Biophysical and Morphological Evaluation of Human Normal and Dry Eye Meibum Using Hot Stage Polarized Light Microscopy

Abstract

HSPM is an effective tool that is suitable for biophysical and morphological evaluation of meibum. Morphological properties and melting characteristics of human meibum were found to be similar to those of mice. Abnormal meibum of many dry eye patients contained large quantities of nonlipid, protein-like inclusions, which were routinely absent in meibum of normal controls.

TFOS DEWS II Tear Film Report

“…Monolayers of tear film-like wax esters can retard evaporation when used at temperatures 3 °C lower than their bulk melting temperature [258,260,261]. However, meibum has a much more complex composition, structure and thermotropic behavior compared to the model films, and the melting temperature of meibum (~30 °C) [262–264] is lower than the ocular surface temperature (35 °C). Recently in vitro studies with the Interfacial Dewetting and Drainage Optical Platform (i-DDrOP) on silicone hydrogel (SiHy) contact lenses have shown that the mucoaqueous subphase beneath thinner parts of meibomian films thins and dewets faster compared to that seen below thicker “islands” in the meibomian layer [265].…”

“…Data on the thermotropic phase transitions (via spectroscopy, differential scanning calorimetry and X-ray diffraction studies) [262,264,301–303] and interfacial and bulk rheology [29,301,302] of tear lipids in vitro and in vivo , suggest a thick viscoelastic duplex structure composed of a monomolecular layer of amphiphilic polar lipids at the mucoaqueous surface and a generally unstructured shear thinning lipophilic suspension at the lipid-air interface. The lipophilic suspension consists of lipid lamellar-crystallite particulates immersed in a continuous liquid phase with no long-range order.…”

Analysis of the Pathogenic Factors and Management of Dry Eye in Ocular Surface Disorders

“…As a consequence of this increased enzyme activity, the bacteria change meibum's viscosity, leading to further stagnation of meibum within the MGs and generating free fatty acids, which in turn cause inflammation and hyperkeratinization [4,7]. This change of the lipid composition lead to the appearance of foam in the tear film, often visible on the eyelid margin of patients with MG dysfunction [8,9]. The absence of the normal meibum also would reduce the lipid content of the tear film, entering in the vicious circle of DE disease, in which 5 the lipid deficiency of the tear film promotes increased tear evaporation, hyperosmolarity, and inflammation.…”

Proteolytic activity in the meibomian gland: Implications to health and disease

“…How proteolytic activity affects the maturation process of sebocytes and, consequently, the composition and accumulation of cytoplasmic lipids, is still poorly understood. At the protein level, large quantities of nonlipid, protein-like inclusions have been detected in the meibum of patients with dry eye (Butovich et al, 2014). However, it is unclear whether proteases, reported in the facial sebum of patients with acne, are present in meibum, and whether they play a role in the pathophysiology of ocular surface disease.…”

“…Research during the last decade has led to the identification of key regulatory mechanisms critical to maintenance of the integrity and function of the meibomian gland and its alteration in pathological conditions. These advances have been facilitated by the development of novel imaging and analytical methods that allow the structural assessment of the meibomian glands during ocular surface disease and aging (Butovich et al, 2014; Fasanella et al, 2016; Parfitt et al, 2012). Furthermore, a better understanding of the biology of the meibomian gland and the tear lipidome is fueling advances in the identification of biomedical targets and potentially novel therapeutic approaches (Butovich, 2013; Parfitt et al, 2016a; Parfitt et al, 2016b).…”