OCT models also concluded that they were not interchangeable. For example, Aptel et al37 reported data on 101 eyes (101 healthy patients) whose ACD was measured with two OCT devices, the Visante TD-OCT and the Casia SS-1000. They found a significant bias, with the Casia SS-1000 producing consistently higher values. Nowinska et al38 compared both devices in 50 eyes (50 healthy patients) and 96 eyes (54 patients with corneal dystrophies) and also found statistically significant differences between both devices (P < .01, mean differences being 0.07 and 0.06 mm, respectively). Angmo et al39 analyzed 72 eyes (36 patients) with primary angle closure disease and, despite their finding a good correlation between devices, the LoA was wide (from −0.20 to 0.20 mm). Zhang et al25 compared both devices, concluding that they are interchangeable for ACD measurement and reporting a mean difference of −0.006 mm with LoA from −0.135 to 0.121 mm. In a sample of 53 eyes (51 patients), Chansangpetch et al24 analyzed the agreement between the Visante TDOCT and the Casia2. They showed a mean difference of 0.018 mm with LoA ranging from 0.057 to −0.093 mm (Casia2 values being higher than Visante TD-OCT values) in agreement with previous studies found in the literature.37–39

It is plausible that the inter-device differences found in our study and those reported by other authors may stem from the different optical technologies or methodologies used. Resolution and variability in the number of scans, light reflected on the iris, and the manual versus the automatic detection of the structure to be measured all may play a significant role that would contribute to the reported discrepancies for some of the comparisons. Also, because ACD varies with accommodation, it should be carefully controlled. For example, it is interesting to adjust the focus of the fixation target with the patients' refraction, maintaining fixation at a fixed target during the measurement. Pentacam and Anterion SS-OCT AQD readings are automatically calculated by the device, whereas the value has to be measured manually with the Visante TD-OCT.

However, finding differences between devices does not necessarily mean that they have a clinical significance in daily practice in situations such as predicting an optimal phakic IOL size, calculating IOL power based on new generation formulas, or the anterior segment assessment in patients with specific diseases (ie, glaucoma). In our opinion, this should be evaluated on an individual basis. For example, a 0.1-mm difference in ACD would lead to approximately 0.15 diopters (D) of refraction change for IOL power calculation.40 The width of our LoA was 0.13, 0.24, and 0.19 mm for the three comparisons. These values, in the worst-case scenario, would lead to a change in refraction of approximately 0.25 D, which is clinically acceptable. However, these ranges cannot be assumed to be negligible when considering for instance the safety distance in a patient to be implanted with a phakic IOL. Consequently, clinicians should always keep in mind not only the mean difference, but also the LoA between devices.

Our study has a few limitations. For example, the ATA distance measurement was done on the horizontal and vertical meridians and no other orientations have been evaluated. In addition to performing measurements along different orientations, future studies should include larger samples, a wider patient age and refraction ranges, and, if possible, more devices used in clinical practice to be compared.

Our study shows that there were statistically significant differences in ATA distance and AQD measurement among the three devices used. Specifically, Visante TD-OCT and Anterion SS-OCT are interchangeable for ATA distance measurement, but Pentacam HR is not with either of the two OCT devices. For AQD measurement, a clinical criterion should assess whether these three devices could be used interchangeably.

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ATA Distance and AQD Measurements for the Different Devices

ParameterVisante TD-OCTAnterion SS-OCTPentacam HRPa
ATA distance (mm)
  Horizontal
    Mean ± SD11.96 ± 0.4711.96 ± 0.4211.05 ± 0.44< .001b
    Range10.88 to 13.1010.97 to 12.7710.17 to 12.01
    95% CI11.84 to 12.0811.85 to 12.0610.94 to 11.16
  Vertical
    Mean ± SD12.61 ± 0.6512.65 ± 0.51.983
    Range11.13 to 13.7411.60 to 13.61
    95% CI12.36 to 12.8612.45 to 12.85
AQD (mm)
  Mean ± SD2.86 ± 0.482.83 ± 0.492.79 ± 0.50< .001b
  Range2.06 to 4.292.00 to 4.261.97 to 4.26
  95% CI2.73 to 2.982.71 to 2.962.66 to 2.92

Agreement of ATA Distance and AQD Measurements Between the Three Devices

ParameterMean ± SD Difference95% CI95% LoA
ATA distance (mm)
  Visante TD-OCT vs Anterion SS-OCT (horizontal)0.0068 ± 0.1817−0.0396 to 0.0532−0.3494 to 0.3629
  Visante TD-OCT vs Pentacam HR (horizontal)0.9105 ± 0.39580.8095 to 1.01150.1347 to 1.6862
  Anterion SS-OCT vs Pentacam HR (horizontal)0.9037 ± 0.34930.8146 to 0.99290.2191 to 1.5883
  Visante TD-OCT vs Anterion SS-OCT (vertical)−0.0415 ± 0.2858−0.1493 to 0.0663−0.6017 to 0.5186
AQD (mm)
  Visante TD-OCT vs Anterion SS-OCT0.0217 ± 0.03450.0129 to 0.0305−0.0459 to 0.0893
  Visante TD-OCT vs Pentacam HR0.0502 ± 0.06330.0340 to 0.0663−0.0739 to 0.1742
  Anterion SS-OCT vs Pentacam HR0.0263 ± 0.04860.0139 to 0.0387−0.0689 to 0.1215
Authors

From Oftalvist, Alicante, Spain (PT-R, MDR-C, MR-S, BG-T); and the Optics and Optometry & Vision Sciences Department, University of Valencia, Valencia, Spain (RM-M).

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

AUTHOR CONTRIBUTIONS

Study concept and design (PT-R, MDR-C, MR-S, BG-T, RM-M); data collection (PT-R, MDR-C, BG-T); analysis and interpretation of data (PT-R, MDR-C, MR-S, BG-T, RM-M); writing the manuscript (PT-R, RM-M); critical revision of the manuscript (PT-R, MDR-C, MR-S, BG-T, RM-M)

Corrspondence: Robert Montes-Micó, PhD, Optics and Optometry & Vision Sciences Department, University of Valencia, C/Dr Moliner 50, 46100 Valencia, Spain. Email: Robert.montes@uv.es

Received: May 26, 2020
Accepted: October 08, 2020

10.3928/1081597X-20201013-01

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