Mechanical Models of the Dynamics of Vitreous Substitutes

In the present paper we discuss some aspects of the fluid dynamics of vitreous substitutes in the vitreous chamber, focussing on the flow induced by rotations of the eye bulb. We use simple, yet not trivial, theoretical models to highlight mechanical concepts which are of great relevance to understand the behaviour of vitreous substitutes in the vitreous chamber and also to identify ideal properties for vitreous replacement fluids. We first consider the dependency of the maximum shear stress on the retina on the viscosity of the fluid, and also discuss the differences between the motion of purely viscous and viscoelastic fluids. We then investigate how the wall shear stress changes if a thin layer of aqueous is present in the vitreous chamber, separating the retina from the vitreous replacement fluid. In relation to this, we also discuss results from a theoretical model that predicts the stability conditions of the interface between aqueous and a vitreous substitute. We discuss the implications of this model results to understand the mechanisms leading to the formation of an emulsion in the vitreous chamber.