Heavy silicone oil: a "novel" intraocular tamponade agent

Advances in vitreoretinal surgery have greatly increased the anatomical re-attachment rate in cases with proliferative vitreoretinopathy. Intraocular tamponade agents have been in use by vitreoretinal surgeons for nearly a century. The effectiveness of an internal agent relies on its ability to make contact with the internal surface of the vitreous cavity. In the short term, this is controlled by the agent's specific gravity and interfacial tensions. In the long term, the viscosity of the material is critical to maintaining its integrity and thus reducing dispersion. The commonly used tamponade agents such as perfluoropropane (C3F8), sulfur hexafluoride (SF6), and silicone oil are "lighter than water" hence, float upward in the aqueous. A consequence of this is that in the upright position the superior retina is very well supported, leaving the inferior retina less well so. More recently, there has been interest in the development of "heavier than water" long-term tamponade agents that sink in the eye. Heavy silicone oil is a transparent, homogenous solution of two substances used as a single tamponade agent with improved properties and a specific gravity greater than water. Densiron (one of the two available heavy silicone oil's) is a mixture of perfluorohexyloctane (F6H8, with a specific gravity of 1.35 g/ml and viscosity of 2.5 mPas), and conventional silicone oil (specific gravity of 0.97 g/ml and viscosity of 5700 mPas depending on the molecular weight). The specific gravity of Densiron is 1.06 g/ml and the viscosity is 1400 mPas, making it a novel heavier-than-water, long-term internal tamponade agent, which means that in the upright position it sinks and provides support for the inferior retina.