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Silicone oils (polymethylsiloxanes) with different viscosities (200, 1000 and 5000 cSt) and a fluorinated silicone oil (5000 cSt) were injected into the peritoneum of CBA mice. Three weeks after the injection, peritoneal exudates were obtained and investigated using light and electron microscopy. For each silicone-oil type, light-microscopic examination revealed the presence of abundant extracellular lipid-like droplets and a dense cellular infiltrate composed of macrophages, lymphocytes and multinucleated giant cells. Lipid-like inclusions were observed in macrophages and multinucleated giant cells. These intracellular inclusions were revealed to be membrane bound by transmission electron microscopy. We observed no differences with respect to the amount of phagocytotic activity for the different silicone-oil types tested. Purified silicone oils of lower viscosity (OP 200 and OP 1000) resulted in the mildest chronic inflammatory reaction. Our results suggest that emulsification, phagocytosis and granulomatous inflammation are associated with intraocular silicone-oil implantation. The question of which properties would make a silicone oil most suitable for clinical use requires further investigation.

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