The precorneal tear film is a very thin fluid layer over the corneal surface. Although it is a part of the tear fluid, it deserves to be considered separately because of its morphologic peculiarities and also because of its physiologic importance for the underlying cornea.
There have been numerous studies of the chemical composition and flow of tear fluid,1 but studies of the precorneal tear film have been limited. Wolff2,3 described the precorneal tear film as a layered structure and discussed some of its physiologic aspects. His conclusions on the physiology, however, seemed to be based on slit lamp observations.
The importance of the tear film for the underlying cornea has been pointed out by several authors. Smelser4 showed that the uptake of atmospheric oxygen through the tear film is necessary for normal corneal metabolism which, in turn, is essential for maintenance of the normal deturgescent state