*2.5.6 Noninvasive keratograph breakup time (NIKBUT)*

The tear breakup time (TBUT) was considered one of the most repeatable tear film measurements and although invasive, easy to perform, and interpret [63, 64]. TBUT traditional objective tests are often limited by their invasiveness and low test repeatability and reproducibility [64]. For this reason, new methods of evaluation of the tear film emerged and with the help of the keratograph 5M (K5M) topography, a more objective way of evaluating tear film stability emerged; calling this measurement noninvasive keratograph breakup time (NIKBUT). The time is measured in seconds between the last complete blink and the first alteration of the Placido rings projected on the corneal surface, which the device automatically detects and


*Tomado de [59].*

## **Table 2.**

*Evaluation of tear rupture time.*

**Figure 5.** *NIKBUT.*

measures. K5M performs two measurements for NIKBUT: the time when the first tear film break occurs (NIKBUT-first) and the average time of all tear incidents (average NIKBUT) (**Figure 5**). Oculus K5M provides noninvasive, objective, and reproducible tear film measurements [65].
