Douglas Borchman
University of Louisville, USA
Posters & Accepted Abstracts: J Clin Exp Ophthalmol
Dry eye affects over six million people in the United States. Tears become more unstable with age and meibomian gland dysfunction (MGD). Changes in the composition, and structure of a thin film of lipid on the surface of tears called the �tear film lipid layer� (TFLL) may cause tears to become more unstable. In this study NMR spectroscopy was used to measure TFLL composition. Infrared, Raman and Brewster angle spectroscopies were used to measure the structure of the TFLL. Langmuir trough technology was used to measure TFLL rheology. Several abnormalities in the TFLL composition were identified that may contribute to TF instability including terpenoids, saturation, protein and cholesteryl esters. When terpenoid levels in TFLL are low as in MGD, the TF is unstable and patients have the signs and symptoms of dry eye. When terpenoids are restored with azithromycin treatment, TF stability is restored and patients no longer have the signs and symptoms of dry eye. A more saturated TFLL contributed to TF stability. The TFLL phase transition temperature and hydrocarbon chain decrease with increasing age. It is reasonable that stronger lipid-lipid interactions could stabilize the tear film since these interactions must be broken for tear breakup to occur. Meibum is fluid enough to be expressed from the meibomian glands and becomes more ordered (viscous) on the surface of the eye. A stiff ordered molecular arrangement results in a more elastic TFLL in which molecules are able to rearrange during the compression and expansion of a blink.
