A novel method to evaluate residence time in humans using a nonpenetrating fluorescent tracer

Invest Ophthalmol Vis Sci. 2002 Apr;43(4):1032-9.


Purpose: The purpose of these investigations was to develop an improved method for measuring precorneal residence time (RT) and to demonstrate its efficacy with novel formulations.

Methods: A biomicroscope was adapted for use as a clinical fluorometer. Using a nonpenetrating fluorescent probe (FITC-dextran, 70,000-73,000 molecular weight [MW]), RT was estimated as the time to return to baseline (gross RT) and from parameters derived from least-squares regression fits to the decay data (area under the curve [AUC], elimination rate, and time for 50% of the signal to be eliminated [T(50)]). One rabbit and two human studies were conducted. The studies were randomized, double-masked, and controlled. Repeatability in humans was examined in 15 subjects (six determinations per subject, n = 90 total).

Results: The FITC-dextran tracer did not penetrate into corneal tissue. The rabbit gross RTs were 14.5, 15.0, and 16.0 minutes for three low-viscosity solutions (eta = 2.7-7.7 mPa/sec) and 22.5 minutes for a more viscous solution (eta = 357 mPa/sec). For a high-viscosity (eta approximately equal 30,000 mPa/sec) gel in humans, the method demonstrated approximately a twofold increase in gross RT and AUC compared with buffered saline. Repeatability of the method appeared acceptable, with intersubject variability the most significant factor affecting precision.

Conclusions: The new method is safe and convenient and offers comprehensive RT data. Furthermore, it appears to differentiate among formulations. However, as with other tear-influenced parameters, there is significant variability. Thus, sufficient sample sizes are necessary for meaningful comparative investigations.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Animals
  • Area Under Curve
  • Cornea / metabolism*
  • Dextrans / pharmacokinetics*
  • Diagnostic Techniques, Ophthalmological*
  • Double-Blind Method
  • Female
  • Fluorescein-5-isothiocyanate / analogs & derivatives
  • Fluorescein-5-isothiocyanate / pharmacokinetics*
  • Fluorescent Dyes / pharmacokinetics*
  • Fluorophotometry
  • Gels
  • Half-Life
  • Humans
  • Male
  • Middle Aged
  • Rabbits
  • Reproducibility of Results
  • Viscosity


  • Dextrans
  • Fluorescent Dyes
  • Gels
  • fluorescein isothiocyanate dextran
  • Fluorescein-5-isothiocyanate