Accuracy of Visante and Zeiss-Humphrey Optical Coherence Tomographers and their cross calibration with optical pachymetry and physical references

• Main Authors: Jyotsna Maram, Luigina Sorbara, Trefford Simpson
• Format: Article
• Language: English
• Published: Elsevier 2011-10-01
• Series: Journal of Optometry
• Subjects: Optical coherence tomography (OCT); Mechanical Gauge (MG); Optical Pachometer (OP)
• Online Access: http://www.sciencedirect.com/science/article/pii/S1888429611700577

Purpose: To calibrate the new ZEISS VisanteTM anterior segment optical coherence tomographer (OCT) using references with known physical thickness and refractive index equal to the human cornea and to compare the Visante measures to those from a previous generation OCT (Zeiss-Humphrey OCT II). Methods: Twenty two semi-rigid lenses of specified thicknesses were manufactured using a material with refractive index of 1.376. Central thickness of these lenses was measured using VisanteTM and Zeiss-Humphrey OCT II OCT's (Zeiss, Germany). Two data sets consisting of nominal measures (with a standard pachymeter) of the lenses and one obtained using a digital micrometer was used as references. Regression equations between the new physical and optical (OCT) measures were derived to calibrate the devices. Results: Before calibration, repeated measures ANOVA showed that there were significant differences between mean lens thicknesses from each of the measurement methods (p < 0.01), where Visante measurements were significantly different from the other three (OCT II, MG and OP) methods (p < 0.001). Visante thickness was significantly higher than the microgauge measures (453 ± 37.6 compared to 445.1 ± 38.2) and the OCT II was significantly lower (424.5 ± 36.1 both, p < 0.001). After calibration using the regressions between physical and optical measurements, there were no differences between OCT II and Visante (p < 0.05). Conclusions: Using references lenses with refractive index of the cornea (1.376) allows rapid and simple calibration and cross calibration of instruments for measuring the corneal thickness. The Visante and OCT II do not produce measurements that are equal to physical references with refractive index equal to the human cornea.