By Linda Conlin, Pro to Pro Managing Editor
The ideal eye drop or contact lens will mimic the natural tear film, but tears are complex fluids with many components that may differ from person to person, and are affected by dry eye disease. Researchers at the American Institute of Physics analyzed tears at the micron level to investigate differences with individual symptoms of dry eye disease. (American Institute of Physics. "Breaking into tears with microrheology to design custom eye drops: New method reveals intricate behaviors of micron-sized particles in real, artificial tears." ScienceDaily. ScienceDaily, 11 July 2023.)
We think of tears as having three layers: lipid, aqueous, and mucus. But what makes up those layers? Tears contain lipids, carbohydrates, proteins, water, and salt, which can vary with dry eye disease. To determine how closely commercially available artificial tears are to human tears, researchers compared them using microrheology, which monitors the movement of micron-sized particles in liquids, using a technique that measures how light reflects off particles suspended in liquid to reveal how the liquid behaves in different scenarios, known as dynamic light scattering, or DLS. At this level, the team studied tear film properties such as viscosity (flow), elasticity and stability, and the effects of different concentrations of components in the liquids. They also tested the behavior of the liquids under stress, such as when the eye blinks.
The authors collected healthy human tears and tested 10 different formulations of artificial tears for comparison. Over 20 components have been identified in tear fluid, including water and salts (98.2%), lipids (600 different lipids of 17 classes), carbohydrates (glucose and glycosaminoglycans), a diverse range of proteins, and high molecular weight mucins. Human tears were found to have a viscosity that is 50% greater than that of pure water, comparable to artificial tears containing 0.1% hyaluronic acid. However, natural tears maintained peak viscosity ten times longer than artificial tears with the same initial viscosity. Study results also suggest that tear proteins may combine with other tear components to produce a collective effect on viscosity.
The authors plan to continue to explore more complex formulations of artificial tears and extend their work to the study of human tears with different pathologies. "Through careful tuning, artificial tears can be tailored to meet specific needs, such as stability, lubrication, and moisturization, and mimicking natural tears," lead author Juan F. Vega said. "Ultimately, this work aims to enhance the comfort and well-being of individuals experiencing dry eye symptoms." The study highlights the importance of understanding the properties of biopolymer solutions for the design and optimization of artificial tears and potentially other related systems.
