Comparison of horizontal corneal diameter measurements using Orbscan IIz, OPD Scan III, and IOLMaster 700

Purpose: To compare 3 automated devices for measuring the horizontal corneal diameter [white-to-white (WTW) distance]. Methods: In 65 eyes of 38 patients, the WTW distance was measured independently using Orbscan IIz tomography system (Bausch & Lomb), IOLMaster 700 (Carl Zeiss Meditec) and OPD Scan III (NIDEK). We tested for systematic differences in measurements and estimated the limits of agreement (LoA) using linear mixed effects models. Results The mean WTW distance was 11.8 0.40 mm with Orbscan IIz, 12.1 0.5 mm with IOLMaster 700 and 12.0 0.4 mm with OPD Scan III. The mean difference between IOLMaster 700 and Orbscan IIz was 0.33 (95% CI 0.28;0.38) (p<0.001), between OPD Scan III and Orbscan IIz was 0.24 mm (95% CI 0.21;0.28) (p<0.001), and between IOL Master 700 and OPD Scan III was 0.09 (95% CI 0.05;0.12) (p<0.001). The 95% LoA for Orbscan IIz versus IOLMaster 700 was -0.69 mm to 0.03 mm, Orbscan IIz versus OPD Scan III was -0.52 mm to -0.03 mm, and OPD versus IOLMaster 700 was -0.39 mm to 0.22 mm. Switching to IOLMaster 700 or OPD Scan III measurements led to a selection of a longer phakic IOL length (Visian ICL, STAAR) in 34% and 33% of the cases, respectively compared to Orbscan IIz. Conclusions: The data suggests that these devices are not interchangeable for usual clinical practice. Adjustments based on mean differences was not enough to compensate for inter-instrument discrepancy in WTW measurements.