POOR MIXING OF MICRODROPS WITH THE TEAR FLUID REDUCES THE ACCURACY OFTEAR FLOW ESTIMATES BY FLUOROMETRY

The initial rapid fall in tear film fluorescence after instilling a 1 mu l drop of fluorophore could be a result of stimulated tear flow or of distribution of the dye throughout the tear fluid present in the co njunctival sac. An attempt was made to decide this by comparing the fa ll in fluorescence of two different fluorophores instilled at an inter val of several minutes. In fact, very few patterns of initial rapid lo ss were found, but it was noted that there was usually a strong gradie nt of fluorescence from side to side across the cornea that took sever al minutes to dissipate. It seems that lateral mixing of a microdrop w ith the tear fluid is not instantaneous and that caution should be exe rcised in interpreting such measurements to estimate the total volume of tear fluid.