To determine epithelial permeability, a micropipette is used to deliver 2 µl of 0.35% fluorescein onto the central superior bulbar conjunctiva of the subject's right or left eye, and the subject is instructed to close and roll his/her eye in order to evenly distribute the fluorescein to the tear film. The same eye is scanned within 45 seconds after dye instillation. Following this scan, the same procedure is repeated on the fellow eye and the two eyes are then alternately scanned approximately 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. Joshi A, Maurice D, Paugh J. A new method for determining corneal epithelial barrier to fluorescein in humans. Invest Ophthalmol Vis Sci 1996;37:1008-1016.