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A. J. Bron, N. Yokoi, E. A. Gaffney, J. M. Tiffany; A Hyperosmolar Gradient in the Tear Meniscus: A Hypothesis to Explain Pathophysiological Events at the Lid Margin. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5199.
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Of all the body orifices that possess a mucocutaneous junction, only that relating to the eye is directly exposed to the atmosphere. We consider the consequent induction of osmotic gradients in the tear meniscus generated by evaporation and capillary flow and their likely pathophysiological effects on the eye.
A consideration of empirical data and mathematical modeling.
The concave meniscus thins progressively over the conjunctiva at the occlusal surface of the lid margin, just posterior to the point where it is pinned to the mucocutaneous junction (mcj). As a result, we predict that evaporation from the meniscus generates a gradient of osmolarity, which peaks at the apex of the meniscus towards the end of the interblink. Dilution of this effect by advection and diffusion of solute away from the meniscus apex is likely to be restricted by tear and surface mucins at this site and limited flow in the meniscus in the later part of the interblink. Mathematical modelling results will be presented.
We hypothesise that this creates a hyperosmolar region at the meniscus apex, which: i. reflexly triggers the onset of the blink, ii. encourages a high epithelial cell turnover at the mcj, iii. leads to surface epithelial immaturity and the line of mucosal staining behind the mcj referred to as Marx’s line, and iv, since the hyperosmolar mechanism will be amplified in dry eye, offers a means by which progressive lid margin damage could occur around the mcj. In keeping with this hypothesis, the sensitivity of the occlusal part of the marginal conjunctiva is similar to that of the central cornea, the region is highly innervated and stem cells on the lid margin are well placed to repair the implied physiological stress, in the waking state.
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