Abstract
Purpose::
To test the possible detrimental effect of a free fatty acid (oleic acid, OA) on the surface pressure/tension behavior of a lipid layer formed of meibomian gland secretions (MGS).
Methods::
A Langmuir miniature film balance with two coupled barriers and a pressure sensor was used to perform analysis of the surface tension properties of human MGS in vitro. Two aqueous subphases were used. The first subphase consisted of phosphate buffered saline solution (PBS, 0.9% NaCl, pH 7.4). The second one in addition to PBS included 20 to 50 uM of oleic acid. An aliquote of MGS dissolved in chloroform was spread onto the surface of the subphase, after chloroform evaporated multiple isotherms were recorded.
Results::
When the first subphase was used, MGS formed a stable lipid layer and the isotherms showed a high degree of reproducibility. When the subphase containing OA was used, there was a dramatic change in the spreadability and in the surface pressure/tension of meibum. This subphase caused a complete collapse (or prevented formation) of the otherwise stable lipid layer.
Conclusions::
This experiment confirmed our earlier hypothesis of the detrimental effects of free fatty acids on the stability of the tear film lipid layer in vivo and on the MGS in vitro. It also suggests a mechanistic explanation of our earlier observations that antibiotics of the tetracycline family, which inhibit lipases, are effective in the management of patients with meibomianitis in that they lead to a decrease in free fatty acids (e.g. OA) concentration in MGS.
Keywords: cornea: tears/tear film/dry eye