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Evaluation of the Agreement of Advanced Corneal Explorer with Pentacam and Orbscan in Myopic Individuals with Healthy Corneas
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Mohammad-Hosein Validad1    , Hava Shafiee2 , Monireh Mahjoob3 , Tahereh Rakhshandadi3 , Hadi Ostadimoghaddam *4 , Abbas-Ali Yekta5 , Javad Heravian Shandiz5 , Neda Nakhjavanpour2 , Sara Farsi2 |
1- Assistant Professor, Ophthalmologist, Department of Ophthalmology, Alzahra Eye Hospital, Zahedan University of Medical Sciences, Zahedan, Iran.
2- M.Sc in Optometry, Department of Optometry, School of Rehabilitation Sciences, Zahedan University of Medical Sciences, Zahedan, Iran.
3- Associate Professor, Ph.D in Optometry, Department of Optometry, School of Rehabilitation Sciences, Zahedan University of Medical Sciences, Zahedan, Iran.
4- Professor, Ph.D in Optometry, Refractive Error Research Center, Department of Optometry, School of Rehabilitation Sciences, Mashhad University of Medical Sciences, Mashhad, Iran. , ostadih@mums.ac.ir
5- Professor, Ph.D in Optometry, Refractive Error Research Center, Department of Optometry, School of Rehabilitation Sciences, Mashhad University of Medical Sciences, Mashhad, Iran. |
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Keywords: Cornea [MeSH], Corneal Topography [MeSH], Myopia [MeSH]
Article ID: Vol27-16 |
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Type of Study: Original Articles |
Subject:
Ophtalmology
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Abstract: (744 Views) |
Extended Abstract
Introduction
Today, measuring the topographic and tomographic parameters of the eye's anterior segment is crucial for diagnosing and managing corneal and ocular diseases, detecting and monitoring keratoconus, performing corneal transplants, fitting contact lenses, and implanting intraocular lenses. Additionally, accurate and reliable corneal thickness measurement is essential in corneal refractive surgery, especially for patients with high myopia. These applications underscore the significance of developing advanced topographic tools and methods for evaluating both the anterior and posterior corneal surfaces. Moreover, corneal imaging devices equipped with wavefront analysis can measure higher-order corneal aberrations. Corneal aberrations significantly impact visual quality and are known to increase considerably after refractive surgery. Various devices are currently employed to assess corneal parameters. The Advanced Corneal Explorer (ACE), a high-resolution swept-source optical coherence tomography (SS-OCT) device, has recently been introduced to the market. It offers high-quality assessment of the eye's anterior segment through multimodal imaging, utilizing an optimized platform to capture high-reolution images. Orbscan utilizes slit-scanning technology to sequentially capture 20 slit images of the cornea. These images are then employed by the device to reconstruct both the anterior and posterior corneal surfaces. Subsequently, corneal thickness is determined by subtracting the height of the anterior surface from the height of the posterior surface. Pentacam, utilizing a rotating Scheimpflug camera, provides quantitative data on both the anterior and posterior corneal surfaces. It is also capable of anterior chamber modeling and corneal biometry, the reliability of which in measuring central corneal thickness, anterior chamber depth, and anterior and posterior corneal curvature and power has been widely affirmed. Given the importance of accurate and reliable measurement of anterior segment parameters in the diagnosis and management of corneal diseases, this study was conducted to evaluate the agreement of ACE with Pentacam and Orbscan in myopic individuals with healthy corneas.
Methods
This descriptive-analytical study was conducted on 45 myopic individuals (25 females and 20 males) aged 20 to 40 years referring to Al-Zahra Ophthalmology Hospital in Zahedan, Iran, during 2023. The samples were selected using a convenience non-probability sampling method.
