A new study sheds some light on the complex design of tears. What we think of as tears, scientists call tear film, which is made up of three distinct, microscopic layers. The middle, watery layer – what we normally think of as tears when we cry – is sandwiched between a layer of mucus and an outer layer of fatty, oily substances collectively called meibum.
It's in this outer layer that researchers describe, for the first time, a new class of lipids – a type of fat – that make up part of the film. They also identified one of these lipids, oleamide, which had not been known to be a part of tears before.
With each blink, meibum spreads over the surface of the eye. It keeps the watery middle layer in place, ensuring that our eyes stay moist.
Finding these lipids may help scientists better understand the causes of eye-related disorders such as dry eye disease, which affects anywhere from 12 to 14 million Americans, said Kelly Nichols, the study's lead author and an assistant professor of optometry at Ohio State University.
“The lack of certain compounds in the tear film may result in a number of different eye-related disorders, including dry eye,” she said. “The amount of oleamide and related lipids in tear film may be related to these disorders.”
Dry eye is really a collection of irritating symptoms that includes microscopic damage to the front of the eye. The eyes may ache, burn, feel extremely dry or excessively tear.
The researchers report their findings in the current issue of the journal Investigative Ophthalmology and Visual Science.
They collected oily meibum secretions from the meibomian glands of healthy volunteers. The meibomian glands are tiny, grape-like clusters of cells that line the rim of our upper and lower eyelids – the outlets to these glands are roughly adjacent to the eyelashes. Researchers gently pressed the volunteers' lower eyelids and collected droplets of meibum in tiny glass tubes.
The researchers examined the meibum samples in the laboratory. They used a technique called electrospray mass spectrometry to differentiate between the different lipid components. This technique adds an electric charge to microscopic droplets of the oily substance, which allows the instrument to detect different components based on electrical charges and mass.
Nichols points out that researchers have used other techniques, such as chromatography, to characterize types of lipids in the tear film, but advances in mass spectrometry technology are improving research efforts.
“Other scientists used different techniques to try to determine the composition of meibum, but mass spectrometry is sensitive enough to detect individual lipid molecules, like oleamide,” Nichols said.
Oleamide was first identified as a lipid in the brain, where one of its roles is to induce sleep. It also has other key functions throughout the central nervous system. But the current study is the first to find and describe oleamide and related lipids in tear film.
“The finding could give us more insight into the role of lipid activity in humans and may also indicate a new function for oleamide and related lipids in cellular signaling in the eye and in the maintenance of tear film,” said Nichols, adding that researchers don't fully understand the function of oleamide, or the other lipids in the meibum.
“Oleamide appears to be a predominate lipid in tear film,” she said. “It's there for a reason, but we're not sure yet what that reason is.”
Nichols and her team are currently studying the role of oleamide in cellular signaling and communication in the eye, along with the role that the lipid may play in dry eye.
“Dry eye is really a disorder of symptoms that irritate the eyes,” Nichols said. “Not everyone with dry eye responds to the same treatment. If we could find individuals with varying oleamide levels, then we may be able discern one cause of dry eye, and specifically treat that.
“Even though two people with dry eye may have the same symptoms, there may be very different causes underlying those symptoms.”
Nichols conducted the study with Ohio State colleagues Jason Nichols, assistant professor of optometry; Corrie Ziegler, a graduate student in optometry; Kari Green-Church, a research scientist with the Mass Spectrometry and Proteomics Facility; and Bryan Ham, a postdoctoral researcher at the Pacific Northwest National Laboratory in Richland, Wash.
Kelly Nichols | EurekAlert!
First form of therapy for childhood dementia CLN2 developed
25.04.2018 | Universitätsklinikum Hamburg-Eppendorf
Do microplastics harbour additional risks by colonization with harmful bacteria?
05.04.2018 | Leibniz-Institut für Ostseeforschung Warnemünde
Magnetic resonance imaging, or MRI, is a widely used medical tool for taking pictures of the insides of our body. One way to make MRI scans easier to read is...
At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.
Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
26.04.2018 | Power and Electrical Engineering
26.04.2018 | Life Sciences
26.04.2018 | Power and Electrical Engineering