Towards better characterization and quantification of emulsification of silicone oil in vitro

Emulsification is related to complications arising from silicone oil (SO) tamponade. Currently, there is no widely accepted method for testing the propensity of SO to emulsify that are physiologically realistic and quantitative.

We compared different ways of inducing emulsification namely vortex mixing, sonication and homogenization. Silicone oil (SO) emulsification was quantitatively assessed using the Coulter counter and laser light scattering. The in vitro results are compared with the droplet size distribution profile of vitreous clinical washout. Conventional SO was compared with two novel SO blends with high-molecular-weight (HMW) additives (SO_HMW2000 and SO_HMW5000 ).

Of the three methods for inducing emulsification, homogenization generated the most consistent emulsion samples with the smallest variance. The results from the Coulter counter measurement correlated strongly with the laser light scattering measurement within the range of 1 to 30 µm. The droplet size distribution profiles from human eyes were similar to that of emulsions generated in vitro by homogenization. The human size distribution profile was within the range of values obtained by the in vitro experiment. Compared to the conventional SO, the emulsion droplet counts for the new SO blends were significantly lower (SO_HMW2000 and SO_HMW5000 were 79% (±17%) and 49% (±18%) of the SO₂₀₀₀ and SO₅₀₀₀ , respectively; p = 0.03 and p = 0.002).

Emulsion generated in vitro by homogenization has similar droplet size profile as human eyes filled with SO. Using this method to induce emulsion, SO blends with HMW additives demonstrated less propensity to emulsification with lower droplet counts compared to conventional SO with similar shear viscosity.