Function of meibomian glands and tear pH

Each of ten persons had ten meibomian orifices studied by triple‐vital‐staining. Activity was disclosed in 43%, these being stained by lipid‐specific Sudan III power. 5% were stained by lissamine green (obstructed by a plug of degenerate cells), 1% also by fluorescein (damaged epithelium). After one week 6% of the meibomian glands became inactive, while 5% gained activity, showing a cyclic function. In 38 subjects expression of meibomian secretion effected a significant fall of the tear pH value, from 6.91 ± 0.24 to 6.64 ± 0.26 (mean ± SD). The meibomian secretion alters the tear pH towards higher acidity. The importance of this fact is discussed.