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Juan C. Arciniega, Erfan J. Nadji, Igor A. Butovich; Effects of Calcium and Magnesium on Meibomian Lipid Films In the Presence and Absence of Oleic Acid. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3729.
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The purpose of this study was to evaluate, using a Langmuir trough and a Brewster angle microscope, the impact of Ca2+ and Mg2+ on meibomian lipid films in the presence and absence of oleic acid.
Normal human meibum samples were soft-expressed from eyelids of healthy, non-dry eye volunteers. Sample dry weights were determined gravimetrically and then dissolved in CHCl3. A predetermined amount of meibum was spread onto the surface of Tris-buffered saline (TBS) aqueous solution subphase in the Langmuir trough to form a meibomian lipid film (MLF). Three series of TBS were used: 1) TBS containing no divalent cations; 2) TBS with physiological concentrations of either Ca2+ or Mg2+ (0.14 mg/ml each), and 3) TBS with either Ca2+ or Mg2+ at 0.42mg/ml. Varying amounts of oleic acid (OA), 0 to 30µM, were dissolved in TBS (TBS-OA). Multiple π/A isotherms were recorded in cycles for each sample using a thermostated Langmuir film balance, and analyzed for rheological parameters such as rigidity, elasticity, and hysteresis. A Brewster angle microscope (BAM) was used for MLF visualization.
When studied at the normal corneal temperature of 34°C, in the absence of OA, meibum formed stable, non-collapsible films regardless of the amount of Ca2+ or Mg2+ dissolved in the subphase. In the absence of Ca2+, OA dissolved in TBS, quickly disrupted the MLF. This effect was visible at OA concentrations of 2.5µM or higher. In the presence of the physiological Ca2+ concentration, the effects of OA on MLF were small regardless of the OA concentration. The protective effect of Ca2+ was found to be concentration-dependent, increasing from 0.14mg/ml to 0.42mg/ml. BAM microphotographs revealed dramatic changes in the structure of the MLF in the presence of 30 µM OA, and also illustrated the protective effect of 0.14 mg/ml Ca2+ (Figure).
The harmful effect of OA on the MLF is diminished in the presence of physiological concentration of Ca2+.
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