To determine epithelial permeability, a single fluorescein drop is used. The eye is scanned within 45 seconds after, then every two minutes for the next 20 minutes (typically for a total of 10 scans per eye). To determine the amount of dye that penetrated the epithelium, both eyes are thoroughly rinsed 3 times with nonpreserved, sterile saline, and stromal fluorescence levels are measured 5 times over the next 10 minutes. Researchers are very interested in this since bacterial infection usually requires a disruption of the epithelium. Changes in permeability in diseases such as diabetes may help explain related corneal complications.