Agreement between invasive and noninvasive measurement of tear film breakup time

The agreement between fluorescein breakup time (FBUT) estimates and noninvasive breakup time (NIBUT) estimates automatically acquired using two videokeratoscopes was assessed. Small-cone (E300, Medmont) and large-bowl (K5M, OCULUS) Placido-ring–based videokeratoscopes were utilized for automated NIBUT estimation and fluorescein strip method was used for FBUT estimation. 33 subjects completed the study. Clear instructions were given regarding the blink before measurements. Bland–Altman analysis was used to test the agreement between tear film breakup time estimates and repeated measure analysis of variance was used to test the differences between measurement types. In comparison to FBUT, E300 NIBUT estimate was shorter (− 0.6 ± 2.6 s), whereas K5M NIBUT estimate was longer (3.3 ± 2.4 s). Limits of agreement for FBUT vs. E300 was 29.8 s, for FBUT vs. K5M 26.4 s, and 31.4 s for E300 vs. K5M. There were significant differences between tear film breakup times (F = 3.59, df = 2, P = 0.032). E300 and K5M NIBUT measurements have poor agreement with FBUT, even when blinking is precisely clarified. Agreement was better for shorted break up times than that for longer ones but in general NIBUT measurements are not interchangeable.