Orbscan may overestimate corneal thickness measurements

This study compared the results of central corneal thickness (CCT) measurements taken with four different techniques: slit-lamp-mounted optical coherence tomography (SL-OCT, Heidelberg Engineering), conventional ultrasound pachymetry (Heidelberg Engineering), optical low coherence reflectometry (OLCR, Haag-Streit) and scanning-slit pachymetry (Orbscan, Bausch & Lomb).

The authors retrospectively analyzed pachymetric data of 20 patients (40 eyes) examined at one hospital with all four CCT measurement techniques. They found that the mean measurements taken with ultrasound, OLCR and SL-OCT were similar. However, there were significant differences between the mean measurements made with OLCR and the Orbscan (P = 0.0247), and the Orbscan detected slightly thicker values than the other methods.

The authors conclude that while CCT measurements taken using conventional ultrasound and the nontouch technologies of SL-OCT and OLCR were comparable, extreme care must be used in interpreting results obtained with Orbscan, as this technique may overestimate CCT significantly.