How does noninvasive tear film breakup time (NIBUT) work?

• A. Light is shone onto the ocular surface with a grid insert and the time it takes for projected lines to distort is determined.
• B. It uses fluorescein to visualize tear film.
• C. It measures tear production.
• D. It involves contact lens wear.

Answer: (A)

Noninvasive tear film breakup time works by projecting a grid or pattern onto the tear film and timing how long it takes for that pattern to distort after a blink. A healthy, stable tear film reflects the grid cleanly; as the tear film starts to break up, the reflection becomes distorted or breaks up in places. The time from a full blink to the first distortion marks the breakup time. This method is noninvasive because no dye is instilled and no contact with the eye is needed.

Other approaches involve dyes, like fluorescein, to visualize the tear film and assess breakup, which is a different, dye-based method. Measuring tear production (how much tear fluid is produced) is a separate test, not a measure of tear film stability. And involving contact lens wear isn’t required for this measurement and doesn’t define the technique.