The effect of serum proteins on dynamic interfacial properties of silicone oils in vitrectomized eyes

The planning of refractive surgical interventions is a challenging task. Numerical modelling has been proposed as a solution to support surgical intervention and predict visual acuity. We propose a numerical framework to simulate patient-specific intervention based on corneal topography acquired on the patient. A validation study performed on patients who underwent cataract surgery showed that the model was able to predict the level of astigmatism induced by the intervention. We can conclude that the numerical simulation can become a valuable tool to plan corneal incisions in cataract surgery and other ophthalmo-surgical procedures in order to optimize patients’ refractive outcome and visual function.


Towards a full model for ocular biomechanics, fluid dynamics and hemodynamics
measured with atomic force microscopy (AFM).
The elastic modulus of the tissue was reduced in all enzyme treated samples relative to controls.In addition, collagen fibril organisation was disrupted by proteoglycan depletion.Our data demonstrate that proteoglycans play an important role in determining not only the mechanical properties at these length scales but also collagen fibril arrangement.
Polarimetric interferometry to objectively evaluate the optical properties of corneal stroma  Abstract -The formation and stability of emulsions in vitrectomized eyes is linked to the properties of the silicone oilaqueous humor interface, in particular the surface tension.In the presence of natural surfactants, such as serum and plasma, the value of the surface tension is likely to change, but little quantitative information is presently available.To this end we perform accurate experiments measuring the interfacial properties of silicone oil (Siluron 1000) with an aqueous solution in the presence of endogenous-like proteins.It is found that the surface tension is significantly reduced when physiologically realistic concentrations are used.Moreover, the obtained values of the dilational viscoelastic modulus are compatible with the formation of stable emulsions.

Mathematical modelling of ocular and cerebral hemo-fluid dynamics:
Application to VIIP  ITA 2017)  28-29 September 2017, Rome -Italy   ISBN: 978-88-6296-000-7 Email: prudhomme@unistra.fr;szopos@math.unistra.fr6 Department of Electrical Engineering & Computer Science, University of Missouri, Columbia, MO, USA Email: guidobonig@missouri.edu Abstract -This work aims at investigating the interactions between the flow of fluids in the brain and eyes and their potential implications in the development of visual impairment and intracranial pressure (VIIP) syndrome in astronauts.We propose a reduced (0-dimensional) mathematical model of fluid circulation in eyes and brain, which is embedded into a simplified whole-body circulation model.This model allows us to predict fluid redistribution in the upper body vasculature and variation of the intracranial (ICP) and intraocular (IOP) pressures.The model results suggest that, by taking into account some effects of microgravity, it is possible to observe IOP increase, blood flow decrease in the choroid and ciliary body circulation.These findings provide clues on the role that vascular components may play in VIIP pathogenesis, for which astronauts could be screened on earth and in-flight.
Keywords: visual impairment and intracranial pressure syndrome; intracranial pressure; intraocular pressure; blood flow.Abstract -The dynamic tonometer test (air puff test) is an invivo investigative procedure routinely utilized in ophthalmology to estimate the intraocular pressure (IOP).A rapid localized air jet applied on the anterior surface induces the inward motion of the cornea, which interacts with the aqueous humour -filling the narrow space between cornea and iris -with a strong influence on the dynamics of the cornea.Potentially the test, quick and painless, could be combined with inverse analysis methods to characterize the patient-specific mechanical properties of the human cornea.As a step towards this aim, the present study describes a fluidstructure interaction (FSI) approach based on a simplified geometry to simulate the anterior chamber of the eye undergoing the air puff test.We regard the cornea as a nonlinear elastic and isotropic membrane described through an analytical model and discretize the weakly compressible Newtonian fluid with a meshfree particle approach.Numerical analyses reveal a marked influence of the fluid on the dynamics of the cornea.Additionally, we investigate the possibility to use the dynamics of the test to estimate the intraocular pressure.

A meshfree approach to cornea-aqueous humor interaction during tonometry tests
Keywords: meshfree methods; particle methods; collocation methods; fluid-solid interaction; fluiddynamics; air puff test.
Fluid-structure interaction of the non-contact tonometry test Abstract -We propose a mathematical model of fluid transport across the retinal pigment epithelium (RPE), aimed at understanding the mechanisms that govern the flow.Quantitative description of this flow is relevant, as fluid accumulation in the subretinal space is related to several pathological conditions such as, in particular, age related macular degeneration (AMD).Possible mechanisms that drive water flow across the RPE are osmosis and electro-osmosis.We develop a model, which couples electrophysiology and fluid dynamics in the RPE.The model predicts the existence of ion concentration gradients in the cleft gap between adjacent cells and these gradients drive an osmotic flux, which is comparable with the measured water flux across the We also find that local osmosis is the dominant mechanism for water transport and electro-osmotic flow is subdominant, and this result is robust with change of parameters.Abstract -In this paper we formulate a poroelastic model starting from a model of species diffusion in an elastic material.The governing equations are derived from general thermomechanical principles.We carefully revise the role of the energy-stress Eshelby tensor, mutuated from the framework of tissue growth, in describing the hemo-mechanical behaviour of the tissue.The model accounts for nonlinear deformations of the solid matrix and deformation induced changes in porosity and permeability.The model is applied to study the mechanics of the lamina cribrosa in the eye.This is a porous tissue at the head of the optic nerve.Deformation of this tissue and impairment of blood flow induced by tissue deformation are considered to be related to the pathogenesis of glaucoma.

Saccadic movement effects on intraocular drug delivery for a wet-AMD clinical case
M. Ferroni 1 , M. Cereda 2 , F. Boschetti 1 1 Dept.Chemistry, Materials & Chemical Engr."G.Natta", Politecnico di Milano, Italy  Email: {marco.ferroni,federica.boschetti}@polimi.it  2 Dept.Biomedical & Clinical Sci.Luigi Sacco, Sacco  Hospital, University of Milan, Italy  Email: matteo.cereda@gmail.comAbstract -Nowadays, intravitreal injections are the gold standard for the treatment of age-related macular degeneration (AMD).The prediction of the transport mechanism for the injected anti vascular endothelial growth factor (anti-VEGF) is needed in order to understand its distribution and consumption after each injection.Thus, this study aims at implementing a full model of the vitreous drug delivery.The main novelty of this work is the coupling between an experimental evaluation of the scleral permeability and a numerical analysis of the saccadic dependency of the transport phenomena.