MEASUREMENT OF CORNEAL EPITHELIAL PERMEABILITY TO FLUORESCEIN - A REPEATABILITY STUDY

Purpose. Permeability (P-dc) to sodium fluorescein (F) is a characteri stic of the barrier function of the corneal epithelium. The repeatabil ity of several in vivo fluorophotometric methods used to measure perme ability in humans remains largely undocumented. This study examines th e repeatability of a method based on topical instillation of a single drop of F for the quantitative assessment of P-dc . Methods, Nine heal thy subjects with no history of ocular disease provided 1 (n = 1), 2 ( n = 1), or 3 (n = 7) repeated measurements of each eye at successive v isits. After making 3 baseline fluorescence scans centrally through th e tear film and cornea, 2 mu l of 0.35% 1; were instilled and 10 fluor escence scans were obtained at approximately 2-minute intervals immedi ately after instillation. Subsequently, the eyes were rinsed three tim es with nonpreserved saline and four additional scans were performed. Results. Pde was calculated by dividing the baseline-corrected postrin se stromal fluorescence by the time integral of the tear film fluoresc ence calculated over the 20-minute exposure period. After applying a l ogarithmic transformation to the P-dc, estimates, a mixed-model analys is was used to assess measurement repeatability. On the P-dc stale, th ere is an estimated 95% chance that a second measurement could be as m uch as 2.88 times higher or 0.35 times lower than a first measurement. Conclusions. This substantial variability between repeated measuremen ts indicates that the single-drop procedure is unreliable for monitori ng individual patient changes. However, with careful sample size plann ing, this technique can be used in population-based research to compar e differences in treatment effects between groups of subjects.