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

Tania Paul, Mira Lim, Christopher E Starr, Harriet O Lloyd, D Jackson Coleman, Ronald H Silverman, Tania Paul, Mira Lim, Christopher E Starr, Harriet O Lloyd, D Jackson Coleman, Ronald H Silverman

Abstract

Purpose: To compare central corneal thickness (CCT) measurements by the Orbscan II device, contact ultrasound (US) pachymetry, and the noncontact Artemis 2 scanning US system.

Setting: Department of Ophthalmology, Weill Cornell Medical College, New York, New York, USA.

Methods: The CCT in 40 eyes (20 normal subjects) was measured by the Orbscan II followed by contact US pachymetry and then the Artemis 2. Results were compared using analysis of variance (ANOVA), paired t tests, and Bland-Altman plots.

Results: There was a significant difference in CCT measurements between the 3 modes (F = 32.84, P = .0001, 1-way ANOVA). Artemis 2 and US pachymetry measurements were highly correlated (r2 = 0.963, P < .0001), although Artemis 2 values were a mean of 11.2 microm +/- 6.6 (SD) thinner than pachymetry values. Artemis 2 and Orbscan II measurements were less well correlated (r2 = 0.851, P < .001); Orbscan II values were a mean of 7.5 +/- 15.7 microm thinner than Artemis 2 values. Orbscan II values showed a trend toward increasing underestimation of CCT in thinner corneas.

Conclusions: Ultrasound pachymetry and Artemis 2 CCT measurements were highly correlated; the 11 microm mean difference in measurements may be attributed to decentration, oblique incidence of the probe to the cornea, or possibly the effect of topical anesthesia with contact pachymetry. Although the mean difference between Orbscan II and Artemis 2 values was 7.5 microm, Orbscan values were less correlated than Artemis 2 values with contact US pachymetry and were prone to underestimation of the CCT in thinner corneas.

Figures

Figure 1
Figure 1
Figure 1a. Contact ultrasound pachymeter versus Artemis-2 measurements of central corneal thickness. Figure 1b. Bland-Altman plot of the handheld US pachymeter compared with the Artemis-2. The horizontal lines represent mean difference with 95% confidence bounds.
Figure 1
Figure 1
Figure 1a. Contact ultrasound pachymeter versus Artemis-2 measurements of central corneal thickness. Figure 1b. Bland-Altman plot of the handheld US pachymeter compared with the Artemis-2. The horizontal lines represent mean difference with 95% confidence bounds.
Figure 2
Figure 2
Figure 2a. Orbscan II versus Artemis-2 measurements of central corneal thickness. Figure 2b. Bland-Altman plot of the Orbscan II compared with the Artemis-2. The horizontal lines represent mean difference with 95% confidence bounds.
Figure 2
Figure 2
Figure 2a. Orbscan II versus Artemis-2 measurements of central corneal thickness. Figure 2b. Bland-Altman plot of the Orbscan II compared with the Artemis-2. The horizontal lines represent mean difference with 95% confidence bounds.

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