|Year : 2023 | Volume
| Issue : 1 | Page : 10-14
Comparison of central corneal thickness measurements obtained by OrbscanIIz® and ultrasound pachymetry: A concordance study in the usual clinical practice
Josť L Romero-Trevejo1, Andrés Sánchez-Pérez2, Erika Muñoz-García2, Lourdes Fernández-Romero3, Manuel F Jiménez-Navarro4
1 Department of Ophthalmology, Virgen de la Victoria University Hospital; Department of Medicine and Dermatology, School of Medicine, University of Malaga, Malaga, Spain
2 Department of Heart and Cardiovascular Pathology, Virgen de la Victoria University Hospital, Malaga, Spain
3 Malaga Biomedical Research Institute-IBIMA, Virgen de la Victoria University Hospital, Malaga, Spain
4 Department of Medicine and Dermatology, School of Medicine, University of Malaga; Department of Heart and Cardiovascular Pathology, Virgen de la Victoria University Hospital; Malaga Biomedical Research Institute-IBIMA, Virgen de la Victoria University Hospital, Malaga; CIBERCV Cardiovascular Diseases, Carlos III Health Institute, Madrid, Spain
|Date of Submission||10-Apr-2021|
|Date of Decision||01-Jun-2022|
|Date of Acceptance||01-Feb-2023|
|Date of Web Publication||09-Mar-2023|
Josť L Romero-Trevejo
Department of Ophthalmology, Virgen de la Victoria University Hospital, Campus de Teatinos, S/n. 29010, Malaga
Source of Support: None, Conflict of Interest: None
PURPOSE: The objective of this study was to assess the concordance between the values obtained in measuring central corneal thickness using the OrbscanIIz® and the contact ultrasonic pachymeter available in our public ophthalmology service.
METHODS: Measurements were taken from 88 eyes of 44 patients using the two instruments. The data obtained were statistically analyzed using version 22 of the IBM SPSS® program.
RESULTS: The mean of central corneal thickness measurements obtained from OrbscanIIz® was significantly higher than that obtained from ultrasound pachymetry. However, the mean of differences between both instruments was only 7.22 μ, which could be considered a clinically insignificant result when considering the good concordance obtained between both systems.
CONCLUSION: OrbscanIIz® and ultrasound pachymetry can be interchangeable in the usual public clinical practice when measuring central corneal thickness. This is the first research found in the literature that uses a concordance study to compare the data resulting from central corneal thickness measurements obtained by an OrbscanIIz® and an OcuScan® pachymeter in our environment.
Keywords: Bland–Altman plot, central corneal thickness, concordance, corneal topography, ultrasound pachymetry
|How to cite this article:|
Romero-Trevejo JL, Sánchez-Pérez A, Muñoz-García E, Fernández-Romero L, Jiménez-Navarro MF. Comparison of central corneal thickness measurements obtained by OrbscanIIz® and ultrasound pachymetry: A concordance study in the usual clinical practice. Saudi J Ophthalmol 2023;37:10-4
|How to cite this URL:|
Romero-Trevejo JL, Sánchez-Pérez A, Muñoz-García E, Fernández-Romero L, Jiménez-Navarro MF. Comparison of central corneal thickness measurements obtained by OrbscanIIz® and ultrasound pachymetry: A concordance study in the usual clinical practice. Saudi J Ophthalmol [serial online] 2023 [cited 2023 Mar 24];37:10-4. Available from: https://www.saudijophthalmol.org/text.asp?2023/37/1/10/371396
| Introduction|| |
Central corneal thickness is an important and sensitive indicator when evaluating the state of corneal health. It is useful when tracking alterations such as corneal edema or keratoconus when selecting patients who may be candidates for refractive surgery, and in the assessment of the effects of contact lens use or treatments for dry eye.,,,, In addition, central corneal thickness is a known significant risk factor for the progression from ocular hypertension to glaucoma. It is well established that a thinner central corneal thickness is related to a more severe glaucomatous defect,,,,,, and that this characteristic constitutes an independent risk factor for the development of primary open-angle glaucoma. For these reasons, in the usual clinical practice, it is essential that reliable measurement values of central corneal thickness be obtained for this type of patient. However, this task is not always easy given the increasing availability of devices that measure this parameter and the subsequent doubts that may arise about concordance between the data obtained from them. During the last years, many studies have been found in the literature concerning the comparison of central corneal thickness measurement between different devices, although not always the correct statistical tools were applied to ascertain their concordance.
