Hydrogen ion concentration of tear fluid in newborn infants.

Tear pH was measured in 173 newborn infants by immersing the tip of a microcombination glass pH probe in the tear fluid lateral in the closed lower conjunctival sac. The median tear pH value was 6.8 with 95% interpercentile range 6.2 to 7.2. The mean tear pH value was 6.74 +/- 0.26 (SD). The pH value was not related to age within the first 12 days and not influenced by the mode of delivery or local application of 0.67% argenti nitratis. This method is an easy, reliable examination to record the pH values of tear fluid, and may widen the knowledge of tear function in normal and pathological conditions.