We studied the behaviour of three lipid tear products, commercialised by the 
same brand, as Langmuir films at the air/liquid interface to simulate the ocular 
environment. No significant differences were observed in the surface behaviour 
of two of them disclosing the same composition, but commercialised for different 
applications. The interaction of several subphases, namely sodium chloride, 
glucose, albumin and lysozyme present in the natural tear, with the lipid films 
was assessed at room temperature and the temperature of human tear using surface 
pressure-area isotherms and elastic modulus plots. There is a notable influence 
of sodium chloride and the proteins albumin and lysozyme on the surface 
pressure-area isotherm of the lipid Langmuir films. Albumin shifted this 
isotherm to lower areas while an opposite shift was caused by lysozyme. These 
studies could be useful for the formulation of new lipid-containing artificial 
tears, and for increasing the confidence of the customers in commercial eye care 
formulations.