Assessing bulk emulsification at the silicone oil - saline solution interface in a 3D model of the eye

Emulsification of silicone oil (SiOil) in a vitrectomized eye was investigated using a 3D model of the vitreous cavity to test the hypothesis that oil droplet formation arises from the breakdown of the bulk SiOil-aqueous interface during eye saccadic movement.

Round bottom flasks filled with SiOil and a saline phase modelled the vitrectomized SiOil-filled eye. A stepper motor imposed saccadic movements and the oil/aqueous interface was monitored with digital cameras. A range of SiOil viscosities, flask diameters, motion scenarios and levels of fill were studied. Estimates of velocity profiles in the fluid on the equatorial plane of a sphere subject to saccadic motion were obtained from an analytical solution to the Navier-Stokes equations.

Interfacial waves were observed at saccadic motions with higher acceleration, amplitude and frequency. Low interfacial tension between the two fluids, lower oil viscosity and smaller level of SiOil fill all promoted large deformations of the interface. No droplets were formed at the bulk SiOil-aqueous interface. However, formation and detachment of oil droplets were observed at the three-phase contact line under certain conditions.

The stresses generated at the liquid-liquid interface are not large enough to form droplets in the bulk region for conditions representative of these in the eye. Bulk emulsification of the SiOil, reported as the main formation mechanism by some workers, is not responsible for droplet formation in a vitrectomized SiOil-filled eye set-up. This result confirms recent finding on droplet formation driven by a surface emulsification mechanism.