DOI: https://doi.org/10.21203/rs.3.rs-2049518/v1
This study aimed to assess the agreement between biometric parameters measured by a spectral-domain OCT optical biometer device (Optopol Revo NX) with a validated Swept-source biometer (IOLMaster 700) and a validated optical low coherence reflectometry (OLCR) biometer (Lenstar LS 900), in cataract surgery candidates.
In this prospective comparative study, 100 patients (100 eyes) who were eligible for cataract surgery were involved. Bland Altman analysis was used to assess agreement between devices for biometric parameters including axial length (AL), anterior chamber depth (ACD), lens thickness (LT), and central corneal thickness (CCT).
AL measurements were successful in 82 eyes (82.0%) with Revo NX, in 91 eyes (91.0%) with Lenstar LS 900, and in 97 eyes (97.0%) with IOL Master 700. When Revo NX was compared to IOLMaster 700 and Lenstar LS 900, the mean differences were as follows: -0.02 ± 0.0.02 and − 0.02 ± 0.03 for AL, 0.01 ± 0.03 and 0.10 ± 0.03 (p < 0.05) for ACD, -0.15 ± 0.03 (p < 0.05) and 0.001 ± 0.04 for LT, and − 2.29 ± 0.92 (p < 0.05) and 0.73 ± 1.43 for CCT. There was a good correlation between devices for AL, ACD, LT, and CCT (ICC > 0.75). Bland-Altman analysis showed a narrower 95% limit of agreement (-0.35 to 0.31) between Revo NX and IOL Master 700 in measuring AL.
Despite the higher measurement failure rate in eyes with cataract, the Revo NX showed very good agreement with the IOL Master 700 and Lenstar LS 900 optical biometers in measuring AL, ACD, LT, and CCT. However, ACD and LT measurements can not be considered interchangeable between these devices.
In an era of modern cataract surgery, accurate biometric measuremnets of the eye are instrumental for acucurate determination of intraocular lens (IOL) power and optimised refractive outcomes.1 Axial length (AL) and anterior chamber depth (ACD) can be measured with ultrasound, partial coherence interferometry (PCI), optical low-coherence reflectometry (OLCR), and recently optical coherence tomography (OCT) devices.2
Since the introduction of the IOL Master (Carl Zeiss Meditec AG, Germany) in 1999, optical biometry has for a long period of time been a gold standard in ocular biometry measurements.3 IOL Master 700 was the first swept-source OCT (SS-OCT)-based biometry device, which acquired OCT images across the entire length of the eye.4 Although the IOLMaster 700 provides excellent anterior segment OCT images, it cannot offer high-quality scans of the retina and optic nerve, simultaneously.
Lenstar LS 900 (HAAG-STREIT AG, Switzerland) works based on OLCR technology. It combines optical biometry with automated keratometry.5 The agreement, validity, and interchangeability of IOL master 700 and Lenstar LS 900 have been reported in previous studies.4,6−8
The recently introduced Revo NX device (OPTOPOL Technology Sp, Poland) is a combination of anterior and posterior segment spectral-domain OCT (SD-OCT) with optical biometry.5 The Revo NX is the first Anterior/Posterior OCT system that enables simultaneous measurement of AL, ACD, lens thickness (LT), and central corneal thickness (CCT).9 The biometric measurement provided by the previous version (software version 8.0.3) of Revo NX biometer were found not to be in agreement with Lenstar LS 900.5 After improving its calibration by the manufacturer, the upgraded version (9.5.0) claims to be able to compete with other devices, and a recent study, comparing the upgraded version of Revo NX optical biometer with the two other validated optical biometers (e.g. IOL Master 700 and Lenstar LS 900) found a good agreement between devices in healthy individuals.3 This study sought to assess the acquisition success rate and agreement of biometry measurements obtained by REVO NX biometer (software version 9.7.0) with IOL Master 700 and Lenstar LS 900 in cataract surgery candidates.
