Analytical performance, spatial dynamics, and clinically meaningful change thresholds for automated non-invasive tear film assessment using the Oculus Keratograph 5M

Purpose Non-invasive tear film metrics from automated topographers are increasingly used, 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 (NIKTMH), 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), NIKTMH, fluorescein break-up time (FBUT), and slit-lamp tear meniscus height (TMH) were each measured three times per eye per visit. Precision (CV), reliability (ICC 3,1), standard error of measurement (SEM), and minimum detectable change (MDC₉₅) were calculated. Method agreement was assessed using random-effects Bland-Altman analysis. Spatial distribution of break-up events was analysed by corneal zone. Results NIKTMH demonstrated excellent precision (CV = 8.8%) and moderate-to-good reliability (ICC = 0.727), 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 exceeding ± 19 s and proportional bias. Spatial analysis revealed that NIKBUT break-up occurred predominantly paracentrally (53–63%), while FBUT events concentrated centrally (86–97%), indicating the methods capture fundamentally different tear film phenomena. Intra-subject repeatability of break-up location was poor (Krippendorff’s α = 0.115–0.308). Conclusions NIKTMH 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 exceed 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.