Dry eye disease in astronauts: a narrative review.

Long-duration spaceflight can have adverse effects on human health. One of the most common ocular conditions experienced by astronauts is dry eye disease (DED). Symptoms of DED include feelings of eye irritation, eye strain, foreign body sensation and blurred vision.

Effects on the Human Tear Film of Applying Skin Lipids to the Ocular Surface.

Purpose: The effect of skin lipids on the formation and stability of the human tear film was investigated.

Methods: Skin swab substances (SSSs) were applied to the eyes of volunteers and studied using fluorescein or with TearView, which records infrared emissivity showing tear film integrity in real time. Results were compared with similar experiments using castor oil, freshly collected meibum, or acetic acid, which simulated the low pH of the skin.

Novel Nano-Liposome Formulation for Dry Eyes with Components Similar to the Preocular Tear Film.

Dry eye is commonly treated with artificial tears; however, developing artificial tears similar to natural tears is difficult due to the complex nature of tears. We characterized and evaluated a novel artificial tear formulation with components similar to the lipid and aqueous constituents of natural tears. Nano-liposomes, composed in part of phosphatidylcholine, were dispersed in an aqueous solution of bioadhesive sodium hyaluronate.

An Experimental Model to Study the Impact of Lipid Oxidation on Contact Lens Deposition In Vitro.

Purpose: This study was to establish a controlled in vitro test system to study the effect of lipid oxidation on lipid deposition on contact lenses.

Methods: Fatty acids with varying degree of unsaturation were oxidized using the Fenton reaction. The degree of lipid oxidation and the lipid moieties formed during the oxidation were identified and estimated by various lipid staining techniques following separation with thin-layer chromatography, and by measuring thiobarbituric acid reactive substances or peroxides in solution.

Negative Ions in Space.

Until a decade ago, the only anion observed to play a prominent role in astrophysics was H. The bound-free transitions in H dominate the visible opacity in stars with photospheric temperatures less than 7000 K, including the Sun. The H anion is also believed to have been critical to the formation of molecular hydrogen in the very early evolution of the Universe.

Using Biotinylated Proteins to Demonstrate Immunodetection of Antigens via Western Blotting, Dot Blots, and Immunohistochemistry.

Using biotinylated targets for detection by enzyme-linked avidin allows immunodetection methods to become more economic in cost and time as it negates the need for a specific primary antibody. Methods are described to use exogenously added biotin to complex biological samples to demonstrate western blotting, dot blots, and immunohistochemistry. These methods can be used in biological science tertiary teaching laboratories to allow novices to gain skills in a risk-free environment to promote student motivation and engagement.

The real reason for having a meibomian lipid layer covering the outer surface of the tear film - A review.

This review critically evaluates a broad range of literature in order to show the relationship between meibum, tear lipids and the tear film lipid layer (TFLL). The relationship of meibum composition to dry eye syndrome is briefly discussed. The review also explores the interactions between aqueous and the TFLL by examining the correlations between meibomian lipids and lipids extracted from whole tears, and by considering protein adsorption to the TFLL from the aqueous.

The tachykinin peptide neurokinin B binds copper(I) and silver(I) and undergoes quasi-reversible electrochemistry: towards a new function for the peptide in the brain.

The tachykinin neuropeptide family, which includes substance P and neurokinin B, is involved in a wide array of biological functions. Among these is the ability to protect against the neurotoxic processes in Alzheimer's Disease, but the mechanisms driving neuroprotection remain unclear. Dysregulation of metal ions, particularly copper, iron and zinc is a common feature of Alzheimer's Disease, and other amyloidogenic disorders.

Tear film stability: a review.

Tear film stability can be assessed via a number of tools designed for clinical as well as research purposes. These techniques can give us insights into the tear film, and allow assessment of conditions that can lead to dry eye symptoms, and in severe cases, to significant ocular surface damage and deterioration of vision. Understanding what drives tear film instability and its assessment is also crucial for evaluating existing and new therapies.

An investigation of the likely role of (O-acyl) ω-hydroxy fatty acids in meibomian lipid films using (O-oleyl) ω-hydroxy palmitic acid as a model.

(O-acyl) ω-hydroxy fatty acids (OAHFAs) are a recently found group of polar lipids in meibum. Since these lipids can potentially serve as a surfactant in the tear film lipid layer, the surface properties of a molecule of this lipid class was investigated and compared with a structurally related wax ester and a fatty acid. (O-oleyl) ω-hydroxy palmitic acid was synthesized and used as the model OAHFA.

Interfacial dilatational viscoelasticity of human meibomian lipid films.

