  Fluorescein is perhaps the most commonly used substance to visualize tear
film thickness and dynamics; better understanding of this process aids
understanding of dry eye syndrome which afflicts millions of people. We study a
mathematical model for tear film flow, evaporation, solutal transport and
fluorescence over the exposed ocular surface during the interblink. Transport
of the fluorescein ion by fluid flow in the tear film affects the intensity of
fluorescence via changes in concentration and tear film thickness. Evaporation
causes increased osmolarity and potential irritation over the ocular surface;
it also alters fluorescein concentration and thus fluorescence. Using thinning
rates from in vivo measurements together with thin film equations for flow and
transport of multiple solutes, we compute dynamic results for tear film
quantities of interest. We compare our computed intensity distributions with in
vivo observations. A number of experimental features are recovered by the
model.
