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      Comparison of central corneal thickness and anterior chamber depth measurements using three imaging technologies in normal eyes and after phakic intraocular lens implantation

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          Abstract

          Background

          The repeatability and interchangeability of imaging devices measuring central corneal thickness (CCT) and anterior chamber depth (ACD) are important in the assessment of patients considering refractive surgery. The purpose of this study was to investigate the agreement of CCT and ACD measurements using three imaging technologies in healthy eyes and in eyes after phakic intraocular lens implantation (pIOL).

          Methods

          In this comparative study, CCT and ACD were measured using anterior segment optical coherence tomography (AS-OCT), Orbscan II, and Pentacam in 33 healthy volunteers (66 eyes) and 22 patients (42 eyes) after pIOL implantation. Intraobserver repeatability was evaluated for all three devices in the healthy volunteer group.

          Results

          Pairwise comparison of CCT measurements showed significant differences between all devices ( P < 0.001), except for the AS-OCT and Orbscan II in the healthy volunteer group ( P = 0.422) and the Orbscan II and Pentacam in the pIOL group ( P = 0.214). ACD measurements demonstrated significant differences between all pairwise comparisons in both groups ( P ≤ 0.001). Intraobserver reliability was high for CCT and ACD measurements in the healthy volunteer group, with coefficients of variation ranging from 0.6% to 1.2% and 0.4% to 0.5% respectively.

          Conclusions

          CCT and ACD measurements using AS-OCT, Orbscan II, and Pentacam demonstrated high intraobserver reliability. However, these devices should not be used interchangeably for measurements of CCT and ACD in healthy subject and patients after pIOL implantation.

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          Most cited references21

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          Statistical methods for assessing agreement between two methods of clinical measurement.

          In clinical measurement comparison of a new measurement technique with an established one is often needed to see whether they agree sufficiently for the new to replace the old. Such investigations are often analysed inappropriately, notably by using correlation coefficients. The use of correlation is misleading. An alternative approach, based on graphical techniques and simple calculations, is described, together with the relation between this analysis and the assessment of repeatability.
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            Repeatability and reproducibility of central corneal thickness measurement with Pentacam, Orbscan, and ultrasound.

            The purpose of this study was to compare central corneal thickness (CCT) measurements obtained with a novel rotating Scheimpflug camera (Pentacam; Oculus) with scanning slit topography (Orbscan; Bausch & Lomb), and with ultrasound pachymetry (SP-2000; Tomey). CCT in 30 healthy eyes was measured twice with each modality by 2 independent observers in random order. The results from scanning slit topography are given both with and without multiplication with the "acoustic correction factor" of 0.92. In addition, the displayed images from the rotating Scheimpflug camera and scanning slit topography were used to calculate the signal difference-to-noise ratios (SD/N) between cornea and background signal. The mean CCT values as determined with the different modalities (+/-standard deviation) were: 542+/-29 microm, 576+/-37 microm, 530+/-34 microm, and 552+/-32 microm for rotating Scheimpflug imaging, for uncorrected and for corrected scanning slit pachymetry, and for ultrasound, respectively. The differences between modalities (+/-95% limits of agreement) were -9.8+/-31 microm between rotating Scheimpflug and ultrasound, 24+/-31.2 microm between scanning slit and ultrasound, and 33+/-27 microm between scanning slit and rotating Scheimpflug imaging. The limits of agreement for within and between observer effects were within 4.2% of the absolute CCT values for scanning slit and ultrasound and within 2.2% for the rotating Scheimpflug imaging. The rotating Scheimpflug camera showed similar SD/N ratios but steeper edges of the corneal surfaces in the intensity profile plots. In the assessment of normal corneas, the Pentacam measured CCT values closer to ultrasound pachymetry and with less variability compared with Orbscan. The (interobserver) reproducibility with the Pentacam was highest of all 3 modalities.
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              Evaluation of corneal thickness and topography in normal eyes using the Orbscan corneal topography system.

              To map the thickness, elevation (anterior and posterior corneal surface), and axial curvature of the cornea in normal eyes with the Orbscan corneal topography system. 94 eyes of 51 normal subjects were investigated using the Orbscan corneal topography system. The anterior and posterior corneal elevation maps were classified into regular ridge, irregular ridge, incomplete ridge, island, and unclassified patterns, and the axial power maps were grouped into round, oval, symmetric bow tie, asymmetric bow tie, and irregular patterns. The pachymetry patterns were designated as round, oval, decentred round, and decentred oval. The thinnest point on the cornea was located at an average of 0.90 (SD 0. 51) mm from visual axis and had an average thickness of 0.55 (0.03) mm. In 69.57% of eyes, this point was located in the inferotemporal quadrant, followed by the superotemporal quadrant in 23.91%, the inferonasal quadrant in 4.35%, and the superonasal quadrant in 2.17%. Among the nine regions of the cornea evaluated (central, superotemporal, temporal, inferotemporal, inferior, inferonasal, nasal, superonasal, and superior) the central cornea had the lowest average thickness (0.56 (0.03) mm) and the superior cornea had the greatest average thickness (0.64 (0.03) mm). The mean simulated keratometry (SimK) was 44.24 (1.61)/43.31 (1.66) dioptres (D) and the mean astigmatism was 0.90 (0.41) D. Island (71.74%) was the most common elevation pattern observed in the anterior corneal surface, followed by incomplete ridge (19.57%), regular ridge (4.34%), irregular ridge (2.17%), and unclassified (2.17%). Island (32.61%) was the most common topographic pattern in the posterior corneal surface, following by regular ridge (30.43%), incomplete ridge (23. 91%), and irregular ridge (13.04%) patterns. Symmetric bow tie was the most common axial power pattern in the anterior cornea (39.13%), followed by oval (26.07%), asymmetric bow tie (23.91%), round (6. 52%), and irregular (4.53%) patterns. In the pachymetry maps, 47.83% of eyes had an oval pattern, and round, decentred oval, and decentred round were observed in 41.30%, 8.70%, and 2.18% of eyes, respectively. The information on regional corneal thickness, corneal elevation and axial corneal curvature obtained with the Orbscan corneal topography system from normal eyes provides a reference for comparison with diseased corneas. The Orbscan corneal topography system is a useful tool to evaluate both corneal topography and corneal thickness.
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                Author and article information

                Contributors
                +31-43-3877346 , +31-43-3875343 , rudy.nuijts@mumc.nl
                Journal
                Graefes Arch Clin Exp Ophthalmol
                Graefe's Archive for Clinical and Experimental Ophthalmology
                Springer-Verlag (Berlin/Heidelberg )
                0721-832X
                1435-702X
                30 April 2009
                August 2009
                : 247
                : 8
                : 1139-1146
                Affiliations
                Department of Ophthalmology, University Hospital Maastricht, P. Debyelaan 25, 6202 AZ Maastricht, The Netherlands
                Article
                1086
                10.1007/s00417-009-1086-6
                2709228
                19404662
                c597ee5b-90f5-4ae6-98e0-b24a23577c06
                © The Author(s) 2009
                History
                : 24 October 2008
                : 23 March 2009
                : 6 April 2009
                Categories
                Refractive Surgery
                Custom metadata
                © Springer-Verlag 2009

                Ophthalmology & Optometry
                phakic intraocular lens,anterior segment imaging,anterior chamber depth,corneal thickness,optical coherence tomography

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