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Five-year trend of tear break-up time (BUT) at three clinics (A–C). BUT continuously decreased from 2015 to 1919, and this trend was stable across the three participating clinics. Mean BUT in 2018 and 2019 (black symbol, black line) was shorter than in 2015 (*p < 0.001, vs 2015, Mann–Whitney U test with Bonferroni correction).
