Abstract
Purpose :
The viscous properties of topical eye drops play an important role in the lubrication of the ocular surface. In the present study, we compared the shear-stress dependent viscous properties of high-molecular weight hyaluronic acid (HMWHA) versus low molecular-weight hyaluronic acid (LMWHA) combined with trehalose using a novel optical rheometer for accurate viscosity analysis of liquid samples. In addition, the viscosity of natural tears was studied.
Methods :
The measurements of viscosity were done using the Fluidicam RHEO technology (FORMULACTION, Toulouse France), a fully automated rheometer combining microfluidic and imaging technologies. Measurements were done at a shear rate range between 3000 s-1 to 30 000 s-1 in order to mimic the shear stress during eye blinking on the ocular surface. A HMWHA lubricant product (0.18% HA) was compared to a product containing LMWHA (0.15% HA) combined with trehalose (Thealoz Duo, Thea Pharma, Clermont Ferrand, France). In addition, natural tears as obtained from healthy subjects were used as comparator.
Results :
As expected for a non-Newtonian liquid, the natural tears showed almost no change in viscosity in response to changes in shear stress (natural tear viscosity was 0.91 mPa.s at 3000s-1, and 0.80 mPa.s at 30000 s-1). The hyaluronic-acid based eye drops had a higher viscosity compared to natural tears (p < 0.001). The LMWHA product containing trehalose showed a viscosity of 2.26 mPa.s at 3000 s-1 that decreased to 1.77 mPa.s at 30 000 s-1. The HMWHA product had the highest viscosity (p < 0.001 versus LMWHA product containing trehalose) of 4.73 mPa.s at 3000 s-1 decreasing to 2.44 mPa.s at 30 000 s-1. The decrease of viscosity with increasing shear rate was more pronounced for the HMWHA product (-48%) than for the LMWHA product containing trehalose (-20%).
Conclusions :
The present study confirms that neither natural tears nor the hyaluronic acid-based lubricants are Newtonian liquids. Combination of LMWHA with trehalose demonstrated a rheological behaviour closer to natural tears than the HMWHA product.
This is a 2021 ARVO Annual Meeting abstract.