The meibomian gland oils were found to be insoluble in water and could not be hydrated. These oils, when warmed to body temperature, could spread to form a thick multimolecular film which could not retard evaporation.
Brown SI, Dervichian DG. The Oils of the Meibomian GlandsPhysical and Surface Characteristics. Arch Ophthalmol. 1969;82(4):537-540. doi:10.1001/archopht.1969.00990020539019