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Analytical Performance, Spatial Dynamics and Clinically Meaningful Change Thresholds for Automated Non-invasive Tear
1Faculty of Health, University of Plymouth, Plymouth, UK. daniela.oehring@plymouth.ac.uk.
Purpose:
Non-invasive tear film metrics from automated topographers are used increasingly, yet device-specific analytical performance remains incompletely characterised. This study quantified the analytical performance of the Oculus Keratograph 5M for non-invasive break-up time (NIKBUT) and tear meniscus height (KTMH), evaluated agreement with conventional methods and characterised the spatial dynamics of tear film break-up.
Methods:
Thirty-five participants (18 symptomatic, 17 asymptomatic) attended three visits on consecutive days. NIKBUT (first and average), KTMH, fluorescein break-up time (FBUT) and slit-lamp tear meniscus height (TMH) were each measured three times per eye per visit. Precision (coefficient of variation, CV), reliability (intraclass correlation, ICC 3,1), standard error of measurement (SEM) and minimum detectable change at 95% confidence (MDC₉₅) were calculated. Method agreement was assessed using random-effects Bland-Altman analysis. Spatial distribution of break-up events was analysed by the corneal zone.
Results:
KTMH demonstrated excellent precision (CV = 8.8%) and moderate-to-good reliability (ICC = 0.73), with an MDC₉₅ of 0.173 mm. NIKBUT showed poor precision (CV = 53.6% for First, 42.8% for Average) and symptom-dependent reliability. FBUT required a change exceeding 9.28 s to surpass its MDC₉₅. Bland-Altman analysis confirmed systematic bias between NIKBUT and FBUT, with limits of agreement spanning more than 19 s in width and significant proportional bias. Spatial analysis revealed that NIKBUT break-up occurred predominantly paracentrally (53-63%), while FBUT events concentrated centrally (86-97%), indicating the methods captured fundamentally different tear film phenomena. Intra-subject repeatability of break-up location was poor (Krippendorff's α = 0.12-0.31).
Conclusions:
KTMH is the most analytically robust Keratograph metric, suitable for longitudinal monitoring when changes exceed its MDC₉₅ of 0.173 mm. NIKBUT shows poor precision; only large changes exceeded noise. Spatial analysis confirms that NIKBUT and FBUT interrogate distinct biophysical processes-these methods are not interchangeable. These benchmarks should inform clinical interpretation and study design.
