Repeatability and reproducibility of axial length, anterior chamber depth and crystalline lens thickness measurements using the Nidek US-500 Echoscan

Abstract

Aim: The reliability of an instrument used to collect data for clinical and research purposes is greatly important, especially when it is used to determine changes in measured ocular parameters over time. The purpose of this study was to determine the intra-session repeatability and inter-session reproducibility of axial length (AL), anterior chamber depth (ACD) and crystalline lens thickness (LT) measurements using the Nidek US-500 Echoscan.

Method: Fifty successive automatic measurements of the above parameters were taken on the right eyes only of 12 healthy subjects aged 23–44 years old, followed by similar repeated measures after 1 week. Sample standard deviations (s.d.), precision (P) and coefficient of repeatability (COR) were calculated to determine intra-session repeatability. Coefficient of reproducibility (CRP), Bland and Altman plots, concordance correlation coefficients (CCC) and paired t-tests that compared measurements obtained in the first and second sessions, were used to determine inter-session reproducibility.

Results: Both the intra-session repeatability and inter-session reproducibility were within acceptable limits for the three variables assessed.

Conclusion: The study showed that the Nidek US-500 Echoscan provides accurate, repeatable and reproducible measurements of AL, ACD and LT in healthy eyes. This finding will be of interest to optometrists and ophthalmologists who measure these parameters when diagnosing, managing and investigating conditions such as primary angle-closure glaucoma and keratoconus.