Role of blood components in ocular silicone oil emulsification: Studies on an in vitro model

Purpose. To develop an in vitro model for silicone oil emulsification and to explore the blood components involved in this process. Methods. The capacity of various blood components to support silicone oil (1000 CS) emulsification was studied by applying 0.5 ml oil on top of 0.5 ml saline containing various blood components. Each tube was sonicated for 150 seconds and centrifugated at 5000g for 20 minutes. Three phases were noted in the tube: At the top was clear silicone oil, in the middle was emulsified silicone oil, and at the bottom was aqueous solution. The tubes were photographed, and the percentage of the phase length containing emulsified silicone oil (middle) of the total length of the three phases was calculated from the projected image of each tube. Results. Emulsified silicone oil in plasma or serum was initiated after 100 seconds of sonication and quickly reached maximum (approximately 80%) at 120 seconds. The size of these oil droplets prepared in vitro was 0.0467 ± 0.028 mm, closely resembling that observed in oil samples removed from a patient's anterior chamber (0.038 ± 0.018 mm). Under these conditions, silicone oil emulsified in the presence of whole blood cells occurred only at a concentration of 120 μg protein/ml; in the presence of red blood cell membranes, it occurred at a concentration of 60 μg protein/ml. Lipoprotein-deficient serum failed to support emulsification; however, samples of high-density lipoprotein and low- density lipoprotein supported this process. Purified high-density lipoprotein-apolipoprotein supported oil emulsification. The addition of phosphatidylcholine further enhanced this process, but phosphatidylcholine alone failed to support emulsification. Conclusions. A simple and fast in vitro model to study factors affecting silicone oil emulsification was developed. Using this model, red blood cell membranes, plasma lipoproteins, and purified HDL-apolipoproteins supported silicone oil emulsification. LIpids did not, but they had the capacity to enhance the apolipoprotein- supported emulsification.