Traction on the retina in the presence of posterior vitreous detachment. Abstract

Transcription

1 Traction on the retina in the presence of posterior vitreous detachment Abstract

2 Posterior vitreous detachment (PVD) The vitreous progressively shrinks and detaches from the retina in the posterior part of the vitreous chamber (syneresis) PVD is a patho physiological condition very common in elderly vitreous cortex At point of strong adhesion between the vitreous cortex and the retina the detached vitreous may exert a traction on the retina and possibly induce the generation of retinal tear static traction: due vitreous shrinking dynamic traction: due to oscillations of the gel liquefied vitreous interface

3 Posterior vitreous detachment liquefied vitreous retinal break gel

4 Rhegmatogenous retinal detachment A retinal tear may evolve to a retinal detachment, i.e. the separation of the retina from its underlying supportive tissue. The liquefied vitreous enters through the retinal break and progressively causes detachment The physical mechanisms governing this process are yet unclear The retina cannot function when these layers are detached, and unless it is reattached soon, permanent vision loss may result.

5 Formulation of the problem Working assumptions 2D model: the vitreous cavity is a circle At least at the linear level the dynamics of the system is expected to be similar to the 3D case It is much easier and faster to perform a sensitivity analysis of the results on the parameters At the interface between the gel and the liquefied vitreous we have a one dimensional elastic membrane Vitreous gel: incompressible Mooney Rivlin solid (non linear elastic response) with a dissipation term Liquefied vitreous: Newtonian fluid Vitreous cortex: elastic membrane Fully numerical approach Comsol Multiphysics (FEM) large amplitude eye rotations (saccades) large amplitude oscillations of the interface

6 Mechanical properties of the vitreous Lee et al., Biorheology, 1992 The authors describe the vitreous with a 4 parameter viscoelastic model We just consider: an elastic constant a viscosity coefficient elatsic properties of the membrane?

7 Examples of saccadic movements angular displacement angular velocity

8 Duration amplitude relationship Empirical relationships exist expressing saccade duration and maximum angular velocity as a function of the rotation amplitude

9 Reproduction of real saccadic movements angular position angular velocity maximum angular acceleration: (dω /dt)max = deg/s2, maximum angular velocity Ω max= ~ 600 deg/s maximum angular velocity and saccade duration depend on saccade amplitude

10 Time variation of the force at the inferior attachment point of the membrane A=2 F [N/m] T [s]

11 Time variation of the force at the inferior attachment point of the membrane A=10 F [N/m] T [s]

12 Time variation of the force at the inferior attachment point of the membrane A=15 F [N/m] T [s]

13 Time variation of the force at the inferior attachment point of the membrane A=20 F [N/m] T [s]

14 Dependence of the maximum traction on the retina on the amplitude of the saccade

15 Dependence of the maximum traction on the retina on the elastic properties of the membrane ratio between the membrane and solid elastic constants

16 Work in progress Investigation on the dependence of the traction on the retina on the shape of the gel liquid interface different values of the ratio volume of solid/ volume of fluid attachment angle of the membrane on the retina are there types of PVD more likely to produce a retinal tear? Different types of movement Is it feasible to expect resonance phenomena Eigenfrequencies of the system Comprehensive sensitivity analysis of the results on the controlling parameters Three dimensional simulations