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Objectives: To evaluate the reproducibility of tear film kinetics (TFK) measurements during the full interblink period in habitual wearers of delefilcon A daily disposable contact lenses under different environmental
Methods: Two independent studies were performed, one involving 90 eyes measurements in 49 subjects and the second involving 58 eyes measurements in 32 subjects, after 3 hours of conventional wear in normal environmental conditions (NEC) and an additional 3 hours of computer use under adverse environmental conditions (AEC), defined as 20% relative humidity (RH). Digital videos were obtained by non-invasive Tearscope illumination, followed by a parallel-group post-hoc comparative analysis by masked investigators of the videos obtained during the two studies. Parameters analyzed included non-invasive break-up time (NIBUT); dehydration speed (DS) between the initial break and the spontaneous blink, and minimum protected area (MPA) of the lens surface by the tear film.
Results: After 3 hours of wear in normal environmental conditions, the overall population (n=148) had a mean NIBUT of 7.1 ± 7.0 sec, a mean DS of 0.28 ± 0.66 mm2/sec, and a mean MPA of 93.4 ± 16.6%. After an additional 3 hours in AEC, mean NIBUT was 8.4 ± 9.8 mm2/sec, mean DS was 0.26 ± 0.75 mm2/sec, and MPA was 95.2 ± 14.0%. The TFK characteristics in the two studies were similar for each environmental condition: after 3 hours of conventional wear, the mean [95% CI] differences between the two studies were −0.9 [−3.2, +1.4] sec for NIBUT, 0.00 [−0.22, +0.22] mm2/s for DS, and 2.0 [−3.5, +7.4] % for MPA; after an additional 3 hours of wear in 20% RH, the mean [95% CI] differences between the two studies were −1.3 [−4.5, +1.9] sec for NIBUT, −0.03 [−0.28, +0.22] mm2/s for DS and −0.3 [−4.9, +4.3] % for MPA. Conclusions: This analysis showed that the measurement of pre-contact lens TFK carried out in two differ-ent studies involving habitual wearers of delefilcon A having worn their contact lenses for an initial 3 hours under NEC and a further 3 hours under low (20%) hygrometry (AEC) produced similar on-eye wettability, including a long NIBUT, slow DS following the initial break, and wide MPA at the next blink. The results establish the reproducibility of the measurement of pre-contact lens TFK using the Tearscope; by quantifying the measurement variability, the data makes it possible to carry out precise sample size calculations in future studies involving pre-contact lens TFK measurements to quantify on-eye wettability under both normal and adverse environmental low (20% RH) hygrometric conditions.
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