Differences in Meibum and Tear Lipid Composition and Conformation.

Area of Science:

• Ophthalmology
• Biochemistry
• Materials Science

Background:

• Meibum and tear lipids play crucial roles in maintaining ocular surface health and tear film stability.
• Understanding the structural and compositional differences between meibum and tear lipids is essential for diagnosing and treating dry eye disease.

Purpose of the Study:

• To investigate the compositional and structural differences between tear lipids and meibum lipids.
• To explore the relationship between lipid structure and tear film stability, particularly in patients with meibomian gland dysfunction and dry eye.

Main Methods:

• Infrared spectroscopy was used to analyze the lipid composition and structure of tear lipids (TLHSCT) and meibum (MHSCT) from patients undergoing hematopoietic stem cell transplantation.
• Meibum from donors with (MMGD) and without (Mn) meibomian gland dysfunction were analyzed.
• The relative content of CH3 and CH2 moieties and the presence of double bonds were quantified using the infrared CH stretching region.

Main Results:

• Meibum from MHSCT and MMGD patients exhibited 18% fewer CH3 moieties compared to Mn.
• Tear lipids (TLHSCT) showed approximately 20% greater phase transition temperature, cooperativity, and order compared to MHSCT.
• Both MHSCT and TLHSCT contained fewer double bonds compared to Mn and MMGD.

Conclusions:

• Tear lipids possess a higher degree of order than meibum lipids, potentially affecting tear film function.
• The hydrocarbon order of lipids, influenced by CH3/CH2 ratio and saturation, may serve as a biomarker or contributing factor to tear film instability in conditions like meibomian gland dysfunction and dry eye.
• Lipid hydrocarbon order is associated with younger age, meibomian gland dysfunction, and dry eye post-hematopoietic stem cell transplantation.