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Peter Ewen King-Smith, Kathleen Reuter, Heather L Chandler, Carolyn G Begley, Richard J Braun; On the structure of meibum spread on saline. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2254. doi: https://doi.org/.
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X-ray studies of Leiske et al., (2012, Biophys J 102, 369) show that human meibum contains crystalline or lamellar structures. Below 30oC, the main lamellar thickness was 4.9 nm, but a thickness of about 11 nm was stronger at higher temperatures. Rosenfeld et al. (2013, IOVS 54, 2720) interpreted these results in terms of localized “crystallites” but King-Smith et al. (2013, Ocul Surf 11, 236) proposed extended lamellae providing evaporation resistance, as in the skin lipid barrier. Here, high resolution color imaging was used to test for the presence of extended lamellae in meibum spread on saline.
Meibum was collected from 10 normal subjects in microcapillary tubes and pushed out using a fine wire onto a beaker of buffered saline at 40oC. Images of the meibum film were obtained as it cooled to room temperature, using a high resolution reflection microscope (King-Smith et al., 2011, Ocul Surf 9, 197). The beaker was mounted on a 3 dimensional positioning stage to adjust for focus and movement of the meibum. Temperature was measured by infrared thermometer to avoid contamination.
Typical findings for a 27 year old, white male, are shown in the figures. At 34oC meibum forms “lenses” within a dark “background”, b, Fig. 1A. Fig. 1B is the same image with much increased contrast, showing that the background contains darker areas, d; if these are from bare saline surface, then the lighter areas correspond to a thickness of about 6 nm by interferometric analysis. Fig. 1C shows that the dark areas constrict, probably from release of lipid from lenses. Below 30oC, the lenses start to grow “tails”, Fig. 2A. The thicknesses of these tails are multiples of 4.5 nm, indicating a multi-lamellar structure. Many lenses had completely converted into tails by 20oC, Fig. 2B, indicating that the tails contain all the material from the lenses.
Fig. 2C is an interpretation of the results. Above 30oC, a 6nm “background” layer spreads out from the lenses; this may correspond to polar lipids. We did not observe the 11 nm lamellae found by X-rays. Below 30oC, multi-lamellar “tails” spread out from the lenses; this may be non-polar lipid spreading on top of the polar background layer. The thickness of these lamellae of about 4.5 nm is similar to the X-ray value of 4.9 nm. The tails consist of extended lamellae rather than the localized “crystallites” of Rosenfeld et al.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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