This prospective study was performed on patients presenting for cataract surgery between November 2019 and September 2020 at Noorafarin eye Clinic (Mashhad, Iran). The study was approved by the Ethics Committee of Mashhad University of Medical Science (Ethical code: IR.MUMS.fm.REC.1396.793(. Cataract types and grading were recorded according to Lens Opacities Classification III scoring system (LOCS III). 10 Patients were invited to participate in the study after an explanation of the study and its purpose. All participants gave informed consent to participate in research and the research followed the tenets of the Declaration of Helsinki. For all patients a full medical and ocular history was taken. All patients underwent a full anterior and posterior segment slit-lamp examination as well as macula and optic disc OCT scans.
One hundred patients with cataract over the age of 50 were included. Eyes were excluded if ocular co-morbidities were expected to alter biometry measurements. Eyes with the following pathologies were excluded: pterygium, corneal transplantation, corneal dystrophy, keratoconus and corneal scarring. Patients were also excluded if they were unable to fixate on the fixation target.
All biometry examinations were performed in a random order, by one experienced operator between 4–8 PM. During the procedure, patients were asked to steadily fixate to the fixation light and blink to provide a continuous tear layer. All exams were repeated three times and the results were averaged. Focused and high-quality images were included and the results were averaged for the statistical analysis. AL, ACD, LT, and CCT parameters were extracted for the agreement analysis.
The Revo NX SD-OCT device has an axial resolution of 5 mm, a transverse resolution of 12 mm, and a scanning depth of 2.4 mm. It can produce 110,000 scans per second. The optical biometry program within the device measures the AL, ACD, LT, and CCT. It performs 10 B-scans for each measurement to calculate a precise mean value.9
Lenstar LS-900 OLCR biometer uses a superluminescent diode with 820 nm wavelength to measure the AL, LT, CCT, and ACD, and also provides KR values and pupil size.11 IOL Master 700 measures AL, and ACD along with CCT and LT using an adjustable 1050 nm laser infrared light and multi-point keratometer, acquiring over 2000 scans per second.9
Statistical analysis was performed using SPSS 23 software (SPSS Institute, Inc., Chicago, IL, USA), and MedCalc software (Version 20; MedCalc Inc., Ostend, Belgium). Kolmogorov-Smirnov test was used to assess the parametric distribution of data. Repeated measures analysis of variance (ANOVA) and Bonferroni posttest were used to assess the difference between devices. The measured data of each device were plotted by Bland - Altman diagram to investigate the qualitative distribution and compare the compatibility or dispersion of data provided by Revo NX compared to IOL Master 700 and Lenstar LS 900. The mean ± 1.96 standard deviation (SD) of the difference between the two measurement techniques, defined the 95% limits of agreement. The mountain plots were used to show the measurement differences between devices. Depending on the numerical value of SD, the agreement range was much narrower or wider. The interclass correlation coefficient (ICC) was defined as the ratio of the variance between subjects to the sum of the pooled intra- and inter-participant variance. ICC more than 0.9 is defined as a high agreement, between 0.7–0.9 considered a good agreement, and an ICC less than 0.7 considered a poor agreement between measurement techniques.12 A P-value less than 0.05 was considered statistically significant.
Based on the previous studies4, the sample size calculation performed to detect a mean difference of 0.01 mm of axial length with a standard deviation of 0.02 mm, with a power of 80% and significance level of 0.05 using the Bland-Altman method, revealed a minimum sample size of 83 is needed for each group within a paired analysis.
One hundred patients (100 eyes) including 55 women (55.0%) and 45 men (45.0%) with a mean age of 61.85 ± 7.90 years (range 50–82 years) were included. AL was successfully measured in 82% of the patients using Revo NX biometer, 91.0% of patients using Lenstar LS 900, and 97.0% of all patients using IOL Master 700. Table 1 shows baseline characteristics of ocular biometric parameters measured using the three devices. The mean of LT and ACD were significantly different between the three devices (p < 001 and p = 0.005 respectively). Table 2 shows paired difference and agreement between parameters measured with the three devices. Bonferroni test showed a significant difference between IOL Master and Revo NX in LT measurement (p < 0.05). Also, ACD measured using Revo NX was significantly higher than Lenstar (p = 0.007).
