Mechanical Models of the Dynamics of Vitreous Substitutes

Abstract

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 that are relevant to understand the dynamics of vitreous substitutes and also to identify ideal properties for vitreous replacement fluids. We first recall results by previous authors, showing that the maximum shear stress on the retina grows with increasing viscosity of the fluid up to a saturation value. We then investigate how the wall shear stress changes if a thin layer of aqueous humour is present in the vitreous chamber, separating the retina from the vitreous replacement fluid. The theoretical predictions show that the existence of a thin layer of aqueous is sufficient to substantially decrease the shear stress on the retina. We finally discuss a theoretical model that predicts the stability conditions of the interface between the aqueous and a vitreous substitute. We discuss the implications of this model to understand the mechanisms leading to the formation of emulsion in the vitreous chamber, showing that instability of the interface is possible in a range of parameters relevant for the human eye.

Flow dynamics of vitreous humour during saccadic eye movements

“…Those results were later corroborated by Isakova et al [21], who predicted the same trend using an analytical approach, and also by Bonfiglio et al [22] who also obtained similar results based on an experimental study. Modarreszadeh and Abouali [23] focused on providing a reliable numerical procedure for the study of VH as a viscoelastic substance and under oscillatory movements.…”

Macro- and Microscale Properties of the Vitreous Humor to Inform Substitute Design and Intravitreal Biotransport

“…Finally, there has been increased interest in the biotransport of the vitreous humor and vitreous substitutes, particularly due to increased clinical use of intravitreal injection to deliver therapeutics. 10,16,18,[168][169][170][171][172][173][174][175][176][177][178][179][180][181][182][183] The motion of fluid inside the vitreous (intact or liquefied) due to eye rotation or saccadic eye movement has been investigated by many groups, 168,169,171,180,183 with particular implications shown for drug delivery and pharmacokinetics in the vitreous. 170,172,173,178,184 A model of enzymatic degradation of the vitreous was created and used to study the mobility of intravitreal nanoparticles, which could better simulate the biotransport of a therapeutic injected into aged and liquefied vitreous.…”

“…18 An in vitro ocular flow model called the PK-Eye was proposed for use in preclinical drug development, 175 which can allow for testing of therapeutics in vitreous substitutes. 174,181,182 These advances will enable significant progress in determining pharmacokinetics and therapeutic feasibility at earlier stages. However, these advancements are still mostly based on the in vitro properties of the vitreous humor, which likely limits their usefulness and accuracy in in vivo applications.…”

DNA Supramolecular Hydrogel as a Biocompatible Artificial Vitreous Substitute

“…[ 21 ] Furthermore, strain‐dependent rheological test demonstrated a linear viscoelastic regime up to strains exceeding 10% (Figure S1, Supporting Information), which is higher than the highest strains experienced in the vitreous cavity. [ 22 ] This means that the DNA hydrogel could tolerate the dynamic environment of vitreous cavity and is likely to maintain its solid‐like properties in the vitreous cavity. These results can be explained by the rigidity of the DNA components, which is also consistent with previous reported phenomena.…”