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We examined a group of normal subjects to evaluate the tear film function by measuring reflex tear capacity using the Schirmer test without anesthetic, steady state tear flow using fluorophotometry, meibomian gland function based on gland drop-out, expressible lipid volume and viscosity, tear loss from evaporation, and tear osmolarity. We found the average tear flow to be 0.19 +/- 0.19 microliters/min, lower than previously measured. The average tear volume was also correspondingly less, 2.74 +/- 2.0 microliters. We found there was a decline associated with advancing age for all parameters except the decay constant and lipid volume. The highest correlations with aging were tear volume (-0.64), Schirmer test (-0.63), and tear osmolarity (0.59). Our results indicate that there is a decline in tear film function throughout life and that tear flow is considerably less than previously estimated.
Mathers et al. (Wed,) studied this question.