TränenfilmBreakupTime

Tränenfilm Breakup Time, commonly abbreviated TBUT, refers to the interval between a complete blink and the first appearance of a disruption in the tear film on the ocular surface. It is a measure of tear film stability and is used in the evaluation of dry eye disease and ocular surface health. The term is frequently translated as tear film breakup time (TBUT) in English-language literature.

TBUT can be measured by two primary methods: fluorescein tear breakup time (FTBUT) and non-invasive tear breakup time (NITBUT). In FTBUT, fluorescein dye is instilled into the tear film. After a blink, the patient keeps eyes open, and with a slit lamp and cobalt blue light the clinician records the time to the first fluorescein-stained break. In NITBUT, tear film stability is assessed without dye, using infrared imaging, interferometry, or other non-contact devices.

Normal TBUT values depend on age and population, but a common reference is greater than about 10 seconds for healthy individuals. Shorter TBUT indicates tear film instability and is commonly associated with dry eye, particularly evaporative dry eye linked to meibomian gland dysfunction, or aqueous-deficient dry eye when combined with other signs.

TBUT results can be influenced by technique, lighting, dye concentration (for FTBUT), environmental conditions, and blinking patterns. Fluorescein can itself alter tear dynamics, potentially shortening TBUT, while non-invasive methods may yield different normative values. Therefore TBUT should be interpreted alongside symptoms and other ocular surface tests.

TBUT is a core element of dry eye assessment and is incorporated in diagnostic criteria such as DEWS II, but is not a standalone test. It provides a measure of tear film stability rather than a direct measure of tear quantity.