The viscosity of highly concentrated hyaluronic acid (HA) may increase the friction on soft contact lenses (SCLs) and potentially damage the ocular surface, according to a study published in Eye & Contact Lens.
Researchers conducted an analysis to determine whether HA increases friction between contact lenses and the ocular surface due to its viscosity. They used a modified pendulum-type friction tester to measure the coefficient of friction (CoF) of 3 types of SCL materials; narafilcon A, delefilcon A, and etafilcon A with polyvinylpyrrolidone (PVP). Investigators diluted HA with distilled water to obtain 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% concentrations (wt/vol). They measured friction by placing the lenses in each lubricant, and suspending them from the pendulum’s fulcrum. A video recorder measured changes in position on a protractor scale after the pendulum was released from a 30° inclination. They performed each measurement 10 times with each lubricant, and contact lenses were replaced for each trial.
Under a low concentration (0.05%) of HA, the CoF of the narafilcon A and delefilcon A lenses (0.032±0.003 and 0.032±0.002, respectively) were significantly lower than in saline (0.037±0.02 and 0.038±0.004, respectively, P <.05). Under higher concentrations (0.3%, 0.4%, and 0.5%) of HA, the CoF was significantly higher than saline (P <.01) in all three SCLs. The research team reported no significant differences in CoF among saline and all concentrations of HA (P >.05), and noted that HA viscosities increased exponentially with concentration
“The current study found that the CoFs of SCLs decreased with a low HA concentration but increased with higher HA concentrations,” according to the investigators. “If there are no differences in the effectiveness among the HA concentrations for treating dry eye, it may be better to use an eye drop with a low HA concentration for CL wearers to relieve the dry eye symptoms of contact lens discomfort (CLD).”
Study limitations include the use of only 2 types of silicone hydrogel and 1 type of hydrogel SCL material, and the inability to use the pendulum-type friction tester for long-term measurements.
Iwashita H, Mabuchi K, Itokawa T, Okajima Y, Suzuki T, Hori Y. Evaluation of the lubricating effect of hyaluronic acid on contact lenses using a pendulum-type friction tester under mimicking physiological conditions. Eye Cont Lens. 2022;48(2):83-87. doi:10.1097.ICL.0000000000000853