In conclusion, one can state that silicones are one of the most inert materials available for use in medical field today. They meet all the requirements for implants, summarized in table V, and can be considered as the ideal material for intraocular use, provided that the polymer is absolutely pure and free of any kind of residues. For silicone rubbers the following specifications have to be fulfilled: the material has to be free of reactive prepolymers and of catalyzers, the filler should be of the same chemical nature as the basic material and should be chemically bound to the backbone of the polymer, to avoid any kind of migration out of the polymer. For silicone oils, the following criteria are desirable: the oil has to be practically free of low molecular components, mainly cyclohexanes, the molecular weight distribution should be as small as possible and the oil should be free of catalysts.