prelens tear film

tear film, prelens 

Tear film found on the front surface of a contact lens on the eye. The oily layer of the film is slightly thinner with soft lenses than in the precorneal film and almost absent with rigid lenses. The aqueous layer is thinner with rigid lenses than in the precorneal film. The exact composition of the prelens tear film varies with the characteristics of the contact lens on the eye. See precorneal film.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann