Purchase this article with an account.
J. C. Arciniega, J. C. Wojtowicz, E. M. Mohamed, I. A. Butovich; Effects of Ceramides on Meibomian Lipid Layers in vitro. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6284.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The outermost layer of the tear film is formed of lipid-rich excreta called meibum. The tear film lipid layer (TFLL) is thought to protect the corneal epithelium from the evaporation of the aqueous layer. Changes in the composition of the TFLL can alter its properties and subsequently compromise its integrity. Earlier analyses detected an increased amount of ceramides (Cer) in meibum lipids of patients with meibomian gland dysfunction, possibly due to the abnormal hyperkeratinization of the meibomian gland ducts. It has also been suggested that Cer could have a destabilizing effect on tear film. However, no quantitative data on this putative destabilizing effect of Cer has ever been reported. The aim of our in vitro study was to quantitatively evaluate the direct effects of Cer on the biophysical properties of meibomian lipids layers.
Meibum samples were collected from the meibomian glands of healthy volunteers. Their dry weights were determined gravimetrically. A thermostated Langmuir film balance was used to study the surface pressure area (π/A) isotherms of meibum. A series of mixed solutions of bovine brain Cer (from Sigma Chem. Co, St. Louis, MO) and meibum dissolved in CHCl3 at different weight ratios (10:0, 8:2, 6:4, 4:6, 2:8 and 0:10, respectively) were spread onto the surface of the Tris-buffered saline aqueous subphase to form lipid layers. After evaporation of the solvent, multiple π/A isotherms were recorded in cycles.
Studied at a physiological corneal temperature of 34°C without Cer, meibum layers remained stable and non-collapsible at any surface pressure and tested temperature. Under the same conditions, the Cer layers collapsed at a surface pressure of about 45mN/m and had lower elasticity compared to meibum. Increasing Cer to meibum ratios in the mixtures had a strong impact on the stability of the human meibum films. Using the sample solutions with Cer to meibum ratio of 4:6 or above, the lipid layers abruptly collapsed at about 40 mN/m. The extent of collapsing was proportional to the Cer to meibum ratio used.
When Cer are present in meibum in sufficient quantities, the π/A isotherms of meibum are strongly affected. Our findings suggest that Cer decrease the stability and elasticity of the TFLL causing its collapsing. However, it remains to be seen if Cer in meibum of dry eye patients can reach the threshold level that would be high enough to have a detrimental effect on the stability of the TFLL in vivo.
This PDF is available to Subscribers Only