Fluorescein Dye Disappearance Test (FDDT / TCA)

The fluorescein dye disappearance test evaluates the clearance of fluorescein from the tear meniscus over time. OSDx can record the change in fluorescein signal and derive a tear clearance analysis (TCA) curve.

Clinical relevance

Delayed clearance may occur in lacrimal drainage obstruction, reduced lacrimal pump function, marked ocular-surface inflammation or situations where tear turnover is reduced. The test can be particularly useful when lacrimal pump failure is suspected despite an apparently patent drainage system.

How to do the test

  1. Instil a standard small amount of fluorescein into the lower conjunctival sac.
  2. Ask the patient to blink naturally and then look straight ahead.
  3. Select the FDDT / TCA mode in OSDx.
  4. Focus the lower tear meniscus, particularly the medial portion where the fluorescein signal is being analysed.
  5. Start the study and allow the patient to blink normally. Avoid touching the lids or ocular surface during the recording.
  6. OSDx tracks the fall in fluorescein intensity over time and generates the clearance curve and derived parameters.
For comparable follow-up studies, use a similar fluorescein volume and avoid additional drops during the measurement period.

Understanding the result

Normal tear clearance produces a progressive reduction in fluorescein intensity. Delayed disappearance produces a flatter or more slowly declining curve.

The derived half-time and clearance trend should be interpreted with the clinical examination. Abnormal clearance alone does not identify the exact site or cause of lacrimal dysfunction.

FDDT/TCA complements, but does not replace, lacrimal syringing, probing or imaging when structural nasolacrimal obstruction is suspected.