Confounding factors in the tear break-up time test. Influence of sequential measurements

The tear break-up time (BUT) test is important in diagnosing and monitoring tear film stability, and understanding potential changes in tear film dynamics during repeated measurements could improve the accuracy and reliability of the test in clinical practice. The study aimed to examine the changes in BUT value caused by subsequent measurements made in BUT test. A total of 120 female participants were divided into groups (30 individuals each). Participants were divided into four groups based on the interval between two non-invasive tear break-up time (NI-BUT) tests: Group 1 (1-minute interval), Group 5 (5-minute interval), Group 10 (10-minute interval), and Group 15 (15-minute interval). The first NI-BUT test was called Initial NI-BUT (NI-BUT(I)), and the second test was called Subsequent NI-BUT (NI-BUT(S)). The first BUTvalue (BUT1st), the second BUT value (BUT2nd), the third BUT value (BUT3rd), the fourth BUT value (BUT4th), the fifth BUT value (BUT5th), and the average value of the first three BUTs (BUTA3) were compared between the NI-BUT(1) and NI-BUT(S) tests. Participant ages ranged from 18 to 36 years, with a mean of 25.1 ± 3.2 years. The mean values of BUT1st, BUT2nd, BUT3rd, BUT4th, BUT5th, and BUTA3 in the NI-BUT(I) test were statistically significantly shorter than those in the NI-BUT(S) test for all groups (p < 0.05). The changes in the parameters were statistically significantly greater in Group 1 compared to the other groups (p < 0.05). Subsequent measurements cause increased BUT values. The longer the interval between two measurements, the smaller the differences between the subsequent measurements. When performing the BUT test, a single measurement should be preferred if possible. If the clinician finds the results of a single measurement unsatisfactory and wishes to consider the average of multiple measurements, the interval between tests should be longer than 15 minutes.