It will be difficult to find an ophthalmic surgeon who will gladly do his work entirely without viscoelastics. Within just a few years this group of substances has enlarged the field of ophthalmic surgery enormously. Many procedures have be- come safer and simpler and other techniques could only be developed because of the availability of visco elastics. Especially cataract surgery and implantation of intraocular lenses have benefitted. Implantation of an intraocular lens can be per- formed much more reliably into the capsular bag without endangering the posterior capsule. Implantation of foldable lenses would be almost impossible without visco elastics. However, other surgical maneuvers also necessitate visco- elastics, especially when the anterior chamber must be maintained, the corneal endothelium must be protected and delicate tissues must be manipulated. A cor- neal transplant can be sutured safely into the recipient corneal ring using visco- elastics. Even in glaucoma surgery, visco elastics gain importance as they are being used in trabeculectomy or in deep sclerectomy with additional viscocana- lostomy. But which substance is best for which purpose? Just as much as a basic phar- macological knowledge is necessary for a rational use of drugs, in-depth know- ledge of physicochemical properties and objective investigations are prerequi- sites for a logical selection of visco elastics from an ever increasing number of available substances. H.