Background: The aim of this study was to compare basal tear turnover values of healthy volunteers in different countries.
Methods: Healthy volunteers aged between 20 and 70 years were selected in three European cities. Basal tear turnover values were calculated according to a standardized protocol from the decay of the fluorescein concentration in tears after instillation of 1-microliters drop of fluorescein in the conjunctival sac. Fluorescein concentration was measured with identical commercial fluorophotometers. A mono-exponential decay of fluorescein was assumed to represent basal tear flow.
Results: The mean tear turnover values were 13.1%/min +/- 4.6 SD (n = 4), 16.0%/min +/- 5.2 SD (n = 24) and 17.5%/min +/- 3.4 SD (n = 20) in Clermont-Ferrand (France), Leiden (The Netherlands) and Madrid (Spain), respectively. The differences between the values were not significant (Mann-Whitney test P > 0.09).
Conclusions: The tear turnover in the different cities was similar. The methods used were simple and the software easy to use.