Kinetics of lacrimal secretion in normal human subjects

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Abstract
A novel technique was used to study the time course of lacrimation in normal human subjects with and without the use of topical anesthetic. The Schirmer technique was modified to eliminate evaporation, to improve absorption capacity, and to allow the determination of the length of paper strip wetted as a function of time. By the use of a theoretical model, the wetting curve thus obtained could be analyzed and basic secretion parameters characteristic of lacrimation kinetics were obtained. Fourteen adult females and six adult males between the ages of 21 and 47 years were included in the study. All the eyes examined exhibited essentially the same type of tear secretion kinetics. Initially, the lacrimation occurred at a high rate which then exponentially diminished to a final, lower value. This exponential cycle of secretion pattern could occur repeatedly during the time of measurement and was not qualitatively altered by the use of topical anesthesia. In addition to the time dependence of wetted length, we also determined the weight of the absorbed tears in the filter paper strips in order to obtain the average specific volume of wetting for each measurement. The specific volume of wetting is needed to convert wetting rates to secretion rates. Our results indicate that the novel method used may be developed into a sensitive but clinically applicable technique for determining lacrimation kinetics quantitatively in patients. The interrelationship between the kinetic parameters of tear secretion and the various types of lacrimal deficiencies remains to be determined.

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