Combined use of perfluorohexyloctane and silicone oil as intraocular tamponade: an in vitro study.

Background: Double filling (DF) with perfluorohexyloctane (F6H8) and silicone oil (SIL) has been recently proposed and tested clinically as a means to improve the tamponade properties of single components. This in vitro study investigated (1) the kinetics of the mixing process of F6H8 with SIL (1,000 mPa s) and (2) the contact and emulsification behaviour of DF as compared with pure liquids, with the aim of assessing the tamponade efficiency and its evolution with time. Methods: (1) The velocity of the mixing process for F6H8+SIL was estimated by monitoring the position of the interphase in a rectangular cell kept at constant temperature. (2) The surface contact and the tendency to emulsification of DF and of SIL and F6H8 were visually examined by using a Perspex eye model. Results: (1) The mixing process for F6H8+SIL is slow. In the absence of stirring, equilibrium is reached no earlier than 1 month at 37 degrees C. (2) F6H8 was found to show close contact with the eye model and dispersion into droplets; SIL showed poor contact with the cell surface and no dispersion; DF exhibited poor contact with the superior cell surface and little evidence of dispersion. Conclusions: F6H8 dissolves slowly in SIL and equilibrium is only reached after 1 month. The final ratio of the DF phases differs from the initial ratio. An initial F6H8/SIL ratio of 70%:30% vol results in 25% vol of pure F6H8 (density, 1.33 g/cm(3)) and 75% vol of a solution containing F6H8, viz. 60% vol F6H8 in SIL (density 1.17 g/cm(3)). Because of its density and contact properties, the investigated DF has a tamponade effectiveness better than that of SIL on the inferior retina. Compared with using F6H8 alone, DF reduces emulsification.