Insights into Tear Film Stability from Babies and Young Adults: A Study of Human Meibum Lipid Conformation and Rheology

Abstract

Babies have the most stable tears and people with dry eye have the least stable tears. Meibum may contribute to tear film stability, so in this study, the hydrocarbon chain conformation and rheology of meibum from babies was studied for the first time. Infrared spectroscopy was used to measure lipid phase transitions. Rheology was measured using Langmuir film technology. Meibum from 25 donors 1 to 13 years old was compared with meibum from 18 donors 13 to 25 years old. The phase transition temperature and lipid order (stiffness) increased with increasing age from 1 to 25 years. The increase in meibum lipid order from 1 to 25 years of age may contribute to the instability of the tear film with age and contribute to films with a higher reciprocal compressibility modulus that are not as compressible and not as viscoelastic. Changes in the lipid phase transition parameters of meibum lipid with dry eye are an exacerbation of the changes observed with age. The lower reciprocal compressibility moduli of meibum films from children and babies compared with meibum from adults reiterates higher stability in their films which spread better, resist deformation, and facilitates their ability to be quickly restored after blinking.

Meibum lipid hydrocarbon chain branching and rheology after hematopoietic stem cell transplantation

“…Too much lipid order may keep meibum from flowing out of the meibomian glands. Relevant to the structure of lipids on the tear film surface, the findings of the current rheological experiments show that above 15 years of age the П max and at all ages, (C s −1 ) max increased with age for both PC and PT cohorts in accord with a previous study [ 27 ]. Higher П max and (C s −1 ) max values indicate the lipids become more elastic and stiffer with age.…”

“…One may speculate that more ordered lipid results in attenuated capability to restore tear film lipid layer structure between blinks. In M n lipid order increases with age between 0 and 25 years, while over 25 years lipid order slightly decreases which does not contribute to tear stability as over 25 years there is little change in tear stability [ 27 ].…”

Human Meibum Cholesteryl and Wax Ester Variability With Age, Sex, and Meibomian Gland Dysfunction

“…M n order increases with age between 0 and 20 years of age. The CE/WE ratio increased with age between 0 and 20 years of age; thus, in addition to saturation,44,54 CE could contribute to the increase in order, with age between 0 and 20 years,43 as a cholesteryl behenate increased the order of WE 28. Experiments are underway to determine the contribution of CE to the order of meibum by separating meibum CE from WE and adding the moieties back together, as was done for saturated meibum 44,54…”

“…Infrared9,42–54 and fluorescence anisotropy42 studies show that meibum lipid hydrocarbons align to maximize Van der Waal's interactions between chains. Therefore, the WE and CE hydrocarbon chains are not randomly orientated as they are in an oil phase, as many schematic pictures in literature show them to be.…”

Lipid Saturation and the Rheology of Human Tear Lipids

“…One measurement of lipid structure is termed ‘order,’ which is indirectly related to lipid fluidity that has an additional dynamic component. It is interesting that tear film stability and meibum lipid hydrocarbon order both increase in the order: Meibum from donors without dry eye between the ages of 0 and 25 years old [18,19] < meibum from donors with meibomian gland dysfunction [18,20,21] < meibum donors who are susceptible to severe dry eye who have had hematopoietic stem cell transplantation [18,22,23]. When dry eye signs and symptoms were ameliorated with treatment, lipid order was restored [21].…”