| AL (mm) | LT (mm) | ACD (mm) | CCT (µm) | |||||
|---|---|---|---|---|---|---|---|---|
| Mean ± SD | Range | Mean ± SD | Range | Mean ± SD | Range | Mean ± SD | Range | |
| Revo NX | 23.46 ± 0.18 | 21.21–32.67 | 4.15 ± 0.04 | 3.34–5.15 | 3.25 ± 0.05 | 2.15–4.78 | 520.02 ± 3.37 | 438–595 |
| Lenstar LS 900 | 23.48 ± 0.18 | 21.27–32.50 | 4.15 ± 0.05 | 3.27–5.27 | 3.15 ± 0.05 | 2.04–4.76 | 519.29 ± .3.37 | 438–601 |
| IOL Master 700 | 23.48 ± 0.17 | 21.22–32.48 | 4.30 ± 0.04 | 3.29–5.40 | 3.24 ± 0.05 | 1.89–4.68 | 522.31 ± 3.32 | 441–603 |
| p-value* | 0.625 | < 0.001 | 0.005 | 0.06 | ||||
| *Repeated measures ANOVA | ||||||||
| Paired difference* with Revo NX | Agreement with Revo NX | |||||
|---|---|---|---|---|---|---|
| Lenstar LS 900 | IOL Master 700 | Lenstar LS 900 | IOL Master 700 | |||
| Mean ± SD | Mean ± SD | 95%LOA | ICC | 95%LOA | ICC | |
| AL (mm) | -0.02 ± 0.03 | -0.02 ± 0.0.02 | -0.46 to 0.43 | 0.989 | -0.35 to 0.31 | 0.994 |
| LT (mm) | 0.001 ± 0.04 | -0.15 ± 0.03** | -0.55 to 0.53 | 0.750 | -0.69 to 0.39 | 0.770 |
| ACD (mm) | 0.10 ± 0.03** | 0.01 ± 0.03 | -0.59 to 0.62 | 0.810 | -0.47 to 0.67 | 0.80 |
| CCT (µm) | 0.73 ± 1.43 | -2.29 ± 0.92** | -26.20 to 27.70 | 0.910 | -19.70 to 15.10 | 0.960 |
| *Bonferroni multiple comparisons; **p-value < 0.05 | ||||||
All parameters measured with Revo NX biometer were in high agreement with Lenstar and IOL Master (Table 2). A high degree of agreement was found between Revo NX and the other 2 biometers in AL and CCT measurements (ICC > 0.90). This agreement was lower but good for LT and ACD measurements (ICC: 0.75–0.81).
The agreement of parameters between Optopol OCT, Lenstar, and IOL Master were assessed and represented using the Bland-Altman method (Fig. 1). Also, mountain plots showed high agreement between Revo NX and the two other devices for the measured biometric parameters (Fig. 2).
In this study, the biometric parameters measured by Revo NX biometer, Lenstar LS 900, and IOL Master 700, were compared in candidates presenting for cataract surgery. A good to a high agreement was found between devices, especially in the measurement of AL and CCT. The agreement of the IOL Master 700 and Lenstar LS 900 devices has also been previously investigated, and a high agreement between devices and no clinically relevant differences were found. 7,8
In the present study, the failure rate of IOL Master 700, Lenstar LS 900, and Revo NX OCT in measuring AL was 3%, 9%, and 18%, respectively. This is in keeping with previous studies showing that SS-OCT-based biometers, demonstrate greater penetration of the cataractous lens.13 Sikorski et al. also reported a higher failure rate of the SD-OCT Revo NX in measuring AL compared to the SS-OCT IOL Master 700 and proposed this to be due to the difference in OCT technology used by the Revo NX. 12
In the present study, AL measurements obtained by IOL Master 700 were marginally higher than the other devices, but the differences were not clinically and statistically significant. This is similar to the results reported by Kanclerz et al., comparing the same devices in healthy eyes.3 The authors found a high level of agreement (r value > 0.95) between Revo NX and IOL Master 700, and Lenstar LS 900 when measuring AL. Mean difference between − 0.001mm and 0.01 mm for AL measurement has been reported between Revo NX and IOL master 700. 3,12 In our study, the mean paired difference between AL measured by Revo NX and IOL Master 700 was − 0.02 mm. Moreover, mean difference of -0.02 mm was also found between Revo NX and lenstar LS 900 which is similar to the results of the study by Kanclerz at al,3,5 who found a mean difference of -0.002 to 0.11 mm when measuring AL in healthy eyes using Revo NX and Lenstar LS 900. Previous investigators have proposed a difference of 0.1 mm to be acceptable between AL measurements (almost equivalent to an error of about 0.27 D in intraocular lens power).14
