Purpose: Meibum lipids are believed to be important to tear film stability, but tear film lipid compositional, structural and functional relationships are not well established. The hypothesis that meibum lipid composition and structure change with age and meibomian gland dysfunction (MGD) was tested.
Methods: 1H-NMR was used to quantify meibum lipid composition. Fourier transform infrared spectroscopy was used to measure lipid structure, and Langmuir trough technology was used to measure tear film lipid rheology. Meibum was collected from 46 donors without dry eye and 48 donors with MGD.
Results: The molar ratio of Cholesterylesters/Wax ester increased with age, P = 0.007, from 0.43 Â± 0.02, n=39, to 0.52 Â± 0.02, n=17 in cohorts aged 1 to 12 and 13 to 19 years old, respectively. The same molar ratio decreased, P =0.011, from 0.50 Â± 0.03, n=38, to 0.34 Â± 0.04, n=48, for cohorts aged 20 to 88 years old with and without MGD, respectively. The molar ratio of =C-CH2 /ester increased with age, P = 0.007 from 1.73 Â± 0.17, n=36, to 2.55 Â± 0.24, n=19, for cohorts aged 1 to 12 and 13 to 19 years old, respectively. The same molar ratio decreased, P< 0.0001, from 2.06 Â± 0.25, n=34, to 0.19 Â± 0.03, n=37, for cohorts aged 20 to 88 years old, with and without MGD, respectively. Compared with meibum from donors without dry eye, meibum from donors with MGD contained less straight-chains, 50 Â± 2 % verses 57 Â± 1 %,P = 0.0003, moreiso-branched chains, 32 Â± 2 % verses23 Â± 1 %, P< 0.0001 and the same amount, 18.0 Â± 0.7 % verses 20 Â± 1 %, P = 0.34, of anteiso-branched hydrocarbon chains.
Conclusions: The changes in meibum composition with age and MGD contribute to the increase in lipid order of the same samples from donors without compared with those with MGD. Higher lipid order is associated with a higher reciprocal compressibility modulus that results in a tear film lipid layer that is not as compressible and not as viscoelastic. Strong lipid-lipid interactions could contribute to the aggregation of tear film lipids and contribute to a decrease in tear film spreading and dry eye.
Dr. Borchman received B.S. and Ph.D. degrees from Wayne State Unviersity before completing postdoctoral training at Mount Sinai Hospital in New York. His research is focused on ophthatmology and visual sciences, where his team recently characterized changes in human lens lipid composition with regard to age and cataract. This research led to the discovery of dihydrosphingomyelin, a major lens phospholipid. Dr. Borchman is also leading a group of research associates in studying the structure and interactions of the lipid tear film, which has yet to be fully described on a molecular level.