Purpose/aim: The meibomian lipid layer is able to withstand the enormous stresses and deformations that occur during blinking due to the combination of its elastic and viscous properties. The purpose of this study was to measure the dilatational viscoelasticity of in vitro meibomian lipid films and compare how these properties differ between room temperature and physiological temperatures. Viscoelasticity was also compared with meibomian lipid films seeded with cholesterol or β-carotene (the levels of these lipid species change in disease states).

Effects of keratin and lung surfactant proteins on the surface activity of meibomian lipids.

Purpose: In vitro studies indicate that surface tension and surface viscosity of the tear film lipid layer (TFLL) are governed by interactions between meibomian lipids and proteins from the aqueous layer. The role of minor tear proteins with strong lipophilic properties or those correlated with pathological states is still unknown. The discovery of lung surfactant proteins (SPs) in tears and keratin in normal and abnormal meibomian gland excretions warrants investigation into their effects on the surface activity of meibomian lipid films.

Lipid component contributions to the surface activity of meibomian lipids.

Purpose: Meibomian lipid films have very complex physical properties that enable them to be compressed and expanded without collapsing. These properties can be attributed to the self assembly of the individual components, mainly wax and cholesteryl esters (WE and CE). Here, the surface pressure properties of WEs and CEs films have been compared to evaluate their contributions to meibomian lipid films.

The use of biotin to demonstrate immunohistochemistry, Western blotting, and dot blots in university practical classes.

Immunological detection of proteins is an essential method to demonstrate to undergraduate biology students, however, is often difficult in resource and time poor student laboratory sessions. This method describes a failsafe method to rapidly and economically demonstrate this technique using biotinylated proteins or biotin itself as targets for detection. This negates the need for a specific primary antibody, saving cost and time.

Analysis of Comparison of Human Meibomian Lipid Films and Mixtures with Cholesteryl Esters In Vitro Films using High Resolution Color Microscopy.

Purpose: The lipid layer of the tears has been studied in vivo using high resolution color microscopy (HRCM). The purpose of these experiments was to gain further insight into the structure of the lipid layer by applying HRCM to in vitro meibomian lipid films.

Methods: Films of human meibomian lipids, cholesteryl nervonate, cholesteryl palmitate, or their mixtures, were spread on a Langmuir trough.

Divalent cations in tears, and their influence on tear film stability in humans and rabbits.

Purpose: Reduced tear film stability is reported to contribute to dry eye. Rabbits are known to have a more stable tear film than humans. Thus, we sought to examine the tears of rabbits and humans for metal cations, and to test how they influence tear film stability.

Barriers to clinical uptake of tear osmolarity measurements.

Aim: The aim of the study was to examine the possibilities of measuring tear osmolarity in a general clinical setting, and to identify the barriers preventing the uptake of new methodologies for its measurement.

Methods: Five non-contact-lens wearers were recruited to evaluate the diagnostic capability of the TearLab. Three osmolarity measurements were taken at 1 min intervals in the morning at 09:00, midday between 12:00 and 13:00 and afternoon at 16:00 for two consecutive days.

Surfactant properties of human meibomian lipids.

Purpose: Human meibomian lipids are the major part of the lipid layer of the tear film. Their surfactant properties enable their spread across the aqueous layer and help maintain a stable tear film. The purpose of this study was to investigate surfactant properties of human meibomian lipids in vitro and to determine effects of different physical conditions such as temperature and increased osmolarity, such as occur in dry eye, on these properties.

Nanoscale phase dynamics of the normal tear film.

The tear film is a dynamic multilayered structure. The interactions and the interfacial dynamics between the layers that occur during a blink cycle must be such that they allow for maintenance of a stable tear film. Attempts to understand these dynamics have been limited by the techniques and biomarkers used.

The interfacial viscoelastic properties and structures of human and animal Meibomian lipids.

As the interface between the aqueous layer of the tear film and air, the lipid layer plays a large role in maintaining tear film stability. Meibomian lipids are the primary component of the lipid layer; therefore the physical properties of these materials may be particularly crucial to the functionality of the tear film. Surface pressure versus area isotherms, interfacial shear and extensional rheology, and Brewster angle microscopy (BAM) were used to characterize the Meibomian lipids from different species known to have different lipid compositions.

The effect of Meibomian lipids and tear proteins on evaporation rate under controlled in vitro conditions.

The lipid layer of the tear film is associated with preventing evaporative loss. The ability of human Meibomian lipids to reduce evaporation in vitro was tested. Films of human or animal Meibomian lipids or mixtures of cholesterol and phosphatidylcholine were spread on the surface of either artificial buffer or on whole tears and placed on a mass balance that was enclosed in a sealed chamber.