Interface properties of simplified tear-like fluids in relation to lipid and aqueous layers composition.

Abstract

The Langmuir trough approach to the study of the physical properties of an in vitro system representing the natural tear lipid-aqueous interface gives useful information on the effect produced by changes of composition of both phases. We found that variations of the composition of the lipid mixture affect more strongly the characteristics of the film rather than changes in the aqueous phase composition. Therefore, future investigations should consider the possibility of searching for and optimising additions of lipid mixtures to the natural tear film. These novel mixtures should stabilise the lipid layer, and thus treat the evaporative Dry Eye Syndrome. More critical and worthy of further investigation is the effect of surface-active water-soluble components that can reduce and ultimately destroy the lipid film integrity and effectiveness. The beneficial effect of water-soluble components, either naturally occurring or artificially added, may be more precisely compared with possible side effects on the stability of the lipid tear layer. In any case, these side effects may be largely compensated by the presence of stability enhanced lipid composition. The present work may be considered as an introductory investigation that takes the physical-chemical approach into the realm of debated data about the tear film structure and properties. Refining the model we have adopted in the present work is certainly necessary. For instance, introducing into the model tear composition other components such as ceramides and cerebrosides will provide insight to their contribution to the packing structure. We may also couple different techniques such as measuring elastic and rheological properties of the films that may be relevant to its physiological behaviour.