Initially, a comprehensive ocular examination, including slit-lamp biomicroscopy and fundoscopy, was performed by an ophthalmologist to assess overall ocular health. Subsequently, optometric examinations, including refractive error determination using an autorefractometer (Topcon KR-1), subjective refraction, recording of best corrected and uncorrected distance visual acuity in LogMAR, and all anterior segment imaging, were conducted by a skilled optometrist. Anterior segment imaging was performed using the ACE (ACE, Technolas Perfect Vision GmbH, München, Germany), a SS-OCT device with a high-wavelength light source (1300 nm), a Pentacam (Pentacam HR ,Oculus, Optikgeräte GmbH, Wetzlar, Germany), equipped with a 360-degree Scheimpflug camera mechanism, and an Orbscan II (Orbscan II, Bausch & Lomb, Orbtek Inc., Salt Lake City, United States), equipped with both Placido disc and scanning slit systems.
The corneal parameters investigated included corneal topography (mean power and maximum and minimum power of the anterior and posterior corneal surfaces), corneal tomography (central corneal thickness and thinnest corneal thickness), anterior corneal surface aberrations, total corneal aberrations, pupil diameter, and white-to-white distance.
To statistically assess the agreement of ACE data with two other devices, the intraclass correlation coefficient (ICC) and 95% limits of agreement (LoA) were employed. The ICC is a widely used reliability index in agreement analyses. An ICC of less than 0.75 is classified as poor agreement, an ICC between 0.75 and 0.90 as moderate agreement, and an ICC greater than 0.9 as good agreement. The 95% LoA were calculated as the mean difference ±1.96 time the standard deviation of the differences between the two measurement methods. According to previous studies, LoAs of ±0.5 dpt (range of 1 dpt) for corneal powers, ±10 µm (range of 20 µm) for corneal thickness, ±0.5 mm (range of 1 mm) for diameters, and ±0.1 µm (range of 0.2 µm) for aberrations were defined as clinically acceptable agreement between instruments. Further, Bland-Altman plots were utilized to illustrate the agreement of several key variables.
Results
The participants' mean spherical equivalent refractive error was −2.75 ± 1.45 dpt (range of −0.50 to −5.00 dpt), and the corrected distance visual acuity for all patients was 6.6.
The mean differences in corneal topography, tomography, and aberrations obtained by ACE were compared with Pentacam and Orbscan, including their ICCs and 95% LoA among participants.
Based on the ICC and 95% LoA, the ACE device demonstrated good statistical and clinical agreement with Pentacam for mean corneal anterior surface power (ICC = 0.97), maximum power (ICC = 0.98), and minimum power (ICC = 0.97). Similarly, it showed good agreement with Orbscan for mean corneal anterior surface power (ICC = 0.98), with 95% LoA (less than 1 dpt) (P < 0.001). However, ACE showed an intermediate ICC for maximum and minimum anterior corneal power (ICC = 0.76) and 95% LoA greater than 1 dpt difference with Orbscan. Clinically, the agreement between these two devices for maximum and minimum anterior corneal power was not acceptable.
The central corneal thickness and thinnest corneal thickness measurements obtained with ACE and Pentacam showed good statistical and clinical agreement, with ICCs of 0.99 and 0.95, respectively, and 95% LoA less than 20 microns. In contrast, the central corneal thickness and thinnest corneal thickness measurements obtained with ACE demonstrated good statistical agreement with Orbscan (ICCs of 0.95 and 0.97, respectively); however, 95% LoA of 51.58 and 37.9 microns obtained for the central corneal thickness and thinnest corneal thickness, respectively, indicated no significant clinical agreement between these devices.
The ICC values for white-to-white distance were found to be 0.81 for both the ACE and Pentacam devices and 0.58 for Anterion and Orbscan. Additionally, the 95% LoA between these devices were greater than 1 mm. The ICCs for pupil size between ACE and Pentacam were 0.14, and between ACE and Orbscan were 0.08, indicating very poor agreement.
Furthermore, anterior surface and total corneal aberrations exhibited poor agreement between ACE and Pentacam due to a low ICC (< 0.75) and a difference greater than 0.2 microns between the two devices for all aberrations.
Bland-Altman plots of corneal topography and tomography (the difference between the two values obtained for each individual versus the mean of the two values obtained for each individual) were generated between the ACE device and both Pentacam and Orbscan. The range between the upper and lower limits (95% LoA) for ACE with Pentacam was narrow for anterior and posterior corneal surface power, central corneal thickness, and thinnest corneal thickness, revealing good agreement between these two devices for these parameters. However, for other parameters, this range was wide, suggesting a lack of agreement between the devices.
