Abstract
Both lipids and mucins contribute to the stability of the tear film and lipids may inhibit tears from evaporating. Younger people have lower lipid viscosity, higher lipid volume, and a lower rate of tear evaporation. Since age-related changes in human meibum composition and conformation have never been investigated, as a basis for the study of lipid-associated changes with meibomian gland dysfunction, we used the power of infrared spectroscopy to characterize hydrocarbon chain conformation and packing in meibum from humans without dry eye symptoms in relation to age and sex. Meibum from normal human donors ranging in age from 3 to 88 years was studied. Meibum phase transitions were quantified by fitting them to a 4-parameter 2-state sigmoidal equation. Human meibum order and phase transition temperatures decrease with age and this trend may be attributed to lipid compositional changes. If meibum has the same thermodynamic properties on the surface of the tears as it does on the lid margin, a decrease in lipid-lipid interaction strength with increasing age could decrease the stability of tears since lipid-lipid interactions on the tear surface must be broken for the tear film to break up. This study also serves as a foundation to examine meibum conformational differences in meibum from people with meibomian gland dysfunction.