In terms of CCT, a mean difference between Revo NX and IOL Master 700 of -2.29 µm (p < 0.05) was found. This is similar to previous studies reporting a mean difference between the two devices of -0.80 to -4.40 µm.3,12 The mean difference between Revo NX and Lenstar LS 900 was 0.73 µm which is consistent with other studies reporting a mean difference of between − 0.83 and 3.80 µm. 3,5 Although, differences in CCT measurements between these devices are not clinically significant, more difference in the measured CCT using Revo NX and IOL Master 700 has been justified with the several-fold smaller pixel size in Revo NX.12 The Optopol OCT Revo NX offers a resolution of 5 micrometers, which is more than four times better than the IOL Master 700 and enables it to define the boundaries of the layers of eye tissue more accurately. 12 Due to these capabilities, more accurate measurements can be made in the eyes with structural abnormalities or pathology. In this respect, the Revo NX surpasses the IOL Master 700 in measuring AL in irregularly structured eyes.12 More studies on the limitations and benefits of this device in comparison to other biometry systems are needed in patients with different cataract types and severities.
With respect to ACD, the mean difference of ACD measured with Revo NX and IOL Master 700 was 0.01 mm, and 0.10 mm as measured by the Revo NX and Lenstar LS 900. Other studies have reported a mean difference between 0.003 and 0.005 mm between Revo NX and IOL Master 700, and 0.01 to 0.05 mm between Revo NX and Lenstar LS 900.3,5,12 Depending on AL of the eye, a 0.25 mm error in ACD measurement results in a difference in IOL power between 0.50 to 1.0 D.15 Based on these findings, the differences in CCT measurements between the above platfroms are likely clinically insignificant.
Mean difference of LT between Revo NX and IOL Master 700 was − 0.15mm (p < 0.05), which is significantly more that previously reported (0.001–0.002 mm).3,5,12 The mean difference of LT measured with Revo NX and Lenstar LS 900 was 0.001 mm, and significanly less than similar studies which report a mean difference of between 0.008 and 0.03.3,5,12 The differences between our results and previous studies is likely related ot the fact that our study was performed on a cataractous group of patients. Dense lens and poor fixation may contribute to the ACD and LT measurment differences found in this study compared to previous studies. However, in the clinical practice, in IOL calculation formula which use LT parameter, a difference of 0.20 mm may change the IOL power by 0.20 dioper. 15 Based on these findings, statistically significant differences between Revo NX and IOL Master 700 may not considered clinically significant.
Previous studies show that Revo NX SD-OCT offers high repeatability and reproducibility in measuring ACDand LT in healthy eyes.5 It has been also reported to have a very strong correlation with the Lenstar LS 900 biometric measurements. However, AL and ACD measured with these devices were not considered interchangeable. 5 Similarly, we found a statistically and clinically significant difference between ACD measured with Revo NX and Lenstar LS 900 (0.10mm), but the AL measurement was in very good agreement. A newer version of Revo NX OCT was used in this study and there was a very good correlation between this device and IOL Master 700 in all measured biometric parameters (according to ICC). Also, narrower LoA was found between parameters measured using Revo NX and IOL Master 700 compared to the Revo NX and Lenstar LS 900. Strengths of the study include its prospective nature, the large number of eyes included and the inclusion of only eye per patient. However our study had a number of limitations including a lack of a healthy control group.
In conclusion, in eyes with cataract, despite the higher measurement failure rate, the Revo NX biometer showed very good agreement with the IOL Master 700 and Lenstar LS 900 validated optical biometers in measuring AL, ACD, LT, and CCT. However, ACD and LT measurements can not be considered interchangeable between these devices.
Acknowledgments
This study was supported by the research deputy of Mashhad University of Medical Sciences, Mashhad, Iran (grant number: 960395).
Conflict of interest
The authors declare that they have no conflict of interest.
Funding
The authors did not receive any financial support from any public or private sources.
The authors have no financial or proprietary interest in a product, method, or material described herein.