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Georgi Asenov Georgiev, Norihiko Yokoi, Slavyana Ivanova, Vesselin Tonchev, Rumen Krastev, Zdravko Lalchev; Investigation of Surface Properties of Films of Human Meibum from Normal Eyes and from Eyes with Meibomian Gland Dysfunction. Invest. Ophthalmol. Vis. Sci. 2014;55(13):37.
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© ARVO (1962-2015); The Authors (2016-present)
Meibomian gland dysfunction (MGD) is considered as one of the major causes for evaporative dry eye. Thus to characterize the difference of surface properties of meibomian lipids (ML) between normal eyes (nML) and eyes with MGD (dML) is of key importance to understand the molecular mechanisms of the disease.
ML were collected from eyes of 7 normal subjects (22-73 years old; mean age 42.7±7.5) and eyes of 7 MGD patients (64-82 years old; mean age 73.5±2.5). MGD was diagnosed based on dry eye symptoms, abnormalities around meibomian gland orifices (mucocutaneous junction or lid margin), obstructive findings of the orifices and decreased expressibility of meibum. Fluorescein breakup time, Schirmer I test and scoring of ocular surface epithelial damage were also measured. The ML samples were spread at the air/phosphate buffered saline interface and the resultant films were examined in vitro at blink-like compression/expansion of the film area by Langmuir surface balance. The sample’s lateral elasticity and capability to compress and spread during dynamic area changes were evaluated through the surface pressure-area isotherms and isocycles. The surface dilatational rheological properties of ML were probed in the frequency range 1-10-5 Hz via the step/relaxation method. The lipid films morphology was monitored by Brewster Angle Microscopy. All the samples were evaluated both at 25 and 34°C.
Statistically significant difference (P<0.05) was found in the rheological properties of the samples with dML showing slow viscous dominated relaxation process at 10-3-10-4 Hz, while nML remained mainly elastic. Brewster angle microscopy revealed that nML showed better spreading at the air/saline interface while dML films were non-uniform and patchy. The isotherm reversibility (i.e. hysteresis) of lipid films revealed significant interindividual variability and was strongly dependent on the film thermal history.
Our study suggests that dML have worsened viscoelasticity and spreading at the air/water interface compared to nML. Hence the surface properties of meibomian lipids could serve as a reliable functional marker for diseased meibum samples. The results correlate with the literature data on decreased amount of polar lipid ((O-acyl)-ω-hydroxy fatty acids) and cis-double bonds in dML.
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