Collection method dependant concentrations of some metabolites in human tear fluid, with special reference to glucose in hyperglycaemic conditions

Concentrations of the metabolites glucose, lactate, pyruvate, and urea were determined in human tear fluid. Collection of the tears in glass capillaries, without mechanical irritation, permitted the estimation of naturally occurring levels of these metabolites. Glucose concentrations were very low, also in diabetics with high blood glucose levels. Lactate was present at higher levels and pyruvate and urea in about the same concentrations as normally for blood. Collection of the tears with filter paper strips as absorbent material caused slight epithelial damage and consequently a loss of the barrier function of the epithelium. In filter paper eluates glucose concentrations were found to be much higher, especially in diabetics with high blood glucose levels. Lactate and pyruvate concentrations were not influenced, whereas the urea concentrations decreased. The value of clinical tear glucose tests is discussed.