To observe the emission intensity profile of sodium fluorescein
in the human tear film as a function of time and concentration.
Twenty-two participants with no dry eye signs or symptoms were randomly allocated to receive 1 μL of either a 2 or 10% concentration of fluorescein
to one eye. Images of the inferior tear meniscus
were captured at regular intervals over 30 minutes and the process repeated for the other eye with the alternate concentration. Fluorescence
intensity was quantified on the basis of the grayscale pixel values in the tear meniscus
images. The fluorescein
over time and between concentrations was determined.
intensity was reached in 3.9 ± 3.0 and 8.7 ± 4.4 minutes after instillation for the 2 and 10% concentrations, respectively. The 10% concentration of fluorescein
maintained its peak fluorescence
intensity longer than the 2% concentration (about 9 and 2 minutes, respectively). The peak fluorescence
intensity was not significantly different between the higher and lower concentrations (44 ± 37 vs. 38 ± 32 units, P
= .22). For both concentrations, the observed intensity did not return to baseline levels by the end of the 30-minute observation time.
intensity of fluorescein
in a clinical setting varies with time such that both the onset and duration of maximum brightness are concentration dependent. At low concentration (2%), maximum brightness occurs almost immediately after instillation and lasts about 2 minutes. With a higher concentration (10%), the effective working window is delayed for about 7 to 8 minutes. Irrespective of initial concentration, observable fluorescence
remains in the tear film beyond 30 minutes post-instillation.