| Methods|| |
In order to assess the concordance between measurements obtained from the two instruments available in our public service, and after obtaining approval of the regional ethics committee following the tenets of the Declaration of Helsinki, and the written informed consent of each patient, we conducted a comparative, cross-sectional observational study of measurements of central corneal thickness. First, to ensure that corneal integrity was not compromised by the ultrasound probe or due to variations in the tear film, the central corneal thickness was measured with the slit scanning technology of OrbscanIIz® (Bausch and Lomb), using an acoustic adjustment factor of 0.92. Subsequently, after administering oxybuprocaine anesthetic eye drops, measurements were taken using contact ultrasound pachymetry with the OcuScan® (Alcon). To minimize technical errors and diurnal fluctuations, all measurements were taken by the same operator, experienced in using both instruments, at the same time of day (between 3 pm and 5 pm), with a time interval of approximately 5 min between each measurement. The data obtained were analyzed using version 22 of the IBM SPSS® program (Armonk, NY, USA), where a paired Student's t-test was used to compare them. The right and left eyes were compared separately and together, and the results were expressed as a mean ± standard deviation, taking a value of P ≤ 0.05 as statistically significant. To assess concordance between the two measurement methods employed, Bland–Altman plots were constructed, assuming confidence intervals (CIs) of 95%. This technique allows a swift assessment of the prediction capacity of one test compared to another established one, being more appropriate than correlation coefficients.
| Results|| |
Measurements of central corneal thickness were obtained for 88 eyes of 44 patients (38 men and 6 women) with a mean age of 58.61 ± 9.43 years (ranging between 42 and 77 years) with no prior corneal pathology detected with the slit lamp and no prior related surgery. Obtained data are summarized in [Table 1].
|Table 1: Mean central corneal thickness measurements obtained by OrbscanIIz® and OcuScan®|
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The mean central corneal thickness of the right eyes obtained using OrbscanIIz® and ultrasound pachymetry was 556.32 ± 34.19 μ and 549.34 ± 32.01 μ respectively. These results show that the values obtained using OrbscanIIz® were a mean of 6.98 μ higher than those of ultrasound pachymetry, which constituted a statistically significant difference (P = 0.004). The Bland–Altman plot confirmed this result, giving a mean of differences of 6.98 μ, with CIs of 95% from 2.4 to 11.56 μ [Figure 1].
|Figure 1: Box plot showing quartile distribution of data for the right eye. Bland–Altman plot showing the homogeneous distribution of data around the mean of differences axis for the right eye|
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The mean central corneal thickness of left eyes obtained using OrbscanIIz® and ultrasound pachymetry was 555.93 ± 31.71 μ, and 548.48 ± 31.51 μ respectively. These results show that the values obtained using OrbscanIIz® were a mean of 7.45 μ higher than those of ultrasound pachymetry, which likewise constituted a statistically significant difference (P = 0.006). The Bland–Altman plot confirmed this result, giving a mean of differences of 7.45 μ, with CIs of 95% from 2.22 to 12.69 μ [Figure 2].
|Figure 2: Box plot showing quartile distribution of data for the left eye. Bland–Altman plot showing the homogeneous distribution of data around the mean of differences axis for the left eye|
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Expressed together, the mean central corneal thickness for both eyes obtained using OrbscanIIz® and ultrasound pachymetry was 556.12 ± 32.79 μ and 548.91 ± 31.58 μ, respectively. These results show that the values obtained using OrbscanIIz® were a mean of 7.22 μ higher than those of ultrasound pachymetry, which constituted a statistically significant difference (P < 0.001). The Bland–Altman plot again confirmed this result, giving a mean of differences of 7.22 μ, with CIs of 95% from 3.81 to 10.63 μ [Figure 3].
|Figure 3: Box plot showing quartile distribution of data for both eyes together. Bland–Altman plot showing the homogeneous distribution of data around the mean of differences axis for both eyes together|
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| Discussion|| |
Central corneal thickness is a frequently measured parameter in the usual clinical practice, and there are numerous methods available to ascertain it. The method currently considered the gold standard is ultrasound pachymetry, due to its simplicity, speed, good repeatability, and reproducibility,,,,, despite being a highly operator-dependent procedure that requires direct contact of the probe with the ocular surface. This may interfere with the measurement due to displacement of the tear film that accompanies compression of the cornea, residue of the anesthetic drops, or the transitory edema that is produced when administering them. To avoid these problems, numerous devices have been developed recently that can measure, among other parameters, central corneal thickness by means of noninvasive techniques and which are based on principles of physics other than ultrasound. Nevertheless, the studies published to date have not clarified whether the results obtained from these different devices are interchangeable in the usual clinical practice,,,,,,,, and very few studies in our environment compare their concordance using Bland–Altman plots, the most correct statistical tool available to assess it.
