Influence of emulsification on silicone oil additive effects on rabbit corneal endothelial permeability

Previous studies have shown that emulsification of a pure silicone oil had little influence on rabbit corneal endothelial permeability to inulin or dextran. Several compounds, known to be present in some impure silicone oils, increase corneal endothelial permeability measured in vitro after presentation to the endothelium in vivo for 1 week. Because emulsification vastly increases the surface area to volume relationship of an oil and offers a shorter diffusion distance to the oil surface/aqueous humor interface, there is a greater opportunity for loss of oil constituents into the local environment. Experiments were performed, therefore, to determine whether emulsification of oils containing specific additives gave a greater permeability increase than when the additive was included in nonemulsified oil. The results indicate that emulsification does not necessarily enhance the capacity of every additive to increase corneal endothelial permeability although this can occur. It is apparent that sufficient quantities of certain additives can diffuse out of a large, single oil bubble in the anterior chamber sufficient to increase endothelial permeability, but the increase in surface area caused by emulsification does not always result in an increased corneal endothelial permeability. The differences may reflect different absorptive properties of the oil or the much reduced diffusion distance to the surface of the oil droplet to different additives (e.g., binding constants, release kinetics).