Observation with long follow-up of the first 200 cases of intraocular injection of silicone combined with vitrectomy led us to discover three major complications: cataract, keratopathy and hypertonia, the last two found only in aphakic eyes. No toxic action of silicone could be proved to explain these complications. They seem to be related to physical properties of the silicone which we use, and in particular its gravity lower than one. This density is responsible for noxious mechanical phenomena. They can be partially kept back by preserving the lens in the first stages, avoiding segmentary iridectomy in aphakic eyes, nocturnal procubitus position and silicone ablation in failed cases.