Residence time refers to the duration at which the artificial tear resides on the eye. Methods have been developed to assess residence time by admixing fluorescent tracers to the solution and then measuring the amount of fluorescence over time. The caveat to methods using certain tracers has lead to uncertainty in elimination measurements due to corneal penetration or differing molecular weights (MW) from the active vehicle ingredient in the solution. For example, low-MW tracers can be eliminated at a different rate than higher-MW polymers. In addition, the low-MW tracers may be able to penetrate the corneal epithelium giving a false pre-corneal residence time. Meadows, Paugh, Joshi, and Mordaunt addressed this issue by developing a technique using a polymer which did not penetrate the cornea and had the same MW as the active ingredient in the solution FITC-dextran. Based on the assumption that similar weights are eliminated at the same rate, this technique has shown to be more economic, manageable, and amendable than previous procedures measuring residence time.