Agreement between the Orbscan II, VuMAX UBM and Artemis-2 very-high frequency ultrasound scanner for the measurement of anterior chamber depth.
Journal Article
Al-Farhan, Haya . 2014
نوع عمل المنشور:
article
رابط المنشور على الويب:
المجلة \ الصحيفة:
BMC Ophthalmol
رقم الإصدار السنوي:
14
الصفحات:
20-27
مستخلص المنشور:
Background
The aim was to compare the anterior chamber depth (ACD) measurements taken with Orbscan II, ultrasound biomicroscopy (UBM) and the Artemis-2 VHF (very-high-frequency) ultrasound scanner in normal subjects.
Methods
In this prospective study, one eye from each of 60 normal subjects was randomly selected. Three subjects dropped out of the study because they were apprehensive about the UBM examination; their data were excluded entirely. Measurements of ACD were taken with the Orbscan II, UBM and Artemis-2 VHFUS. Results were obtained for coefficient of variance (CV) and intra-class correlation coefficient (ICC), and statistical analysis was by repeated-measures analysis of variance (ANOVA) for intra-observer repeatability. ANOVA and Bland–Altman analyses were used to determine limits of agreement (LOA) between the three instruments.
Results
The average ACD (± standard deviation) was 3.13 ± 0.34 mm, 2.96 ± 0.27 mm and 2.87 ± 0.31 mm for the Orbscan II, UBM and Artemis-2 VHFUS, respectively. The repeatability scores were 0.015 ± 0.014%, 0.08 ± 0.09% and 0.07 ± 0.06% for the Orbscan II, UBM and Artemis-2 VHFUS, respectively. The ICC for repeatability of Orbscan II, UBM and Artemis-2 VHFUS measurements was high and equal to 0.99%. The intra-observer repeatability scores of the ACD measurement p-values using Orbscan II, UBM and Artemis-2 VHFUS were 0.12, 0.70 and 0.10, respectively. The mean difference and standard deviations for ACD measurements using Orbscan II vs UBM, Orbscan II vs Artemis-2 VHFUS and UBM vs Artemis-2 VHFUS were 0.17 ± 0.31 mm, 0.27 ± 0.34 mm and 0.10 ± 0.18 mm, respectively. LOAs were 0.78 to -0.44 mm, 0.93 to -0.39 mm and 0.45 to -0.26 mm. ANOVA revealed a statistically significant difference between the Orbscan II, UBM and Artemis-2 VHFUS (p < 0.0001).
Conclusions
Measurements by the three instruments show high repeatability. UBM and the Artemis-2 VHFUS can be used interchangeably, but the Orbscan II cannot be used interchangeably with UBM or the Artemis-2 VHFUS.
Keywords: Anterior chamber depth, Artemis-2 VHF, Normal eyes, Orbscan II, Ultrasound biomicroscopy, Ultrasound scanner
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Background
It is well-documented that anterior chamber depth (ACD) measurement is essential as a screening method for primary angle-closure glaucoma [1,2]; it is also used in biometry to calculate the power of intraocular lenses (IOLs) [3], for determining the precise optic zone ablation diameter in keratorefractive surgery [4], and in postoperative assessments [5].
Recently, new techniques have been introduced to assess ACD using either ultrasonic or optical technologies [6]. Ultrasonic immersion instruments include the ultrasound biomicroscope (UBM; Sonomed Inc., New York, USA) [7-9] and the Artemis-2 VHFUS scanner (Scott Philips Engineering, Victoria, BC, Canada) [10]. Optical methods that have been studied include anterior segment optical coherence tomography (OCT) [11] and Scheimpflug imaging [12].
Ultrasound and optical techniques allow quantitative measurements of ACD. Optical methods are objective, however it is difficult to accurately measure ACD in the presence of edema, opacities, scarring or deposits in the optical media [12]. In contrast, ultrasound-based methods do not require clear optical media to obtain precise measurements of ACD. There are disadvantages of UBM: for example, the examiner must manually adjust the transducer head to maximize centrality and perpendicularity of the image, which takes time, and analog-based UBM does not image the interface consistently because analog processing does not produce a high enough signal-to-noise ratio between the interface echo complex and the surrounding tissue [13].
Previous studies have investigated the agreement between ACD measurements obtained with these different instruments [7-13] but, to the best of our knowledge, this is the first study to compare measurements obtained with these devices in normal eyes. The aim of this study was to assess the repeatability and agreement of ACD measurements obtained using the Orbscan II topography system, UBM and the Artemis-2 VHFUS.
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