Corneal pachymetry in normal and keratoconic eyes: Orbscan II versus ultrasound.
ABSTRACT To compare corneal thickness measurements using Orbscan II (OII) and ultrasonic (US) pachymetry in normal and in keratoconic eyes.
Eye Department, Heartlands and Solihull NHS Trust, Birmingham, United Kingdom.
Central corneal thickness (CCT) was measured by means of OII and US pachymetry in 1 eye of 72 normal subjects and 36 keratoconus patients. The apical corneal thickness (ACT) in keratoconus patients was also evaluated using each method. The mean of the difference, standard deviation (SD), and 95% limits of agreement (LoA = mean +/- 2 SD), with and without applying the default linear correction factor (LCF), were determined for each sample. The Student t test was used to identify significant differences between methods, and the correlation between methods was determined using the Pearson bivariate correlation. Bland-Altman analysis was performed to confirm that the results of the 2 instruments were clinically comparable.
In normal eyes, the mean difference (+/- 95% LoA) in CCT was 1.04 microm +/- 68.52 (SD) (P>.05; r = 0.71) when the LCF was used and 46.73 +/- 75.40 microm (P =.0001; r = 0.71) without the LCF. In keratoconus patients, the mean difference (+/- 95% LoA) in CCT between methods was 42.46 +/- 66.56 microm (P<.0001: r = 0.85) with the LCF, and 2.51 +/- 73.00 microm (P>.05: r = 0.85) without the LCF. The mean difference (+/- 95% LoA) in ACT for this group was 49.24 +/- 60.88 microm (P<.0001: r = 0.89) with the LCF and 12.71 +/- 68.14 microm (P =.0077; r = 0.89) when the LCF was not used.
This study suggests that OII and US pachymetry provide similar readings for CCT in normal subjects when an LCF is used. In keratoconus patients, OII provides a valid clinical tool for the noninvasive assessment of CCT when the LCF is not applied.
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ABSTRACT: To compare geometrical shape factors of keratoconus corneas after cross-linking (CXL) by means of Scheimpflug imaging with those of untreated fellow eyes. Institut für Refraktive und Ophthalmo-Chirurgie, Zürich, Switzerland. Scheimpflug imaging of the anterior segments was performed with the Pentacam (Oculus, Wetzlar, Germany) in 21 patients with progressive keratectasia before and after CXL. Only 1 eye per patient was treated with corneal cross-linking using the riboflavin/UV-A approach, the fellow eye serving as control. The following corneal parameters and their postoperative evolution during 1 year after treatment have been evaluated: minimal curvature radius and its location, thickness at the thinnest point, location of the thinnest point, anterior and posterior elevation, conoid asphericity constants of the anterior and posterior surface, and 7 keratoconus indices. Statistical comparison was performed by means of the Wilcoxon test. None of the treated eyes showed topographic progression in contrast to the untreated group where 8 eyes experienced significant progression. Minimal curvature radius increased significantly after 1 year compared with preoperative (6.14-6.21 mm), whereas in the untreated fellow eye, it significantly decreased (6.94-6.86 mm). Minimal corneal thickness was significantly reduced after treatment (P < 0.002 at 12 months). The cornea showed an evolution toward a more regular shape as indicated by a significant reduction in 4 of 7 keratoconus indices. No complications of CXL occurred in this small study group. After cross-linking, the corneal shape undergoes a process of regularization. This process is active during the first year after treatment and may continue. Longer follow-up is warranted to estimate the full amount of regression of the keratectasia after CXL.Cornea 04/2009; 28(5):510-5. · 1.73 Impact Factor
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ABSTRACT: To evaluate the effects of wearing rigid gas permeable (RGP) contact lenses on the topographic changes in keratoconus. Seventy-seven keratoconic eyes that wore multicurve RGP contact lenses and 30 keratoconic eyes that wore no contact lenses were retrospectively analyzed. The mean follow-ups were 22.6 and 20.5 months in the lens-wearing and control groups, respectively. Visual acuity, comfort, daily wearing time, and corneal staining were evaluated for both groups. The changes in topographic indices were compared between the lens-wearing and control groups. Multicurve RGP lens corrected logarithm of the minimum angle of resolution visual acuity of the lens-wearing group significantly improved from -0.016+/-0.065 to -0.032+/-0.10 at follow-up (p=0.05). In the lens-wearing group with advanced keratoconus, the Sim Kmax, Sim Kmin, apical power, astigmatic index, and anterior elevation significantly decreased from 57.68+/-4.26 diopter (D), 50.50+/-2.32 D, 62.79+/-5.11 D, 7.20+/-0.55 D and 67.36+/-16.30 microm to 55.51+/-4.28 D, 49.62+/-3.26 D, 60.31+/-5.41 D, 5.90+/-0.51 D and 60.61+/-16.09 microm, respectively (paired t-test, p<0.05). The irregularity index of 3 mm did not significantly change. Meanwhile, in the control group, the apical power and irregularity index increased from 55.56+/-7.25 D and 3.06+/-1.68 D to 57.11+/-7.75 D and 3.25+/-1.71 D, respectively (paired t-test, p=0.008, p=0.01). Properly fitted multicurve RGP contact lenses are not likely to contribute to the progression of keratoconus.Korean Journal of Ophthalmology 08/2010; 24(4):201-6.
Article: Comparison of central corneal thickness measurements using ultrasound pachymetry, ultrasound biomicroscopy, and the Artemis-2 VHF scanner in normal eyes.[show abstract] [hide abstract]
ABSTRACT: To compare the precision of central corneal thickness (CCT) measurements taken with the handheld ultrasound pachymeter (USP), ultrasound biomicroscopy (UBM), and the Artemis-2 very high frequency ultrasound scanner (VHFUS) on normal subjects. Prospective study. One eye from each of 61 normal subjects was randomly selected for this study. The measurements of the CCT were taken with the USP, VHFUS, and UBM. Results were compared statistically using repeated-measures analysis of variance (ANOVA), Pearson's correlation coefficient, and limits of agreement. The average CCT (± standard deviation) was 530.1 ± 30.5 μm, 554.9 ± 31.7 μm, and 559.5 ± 30.7 μm for UBM, VHFUS, and USP respectively. The intraobserver repeatability analyses of variance are not significant for USP, UBM, and VHFUS. P-values were 0.17, 0.19, and 0.37 respectively. Repeated-measures ANOVA showed a significant difference between the three different methods of measuring CCT (P = 0.0001). The ANOVA test revealed no statistically significant difference between USP and VHFUS (P > 0.05), yet statistical significant differences with UBM versus USP and UBM versus VHFUS (P < 0.001). There were high correlations between the three instruments (P < 0.0001). The mean differences (and upper/lower limits of agreement) for CCT measurements were 29.4 ± 14.3 (2.7/56), 4.6 ± 8.6 (-14.7/23.8), and -24.8 ± 13.1 (-50.4/0.8) for USP versus UBM, USP versus VHFUS, and UBM versus VHFUS, respectively. The UBM produces CCT measurements that vary significantly from those returned by the USP and the VHFUS, suggesting that the UBM may not be used interchangeably with either equipment for monitoring the CCT in the clinical setting.Clinical Ophthalmology 01/2012; 6:1037-43.