The Orbscan Acoustic (Correction) Factor for Central Corneal Thickness Measures of Normal Human Corneas

Doughty, Michael J.; Jonuscheit, Sven

doi:10.1097/icl.0b013e3181d0b604

Cited by 31 publications

(16 citation statements)

References 53 publications

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“…Doughty and Jonuscheit18 performed a meta-analysis of 46 studies evaluating Orbscan measurements with and without the correction factor; results showed that Orbscan may yield CCT measurement which is approximately 7% higher than US pachymetry. Some studies have suggested that universal use of correction factor of 0.92 may be inaccurate, and CCT measurements with Orbscan should be reported without any adjustment factor 13–15,18. This discrepancy between studies may be due to the fact that Orbscan measures thickness between air-tear interface and posterior corneal surface.…”

Section: Discussionmentioning

confidence: 99%

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan

Khaja

Grover

Kelmenson

et al. 2015

OPTH

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BackgroundCentral corneal thickness (CCT) can be measured by using contact and non-contact methods. Ultrasound pachymetry (US pachymetry) is a contact method for measuring CCT and is perhaps the most commonly used method. However, non-contact methods like scanning slit topography (Orbscan II), slit-lamp optical coherence tomography (SL-OCT), and specular microscopy are also used. Not many studies have correlated the measurement of CCT with all four modalities. The purpose of this study was to compare and correlate the CCT measurements obtained by US pachymetry with SL-OCT, specular microscopy, and Orbscan.MethodThis is a prospective, comparative study done in an institutional setting. Thirty-two eyes of 32 subjects with no known ocular disease and best-corrected visual acuity of 20/20 were enrolled. CCT measurements were obtained using SL-OCT, specular microscopy, scanning slit topography (Orbscan), and US pachymetry. Three measurements were made with each instrument by the same operator. Mean, standard deviation, and coefficient of variation were calculated for CCT measurements acquired by the four measurement devices. Bland–Altman plot was constructed to determine the agreements between the CCT measurements obtained by different equipment.ResultsThe mean CCT was 548.16±48.68 μm by US pachymetry. In comparison, CCT averaged 546.36±44.17 μm by SL-OCT, 557.61±49.92 μm by specular microscopy, and 551.03±48.96 μm by Orbscan for all subjects. Measurements by the various modalities were strongly correlated. Correlations (r2) of CCT, as measured by US pachymetry compared with other modalities, were: SL-OCT (r2=0.98, P<0.0001), specular microscopy (r2=0.98, P<0.0001), and Orbscan (r2=0.96, P<0.0001). All modalities had a linear correlation with US pachymetry measurements.ConclusionIn subjects with healthy corneas, SL-OCT, specular microscopy, and Orbscan (with correction factor) can be used interchangeably with US pachymetry in certain clinical settings. The four modalities showed significant linear correlations with one another.

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Section: Discussionmentioning

confidence: 99%

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan

Khaja

Grover

Kelmenson

et al. 2015

OPTH

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“…The CCT may decrease with increasing age [25], and female sex has also been associated with lower CCT [17]. The Orbscan system may overestimate CCT value as compared to the ultrasound pachymeter [22].…”

Section: Discussionmentioning

confidence: 99%

Correlation between central corneal thickness and myopia in Taiwan

Chen

Kasuga

Lee

et al. 2013

The Kaohsiung J of Med Scie

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The aim of the study was to explore the correlation between central corneal thickness (CCT) and the degree of myopia in Taiwanese adults. A total of 528 individuals were enrolled to undergo myopic laser refractive surgery from January 2004 to December 2006. Preoperative CCT was measured using the Orbscan corneal topography system and refractive status was determined by cycloplegic spherical equivalent. The relationship between CCT and refractive error was investigated by interindividual and intraindividual analyses. Participants had a mean age of 34.8 ± 7.3 years, and 79.9% were female. The mean refractive error was -7.27 ± 2.96 diopters and the mean CCT measurement was 560 ± 35 μm. CCT revealed that there was no association with age. However, CCT was significantly (p = 0.012) less in females than in males. The CCT also showed no significant association with refractive error (p = 0.49). Among the 67 participants with myopic anisometropia, the mean difference between both eyes was 3.09 ± 1.06 diopters. There was no association between the intereye CCT difference and refractive error (p = 0.57). The results remained the same after adjusting for age and sex. In conclusion, there was no correlation between CCT and the degree of myopia among adults in Taiwan. These data might contribute to the ongoing discussion about the role of CCT in the higher incidence of development and progression of glaucoma in myopic individuals.

