[Classification of visco-elastic substances for ophthalmologic surgery]

Individual properties of a viscoelastic substance for ophthalmologic applications are intimately tied to its chemical and rheologic characteristics. Independent comparative data for vicoelastic substances are not readily available or interpretable.

Twenty-six different commercially available viscoelastic substances were investigated using the Advanced Rheometric Expansion System and the Rheometric Scientific 800 device to analyze elastic and viscous modulus, complex viscosity (dynamic frequency dependance) and viscosity at the zero shear rate by extrapolation using the Ellis fit.

Viscosity (cps) at zero shear rate (s-1, mean of six different samples): Sodium hyaluronate products: Amivisc Plus: 128; AMO Vitrax: 41; Biolon: 243; Dispasan: 130; Dispasan Plus: 782; Healon: 243; Healon GV: 2451; Healon 5: 5525; Microvisc (Morcher Oil): 1162; Microvisc Plus: 3663; Morcher Oil: 1253; Provisc: 207; Rayvisc: 78; Viscoat: 58; Viscorneal (Allervisc): 733; Viscorneal Plus (Allervisc Plus): 1176; Visko: 206; Visko Plus: 1683. Hydroxypropylmethylcellulose (HPMC) products: Acrivisc: 7; Adatocel: 8; Coatel: 6; HPMC Ophthal H: 94; HPMC Ophthal L: 7; Ocucoat: 6; PeHa-Visko: 5; Visco Shield: 60.

Sodium hyaluronate as well as HPMC viscoelastic substances demonstrated remarkable differences in rheological properties from each other. In some cases, the results of this independent investigation differed from the values provided by the companies. A new division of commercially available viscoelastic substances into subgroups is presented, which provides a scientific base for various practical viscosurgical aspects. These real rheologic properties of each substance allow the ophthalmic surgeon to choose the viscoelastic substance that is most suitable for the surgical situation.