The Reciprocal Relationship Between Blinking and Non-invasive Tear Break-up Time (NI-BUT): A Pilot Study Toward...

The non-invasive tear break-up time (NI-BUT) test is widely used to assess tear film stability in dry eye disease (DED); however, the test is performed under prolonged eye-opening conditions that do not reflect physiological blinking behaviour. Ignoring individual blink autoregulation may influence the interpretation of tear film instability. This study investigated the relationship between natural blink dynamics and NI-BUT parameters to explore a more individualised interpretation of tear film stability.

In this prospective observational pilot study, 50 young female participants (18-30 years of age) underwent NI-BUT testing and non-noticeable blink dynamic assessment. Blink frequency and interblink intervals (IBI) were extracted from 1-min video recordings, and a personalised average interblink interval (A-IBI) was calculated for each participant by averaging nine IBI values sampled at different time points. Associations between blink dynamics and NI-BUT parameters were analysed, and tear break-up times were evaluated relative to individual IBI ranges.

Interblink interval parameters exhibited statistically significant positive associations with NI-BUT measurements, with correlation strength increasing across successive tear break-up events (Spearman's r = 0.28-0.67; p < 0.05). Conversely, blink frequencies demonstrated statistically significant inverse associations with NI-BUT values (r = -0.29 to -0.42; p < 0.05). Although 74% of participants met the conventional NI-BUT-based criteria for tear film instability, most demonstrated sufficient blink autoregulation. Specifically, the first non-invasive tear break-up occurred after the personalised average interblink interval in 82% of participants and after the longest observed physiological interblink interval in 58%.

Associations between blink dynamics and NI-BUT parameters were observed in this pilot cohort. In many participants, the non-invasive first tear break-up event occurred after the individual's average IBI, suggesting that habitual blinking may contribute to the physiological context in which tear film stability measurements are interpreted. These findings should be considered hypothesis-generating and require validation in larger and clinically characterised populations.