Blink time was determined to “substantially impact” tear-film surface quality assessment when evaluating tear-film break-up time. Therefore, it is key to give patients clear and precise instructions on how to blink for the most accurate results with the test, study authors report.

Investigators used 2 types of videokeratoscopes, a fluorescein test, and a subjective experienced observer marking noticeable distortion in the Placido-disk pattern to learn how much the type of blink impacts tear-film breakup time, according to the study, published in Optometry and Vision Science

The 33 volunteers (11 male and 22 female) were assessed for 2 types of blinks: a short, natural blink and an unnaturally prolonged, forced blink. 

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Using statistical analyses with 2-way ANOVA and paired-sample t test, they found that the forced blink significantly shortened tear-film breakup time in all ways they measured (2-way ANOVA, P =.003). Mean difference between the breakup time after the natural and the forced blink was 3.2 (P =.002), 2.4 (P =.005), and 2.1 seconds (P =.002), for the videokeratoscopes, and fluorescein test, respectively. Between objective and subjective noninvasive breakup time, the group median of difference was less than 1 second with both videokeratoscopes.

One notable limitation was a lack of monitoring for the duration of blinks, which could be a consideration to inform future studies.

“When a patient’s blink is unnaturally prolonged, noninvasive tear-film breakup time is statistically and clinically significantly shorter than that observed for close-to-natural blinking conditions. This phenomenon can lead to wrong judgments of tear-film stability. Likewise, forced blinks seem to induce more abrupt tear-film destabilization than close-to-natural blinks. Therefore, it is of paramount importance to give precise instructions about the blink to a subject when conducting tear-film stability measurements,” the investigators wrote.


Szczesna-Iskander DH, Clara Llorens Quintana CL. Subjective and objective evaluation of the effect of blink type on tear-film breakup time and its estimation. Optom Vis Sci. 2020;97(11):954-961. doi: 10.1097/OPX.0000000000001592