Tear Breakup Time

Synonyms

Breakup time (BUT); Fluorescein breakup time (FBUT); TBUT

Definition

The tear breakup time is a diagnostic procedure that examines the time that it takes for dry spots to appear on the corneal surface after blinking (Savini et al. 2008).

Purpose

The purpose of the TBUT is to evaluate the stability of the tear film and to detect the presence of evaporative dry eye. A TBUT greater than 10 s is considered normal. A value of less than 5 s indicates significant dry eye disease (Asbell and Lemp 2006).

Principle

The TBUT is performed as follows (Kastelan et al. 2013):

• Fluorescein dye (1–5 μl of 2% sodium fluorescein) is added to the lower fornix of the eye using a pipette or strip.

• The patient is asked to blink a few times in order to distribute the fluorescein and then is instructed to abstain from blinking.

• The tear film is then observed under a slit lamp using a broad beam with a cobalt blue filter.

• The presence of black spots will indicate dry spots on the tear film.

  ...