What is a reported effect of fluorescein dye on tear film stability during TFBUT testing?

• A. The dye increases tear production.
• B. The dye has no effect on tear film stability.
• C. The dye makes tear film more stable.
• D. Dye-Induced Instability: The addition of fluorescein dye can actually decrease tear film stability.

Answer: (D)

When tear film breakup time is measured, adding fluorescein can actually disturb the very film you’re trying to observe. The dye mixes with the tear film and can alter its surface properties, particularly at the air-tear interface, by affecting lipid layer behavior and mucin-spreading dynamics. This can make the tear film less stable and cause breakup to occur sooner, so the measured TBUT is artifactually shortened. In other words, fluorescein can induce instability in the tear film rather than increasing production or leaving it unchanged, which is why the observed effect is described as dye-induced instability.