Central corneal thickness measured by the Orbscan II system, contact ultrasound pachymetry, and the Artemis 2 system

Abstract

Purpose-To compare central corneal thickness measurements obtained by Orbscan II, contact ultrasound pachymetry and the non-contact Artemis-2 scanning ultrasound system. Methods-The central corneal thickness of 40 eyes (20 normal subjects) was measured using first the Orbscan II, followed by contact ultrasound pachymetry, and finally by the Artemis-2. Results were compared statistically using ANOVA, paired T-tests, and Bland-Altman plots.Results-One-way ANOVA showed a significant difference between the three different modes of measuring central corneal thickness (F=32.84, p=0.0001). Artemis-2 and the ultrasound pachymeter measurements were highly correlated (R 2 =0.963, p<0.0001), but with Artemis, on average, measuring central corneal thickness by 11.2±6.6 microns less than the pachymeter. The Artemis-2 and Orbscan II measurements were less well correlated (R 2 =0.851, p<0.001), with Orbscan measurements on average 7.5±15.7 microns thinner than those obtained with the Artemis-2. In addition, the Orbscan showed a trend towards increasing underestimation of corneal thickness for thinner corneas.Conclusions-Ultrasound pachymetry and Artemis-2 measurements of central corneal thickness were highly correlated. The 11-micron mean difference between the pachymeter and Artemis measurements may be attributed to decentration, oblique incidence of the probe to the cornea or possibly the effect of topical anesthetic when using contact pachymetry. While Orbscan values only had an average difference of 7.5 microns from Artemis, they were less correlated than contact ultrasound pachymetry with Artemis values and increasing prone to underestimation of corneal thickness for thinner corneas.

Comparison of Artemis 2 Ultrasound and Visante Optical Coherence Tomography Corneal Thickness Profiles

“…We found Visante OCT CCT to average 8 μm thinner than Artemis 2 immersion high-frequency ultrasound. Paul et al 17 found Artemis 2 CCT values to average 11 μm thinner than USP, which, together with the 8-μm difference observed in our present study, suggests an expected difference between Visante and USP of ~19 μm. This is comparable to differences, averaging ~15 μm, reported in several studies comparing USP with Visante.…”

Measurement of central corneal thickness by high‐resolution Scheimpflug imaging, Fourier‐domain optical coherence tomography and ultrasound pachymetry

“…There are several theoretical explanations for the discrepancy between both optical methods and UP in measuring the CCT. These include decentration, oblique incidence of the probe to the cornea, possible effect of topical anaesthesia with contact pachymetry and the variability of ultrasound speed in tissues of different hydration (Gonzalez-Meijome et al 2003;Nemeth et al 2006;Paul et al 2008). The accuracy of UP is operator dependent.…”

Repeatability and interobserver reproducibility of Artemis-2 high-frequency ultrasound in determination of human corneal thickness

“…In an earlier study3 comparing Artemis-2 CCT measurements with those of a hand-held ultrasound pachymeter, the Artemis-2 measured significant thinner (11 μm) CCT values when compared with ultrasound pachymetry in normal subjects. This could be due to the fact that our sample was more homogeneous considering the ages of the subjects and, as such, less prone to variations.…”

“…Accurate measurement of CCT with the hand-held ultrasound pachymeter relies on placement of the probe as close as possible to the central cornea. Higher values will be obtained if the probe is not placed at 90 degrees to the corneal surface or if placed slightly off center 3. With hand-held ultrasound pachymetry, the same place on the cornea is not measured on every occasion, and because the cornea varies in thickness according to location, this adds to some error.…”