Fluorescein Tear Break-Up Time (FTBUT)

Fluorescein tear break-up time measures the stability of the pre-corneal tear film after a blink. It is commonly used in the assessment of dry eye disease and other conditions in which tear-film stability is reduced.

How to do the test

  1. Instil a small amount of fluorescein into the lower conjunctival sac.
  2. Ask the patient to blink naturally a few times so that the dye is distributed evenly over the ocular surface.
  3. Select the Fluorescein / FTBUT mode in OSDx and focus the cornea.
  4. Ask the patient to blink once and then keep the eye open for as long as comfortably possible.
  5. Start the acquisition immediately after the blink. OSDx records the fluorescein pattern and assists in identifying the first significant area of tear-film break-up.
  6. Repeat if required when the recording is affected by blinking, poor focus or uneven fluorescein distribution.
Tip: Use the smallest practical amount of fluorescein. Excess dye can alter the tear film and may prolong the measured break-up time.

Understanding the result

The FTBUT is the interval between the last complete blink and the first visible disruption of the uniform fluorescein tear film. Shorter times indicate reduced tear-film stability.

A value below about 10 seconds is commonly considered abnormal, although interpretation should be made together with symptoms, staining, tear meniscus findings and other ocular-surface tests.

FTBUT is influenced by the amount of fluorescein used, blinking, room conditions and ocular-surface irregularity. Follow-up measurements are most useful when the examination technique is kept consistent.