Shear flow characteristics of sodium hyaluronate. Relationship to performance in anterior segment surgery

In this study, methods were developed for the in vitro evaluation of the surgical performance characteristics of viscoelastic fluids, such as sodium hyaluronate (Healon). Sodium hyaluronate exhibited superior surgical performance to chondroitin-6-sulfate. The superior performance of sodium hyaluronate resulted in part from its high viscosity, which is 20 times greater than that of chondroitin-6-sulfate at shear rates on the order of 10 s-1. The gel-like character of sodium hyaluronate as evidenced by the creep flow behavior, was greater than that of chondroitin-6-sulfate and was important for maintaining depth in the anterior chamber. It was shown that a threshold of 80 poise for the shear viscosity (at approximately 10 s-1 was needed for useful performance in surgery. It was also shown that 0.42 USP units of hyaluronidase per 1.0 mg sodium hyaluronate produces a 90% decrease in the shear viscosity (at approximately 10 s-1) within approximately 2 1/2 hours. Use of sodium hyaluronate in conjunction with hyaluronidase would allow sodium hyaluronate to remain highly viscous during surgery, but would gradually become less viscous to facilitate aqueous outflow after surgery.