METHODOLOGICAL ASPECTS OF TEAR FLOW DETERMINATION BY MEANS OF A RADIOACTIVE TRACER

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Abstract
Theoretical considerations on a simplified biological system representing the tear pathways led to the assumption of an exponential pattern of elimination of tracer substances from the conjunctival sac [human]. The tracer used in the present study was technetium, Tc99m, as sodium pertechnetate. The detection system consisted of a .gamma. camera coupled to a digital system, a minicomputer and a magnetic tape unit. After instillation of 10 .mu.l normal saline solution containing Tc99m, the decay of activity was followed by an activity-time function curve to which exponential curves were approximately by the computer. As a parameter for tear flow the fractional turnover rate was calculated from 7-15 min after instillation. An initial faster elimination was found in the first 7 min following instillation. Corrections for background radiation, evaporation of water and transconjunctival transport of Tc99m were estimated.