The results obtained in our study, which, for the first time, compares two of the most frequently available and most commonly used devices in the usual public clinical practice in our region, show that the mean of central corneal thickness measurements was significantly higher using OrbscanIIz® than ultrasound pachymetry, whether both eyes were analyzed individually or together. This fact could be due to the above-mentioned consequences of employing a contact method such as the latter device on the cornea, where the pressure of the probe on the corneal surface could produce abnormally decreased values. This data is congruent with a previously published study, which concluded that optical devices might overestimate the measurement of central corneal thickness when compared to ultrasound pachymetry, among other methods. However, it has also been documented that lower values are obtained with optical devices than with ultrasound pachymetry, so the results found related to this question to date do not seem consistent.
Considering comparisons between instruments other than those employed in our study, some research has indicated that the measurement of central corneal thickness using ultrasound pachymetry gives higher values than anterior segment optical coherence tomography (AS-OCT),,,, and that the measurements obtained from the two devices are not interchangeable in the usual clinical practice for this purpose,,, despite the well correlation of the measurements obtained., Other studies, on the contrary, highlight the high agreement between the two. On the other hand, other published literature indicates that, in general, technologies based on OCT may overestimate central corneal thickness value compared with ultrasound pachymetry. Moreover, both Tonoref III® (Nidek) and RS-3000® (Nidek) give values lower than those of ultrasound pachymetry, with results that are not directly interchangeable in the usual clinical practice. The same occurs in a comparison between Placido disc-based keratoscopy and Scheimpflug tomography, between Pentacam AXL® (Oculus) and CASIA 2® (Tomey), or when comparing IOL Master 700® (Zeiss) and the specular microscope EM-3000® (Tomey), where interchangeability between these methods in clinical practice resulted limited. The devices used in these last studies were not compared with the gold standard ultrasound pachymetry. However, other studies concluded that optical biometer devices, but not Galilei® (Imex), could be an alternative to ultrasound pachymetry for measurement of central corneal thickness, and that noncontact pachymeter as TRK-2P® (Topcon) and optical low coherence reflectometer as Lenstar LS-900® (Haag-Streit) showed an excellent agreement when evaluating healthy corneas.
Focusing on nonhealthy corneas, a recent study compared ultrasound pachymetry and optical measurement with the specular microsope CEM-530® (Nidek) in healthy and glaucoma patients. The conclusion was that both devices could be used interchangeably in older and glaucoma patients, but not in young individuals, due to changes in corneal biomechanical properties between these groups of patients. Otherwise, Galilei® and Pentacam® were not interchangeable for post-LASIK evaluation, as data obtained were not identical when assessing these patients. In corneal edema, ultrasound pachymetry, Pentacam® and AS-OCT were able to reach a high level of agreement in higher degrees of disease, but significant differences were found when patients with lower degrees of corneal edema where measured.
The existence of such discrepancies among the different studies is indicative of their methodological diversity, and in terms of clinical practice represents an enormous difficulty when selecting the most reliable method for measuring central corneal thickness. In our case, the mean difference between the devices employed was only 7.22 μ, and there was good concordance between both methods for the proposed CIs. Therefore, the clinical importance of this fact could be insignificant, and the choice of one or other method when conducting reliable, accurate measurements of central corneal thickness for patients who require it should be at the examiner's discretion. Ease of use or obtaining other types of parameter unrelated with central corneal thickness could constitute arguments of or against the preferential use of one device over the other.
Limitations of our study were the small number of patient sample size as well as the small range of age used. More studies are required to determine if these results are consistent and reliable when the general population or nonhealthy corneas are employed.
| Conclusion|| |
OrbscanIIz® and ultrasound pachymetry can be interchangeable in the usual public clinical practice when measuring central corneal thickness. The choice of one or other method should be at the examiner's discretion.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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