Conclusion
Based on the results of the present study, ACE showed good clinical agreement with Pentacam for the mean power and the maximum and minimum anterior and posterior corneal power, and with Orbscan for the mean anterior corneal power. This was evidenced by high ICC values and 95% LoA less than 1 dpt. However, for other corneal topography parameters, ACE did not show good agreement with Orbscan in myopic individuals.
Our study's findings also revealed that ACE had good agreement with Pentacam for central corneal thickness and thinnest corneal thickness, due to good ICC values and a difference of less than 20 microns.
In our study, ACE exhibited no acceptable statistical and clinical agreement for white-to-white distance and pupil size with the Pentacam and Orbscan devices. A probable reason for the disagreement in pupil size measurements obtained by corneal imaging devices in this research and previous studies may be the lack of control over ambient lighting conditions during measurement. Although corneal imaging is generally performed in relative dim light conditions, placing a black cloth over the patient's head in a Pentacam device can culminate in greater pupil dilation due to increased darkness. This practice may lead to further pupillary dilation due to the increased darkness. Given that accurate pupil size measurement is particularly crucial for cataract surgeries, it is recommended that both the measurement device and the lighting conditions be recorded when this parameter is documented.
Corneal aberration measurements are crucial for assessing individuals' quality of vision, particularly after contact lens fitting and refractive surgery. Based on the results of this study, anterior and total corneal aberrations did not show good statistical and clinical agreement between the ACE and Pentacam devices, due to low ICC values and differences greater than 0.2 microns between the two devices.
Discrepancies between the studied devices may stem from differences in imaging technology, such as Scheimpflug technology in Pentacam, slit-scanning in Orbscan, and SS-OCT in ACE. Differences in data processing algorithms, sampling point density, and environmental factors may also influence the measurement results.
Ethical Statement
The study received approval from the Research Ethics Committee at Mashhad University of Medical Sciences (IR.MUMS.REC.1402.137). Patients were enrolled in the study after a comprehensive explanation of the study procedures and obtaining written informed consent.
Funding
This article has been extracted from the doctoral dissertation of Dr. Tahereh Rakhshandadi in Optometry at the School of Paramedical Sciences, Mashhad University of Medical Sciences. This study was funded by the Vice-Chancellor for Research and Technology, Mashhad University of Medical Sciences.
Authors' Contributions
Mohammad-Hosein Validad: Project administration and design.
Hava Shafiee: Drafting of the initial manuscript.
Monireh Mahjoob: Data analysis and interpretation of the results.
Tahereh Rakhshandadi: Project execution and data collection.
Hadi Ostadimoghaddam: Project administration and design and approval of the final manuscript.
Abbas-Ali Yekta: Project administration and design and approval of the final manuscript.
Javad Heravian Shandiz: Project administration and design and approval of the final manuscript.
Neda Nakhjavanpour: Interpretation of the results.
Sara Farsi: Interpretation of the results and approval of the final manuscript.
Conflicts of Interest
No conflicts of interest.
Acknowledgments
We would like to thank the Vice-Chancellor for Research and Technology at Mashhad University of Medical Sciences and to the Optometry and Paraclinical Department of Al-Zahra Ophthalmology Hospital for their cooperation in the implementation of this study.
Key Message: Corneal topographic and thickness measurements obtained with ACE showed good agreement with Pentacam, indicating their interchangeability. However, other variables measured by ACE did not demonstrate good agreement with either Pentacam or Orbscan, and thus are not interchangeable.
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Validad M, Shafiee H, Mahjoob M, Rakhshandadi T, Ostadimoghaddam H, Yekta A, et al . Evaluation of the Agreement of Advanced Corneal Explorer with Pentacam and Orbscan in Myopic Individuals with Healthy Corneas. J Gorgan Univ Med Sci 2025; 27 (2) :50-60 URL: http://goums.ac.ir/journal/article-1-4564-en.html
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