To compare central corneal thickness (CCT) measurements by the Orbscan II device, contact ultrasound (US) pachymetry, and the noncontact Artemis 2 scanning US system.
Department of Ophthalmology, Weill Cornell Medical College, New York, New York, USA.
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.
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 μm ± 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 μm thinner than Artemis 2 values. Orbscan II values showed a trend toward increasing underestimation of CCT in thinner corneas.
Ultrasound pachymetry and Artemis 2 CCT measurements were highly correlated; the 11 μm 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 μm, Orbscan values were less correlated than Artemis 2 values with contact US pachymetry and were prone to underestimation of the CCT in thinner corneas.