Poor mixing of microdrops with the tear fluid reduces the accuracy of tear flow estimates by fluorometry.

Abstract

The initial rapid fall in tear film fluorescence after instilling a 1 microliter drop of fluorophore could be a result of stimulated tear flow or of distribution of the dye throughout the tear fluid present in the conjunctival sac. An attempt was made to decide this by comparing the fall in fluorescence of two different fluorophores instilled at an interval of several minutes. In fact, very few patterns of initial rapid loss were found, but it was noted that there was usually a strong gradient of fluorescence from side to side across the cornea that took several minutes to dissipate. It seems that lateral mixing of a microdrop with the tear fluid is not instantaneous and that caution should be exercised in interpreting such measurements to estimate the total volume of tear fluid.