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“…As expected, AFs minimize the mean difference between two methods,[11] but for the extremes of CCT this may lead to over or under estimation (which represents the effect of absolute CCT on degree of inter-device agreement). Indeed, correcting CCT readings in the thin range of CCT with a correction factor which is appropriate for thicker corneas would lead to underestimations.…”

Section: Introductionmentioning

confidence: 83%

“…This logical deduction was supported by our observation in this study as well as previous reports. In a review of 47 studies, Doughty and Joncheit [11] concluded “the global application of a 0.92 AF does not robustly align the Orbscan CCT data to that of the US pachymetry and; in fact, can easily result in the data being as much as 7% lower.”…”

Section: Discussionmentioning

confidence: 99%

Central corneal thickness measurement using ultrasonic pachymetry, rotating scheimpflug camera, and scanning-slit topography exclusively in thin non-keratoconic corneas

Mohammadpour¹,

Mohammad²,

Karimi³

2016

J Ophthalmic Vis Res

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Purpose:To evaluate the agreement among Pentacam, Orbscan and ultrasound (US) pachymetry for measurement of central corneal thickness (CCT) in thin corneas with normal topographic pattern.Methods:We included 88 eyes of 44 refractive surgery candidates with thinnest pachymetric readings of 500 micrometers (μm) or less on Orbscan, a normal topographic pattern, no sign of keratoconus, and best corrected visual acuity (BCVA) of 20/20. Pentacam, Orbscan and US were performed in one session by the same examiner. Exclusion criteria were history of ocular surgery, topographic abnormalities suggesting forme fruste keratoconus or keratectasia, and recent contact lens wear.Results:The difference in CCT measurements by US pachymetry and Orbscan II [using an acoustic factor (AF) of 0.92] ranged from −34 to +34 μm. The difference between the thinnest point and central readings measured by US reached 16 μm with Orbscan II (AF: 0.92) and 2 μm with Pentacam. Mean differences between the employed devices were 0.2 μm for Pentacam versus US (P = 0.727), 30.1 μm for uncorrected Orbscan versus US (P < 0.001), 10.4 μm for Orbscan II (AF = 0.92) versus US (P < 0.001), and 0.2 μm for Orbscan II (AF = 0.94) versus US (P = 0.851).Conclusion:In normal thin corneas, Pentacam demonstrated better agreement with US pachymetry as compared to corrected Orbscan readings. Results achieved by Orbscan were better consistent with US pachymetry using an AF of 0.94. We speculate that a dynamically graded AF in reverse proportion to CCT constitutes a better approach for correcting Orbscan measurements.

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The Orbscan Acoustic (Correction) Factor for Central Corneal Thickness Measures of Normal Human Corneas

Cited by 31 publications

References 53 publications

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan

Correlation between central corneal thickness and myopia in Taiwan

Central corneal thickness measurement using ultrasonic pachymetry, rotating scheimpflug camera, and scanning-slit topography exclusively in thin non-keratoconic corneas

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The Orbscan Acoustic (Correction) Factor for Central Corneal Thickness Measures of Normal Human Corneas

Cited by 31 publications

References 53 publications

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and&nbsp;Orbscan

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and&nbsp;Orbscan

Correlation between central corneal thickness and myopia in Taiwan

Central corneal thickness measurement using ultrasonic pachymetry, rotating scheimpflug camera, and scanning-slit topography exclusively in thin non-keratoconic corneas

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Product

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Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan