Blink Time, Type Key to Quality Tear-Film Assessment

CLOSE UP: Pretty green eye frantically looking around bright room. Woman wearing mascara opens eye to continue reading. Iris moving from side to side and pupil contracting and expanding.
Study authors analyzed the importance of the type of blink and how it affected the tear-film breakup time.

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. 

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