Effect of blinking on the measurement of tear evaporation rate

PURPOSE: To evaluate the reliability and agreement of tear film evaporation measurements under different blinking conditions. METHODS: Ninety-six healthy volunteers (96 eyes) were recruited. Tear evaporation was measured using the Eye Vapometer under four randomized conditions: no-blinking, natural blinking, controlled blinking (one blink every 3 s), and eyes-closed. Raw evaporation rates were recorded in three consecutive measurements for each condition. Tear evaporation rates (TER) were calculated by subtracting the raw evaporation rate with eyes-closed from the other three conditions. Reliability of raw measurements were assessed, and agreement between TER values was evaluated using the Bland-Altman method. RESULTS: Consecutive measurements taken under the no-blinking condition showed significant differences (p ≤ 0.04). The repeatability values for no-blinking, natural blinking, controlled blinking and eyes-closed were 56.12, 44.78, 42.46 and 22.32, respectively. The no-blinking condition provided significantly higher TER values than natural blinking (p < 0.001) and controlled blinking (p = 0.005). CONCLUSIONS: Blinking affects the reliability of evaporation measurement, with the least reliable condition being no-blinking. TER under the natural blinking condition shows good reliability and best represents physiological function during daily activities; therefore, it appears to be the most appropriate condition for TER evaluation.