What is the normal TFBUT in healthy dogs versus dogs with EDED?

• A. 21s vs <5s
• B. 13.1s vs 3.7s
• C. 24.2s vs 14.9s
• D. 20s vs <5s

Answer: (A)

Tear film stability is what TFBUT measures: after blinking, how long until the first breakup or dry spot appears on the cornea when viewed with fluorescein. In healthy dogs, the tear film remains intact for a relatively long time, typically around twenty seconds, reflecting a stable lipid layer and adequate mucin and aqueous components. In dogs with evaporative dry eye disease, the tear film is unstable and evaporates quickly, so the break-up happens very soon—often in just a few seconds.

The pair that fits this pattern best is a normal around 21 seconds and an EDED value of less than 5 seconds. This reflects the clear contrast between normal tear film stability and the marked instability seen with evaporative dry eye. The other options either place the normal TBUT in an unusually short range or show only a modest drop for EDED, which wouldn’t align with the pronounced tear film instability characteristic of evaporative dry eye.