Anyone who has experienced dry or weepy, watery eyes can confirm that tears alone aren’t enough to keep the eye from drying out. A microscopically thin film of oils called a ‘tear film lipid layer’ is key to preventing eye tears from evaporating and drying the eyes, or spilling out and down the cheeks. In a current issue of the Journal of Lipid Research, a group of Australian researchers have finally identified the unique structure of a key component of the tear film lipid layer that may lead to improved treatments for dry eye.
Although long-chain lipids (oils) make up only 5% of the tear film lipid layer, they play an important role in vision. Without them the lipid layer would resemble an oil slick floating atop a pool of water. “This clearly wouldn’t be satisfactory for you to look through,” states Stephen Blanksby, a professor at the Queensland University of Technology who led the research team in this study.
The unique properties of the tear film lipid layer derive from an oily substance called meibum that helps to contain eye tears between the eyeball and eye lids and to prevent evaporation.
Meibom is produced by dozens of tiny oil glands (meibomian glands) that line the upper and lower eyelids. Problems with meibomian glands can lead to dry eye, a condition associated with irritation, redness, discharge, and blurred vision. Dry eye symptoms can be mild and occasional, or severe and continuous, and may lead to scarring of the cornea without proper treatment.
Clogged meibomian glands can also lead to blepharitis, a chronic and difficult to treat condition marked by inflammation of the eyelids and red eyes. While blepharitis is unsightly and uncomfortable, it usually doesn’t cause permanent damage to eyesight, and it is not contagious.
Improving Treatment Options for Dry Eye
Prior to the new study, researchers knew that meibum was a unique lipid comprised of two fatty acids, but had no idea if they were joined end-to-end, or branched, an important distinction that conventional tests haven’t been able to answer.
Fortunately, Blanksby and colleague Todd Mitchell of the University of Wollongong have spent the last decade fine-tuning mass spectrometric techniques to characterize lipids. “We were able to bring a unique toolbox to bear,” said Blanksby. “Some of these techniques may not exist outside Todd’s and my laboratory.”
Using their new method allowed the researchers to determine that the most abundant of the ultra-long lipids are joined end-to-end. The team is now working with on methods to incorporate synthetic long-chain lipid as a component of drops for dry eye.
While knowledge of the lipid layer has expanded, according to Blanksby many eye drops still use mineral oil.
“This type of work provides a framework to produce a product that mimics, and is based on, the actual components that are present in human tears,” he said. He hopes that by creating a better match to the real tear film, blurriness and other side effects of using eye drops can be alleviated.
Source: Sarah E. Hancock, Ramesh Ailuri, David L. Marshall, Simon H. J. Brown, et.al. Mass spectrometry-directed structure elucidation and total synthesis of ultra-long chain (O-acyl)-ω-hydroxy fatty acids. Journal of Lipid Research, 2018; 59 (8): 1510 DOI: 10.1194/jlr.M086702