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Senior ophthalmologists with years of surgical experience have performed thousands of cataract surgeries and often know what they want from an ophthalmic viscosurgical device.
The reality of OVD rheologic diversity has led some surgeons to begin to use more than one OVD during their procedures, catering their choice of viscoelastic to different stages of surgery and possible complications. To follow the growing use of two separately packaged products and provide surgeons with a more convenient alternative, OVD manufacturers began to offer dual-syringe products, beginning in the late 1990s with a combination system (DuoVisc, which is 1% sodium hyaluronate [ProVisc] and 4% sodium chondroitin sulfate–3% sodium hyaluronate [Viscoat], Alcon Laboratories).
One way to maximize the potential of each type of OVD and facilitate efficient and successful surgery is to understand the basis of how OVDs are classified.
Modern OVD classification is based on the zero-shear viscosity (the viscosity of a liquid at rest) and the cohesion-dispersion index (CDI). CDI is the percentage of viscoelastic solution aspirated per 100 mm Hg vacuum pressure (typically measured at a 80º phaco tip insertion angle)1 and can range from less than 5% for the most dispersive OVDs to more than 70% for the most cohesive OVDs.
The appeal of two-syringe products is that they package a high-CDI cohesive agent, such as 1% sodium hyaluronate (Healon, Abbott Medical Optics [AMO]; CDI = 31.2 or ProVisc, Alcon Laboratories; CDI = 46),1 with a low-CDI dispersive agent, such as 4% sodium chondroitin sulfate–3% sodium hyaluronate (Viscoat, Alcon Laboratories; CDI = 3.4), to enhance the accessibility of complementary viscoelastics during a single operation.
In the past few years, however, the viscoadaptive 2.3% sodium hyaluronate (Healon5, AMO; CDI = 22) and the viscous dispersive 4% sodium chondroitin sulfate–1.6% sodium hyaluronate (DisCoVisc, Alcon; CDI = 12) have challenged the versatility of dual-syringe systems by offering many of the features of both types of OVDs in a single syringe.