Air pollutants and tear film stability--a method for experimental evaluation.

Instability of the pre-ocular tear film causes symptoms of dry eyes. Tear film instability may be caused by exposure to air pollutants, but identification of causative agents is often difficult. We describe an in vitro technique for assessment of putative agents on the surface activity of Meibomian lipids. The lipids were obtained from bovine eyelids and dissolved in chloroform. Surface activity of the solution was assessed on a Wilhelmy balance. After addition of benzalkonium chloride, minimum surface tension of the lipids increased and maximum surface tension fell. After addition of quartz particles, both maximum and minimum surface tension increased. The method can be used to screen substances suspected to cause dry eyes, providing a basis for selection of substances for in vivo studies.