There are two methods for measuring corneal epithelial permeability which can be used with the Fluorotron.
One method is the immerse the cornea in an eyebath of fluorescein for a fixed amount of time. Then, the eye is thoroughly rinsed to remove all dye from the tears. The remaining fluorescein that has penetrated the corneal epithelium can be measured by the Fluorotron.
The second method, preferred by many for clinical studies, is to use a single drop of fluorescein instead of the eyebath. In this case, the total fluorescein must be measured while the fluorescein is still in the tear film, then again after the eye is rinsed. The Fluorotron program can also compute epithelial permeability from this data.
Selected References:
deKruij J, Boot J, Laterveer L, van Best J, Ramselaar J, Oosterhuis J. Simple method for determination of corneal epithelial permeability in humans. Curr Eye Res 6:1327-1334 (1987). PubMed
Joshi A, Maurice DM, Paugh JR. A new method for determining corneal epithelial barrier to fluorescein in humans. Invest Ophthalmol Vis Sci 37:1008-1016 (1996). PubMed
Leong YY, Tong L. Barrier function in the ocular surface: from conventional paradigms to new opportunities. Ocul Surf 13(2):103-9 (2015). PubMed
A more complete bibliography can be found here.