Repeatability and reproducibility of macular thickness measurements with the Humphrey OCT system

To assess the accuracy, precision, repeatability, and reproducibility of measurements made by the Humphrey optical coherence tomography (OCT) system (Humphrey-Zeiss Medical Systems, San Leandro, CA).

The performance of the system was first investigated by scanning a test object containing an air gap of known size. Measurements were repeated with water or glycerin in the gap. In the clinical setting, macular thickness measurements were obtained from a control group of 20 normal subjects. For analysis, these scans were divided into eight sections, each containing 10 A-scans.

The average gap thickness was found to be close to the true value in all cases. The overall coefficients of intersession reproducibility were less than 1% for the test object and 1.51% for the control group. There was no significant difference between scans acquired during different sessions. The overall coefficients of repeatability for the test object were between 0.2% and 1.1% and between 1% and 2% for the control group. The range of normal retinal thickness in terms of the 5th and 95th percentiles was 222 to 248 microm in women and 234 to 257 microm in men.

Measurements made from OCT scans were found to be accurate and precise. Introducing water or glycerin into the test object resulted in considerable degradation of the signal, but measurements of gap thickness were still shown to be accurate, precise, reproducible, and repeatable. Retinal thickness measurements in the macular area were repeatable and reproducible. This demonstrates that OCT is a useful tool in the monitoring of patients with conditions that affect macular thickness, even when there is considerable degradation of the OCT signal.