[Viscoelastic substances in cataract surgery. Principles and current overview].

The major aim for the application of viscoelastic substances in cataract surgery is prevention of corneal endothelial cell loss. This aim is fulfilled by deepening of the anterior chamber, mechanical endothelium protection against surgical trauma, absorption of ultrasound energy, and coating of intraocular lens. The first and mostly used viscoelastic in ophthalmic surgery is a 1% solution of sodium hyaluronate (NaHA) with a molecular weight of 4 million daltons, and a viscosity of 229,000 cP (Healon). For this substance, a good endothelium-protecting function in cataract surgery, especially phacoemulsification, is documented in the literature. In the meantime, further NaHA solutions of different concentrations and viscosities, and a mixture of chondroitin sulfate and NaHA are being offered, as well as low-viscosity solutions of hydroxypropylmethylcellulose (HPMC). The different rheological properties (viscoelasticity, viscosity, and pseudoplasticity) of the substances, the pertinent differences in surgical behavior (injectability, ease of aspiration and manipulation), and the viscoelastic side-effects (mainly IOP increase) are described.