Reference : UMR7649-JEAALL-001
Workplace : PALAISEAU
Date of publication : Tuesday, May 10, 2022
Scientific Responsible name : Jean-Marc ALLAIN
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
The cornea is a tissue with unique optical properties, thanks to its transparency and curvature. These properties are closely linked to its mechanical behaviour, which shows a viscoelastic response. This behaviour is supposed to preserve the curvature of the cornea whatever the stresses (variations of intraocular pressure, shocks...).
It is accepted that the mechanical properties of the cornea are related to its micrometric organisation and more particularly to that of its main component, the stroma. The stroma is a connective tissue, made up of lamellae a few micrometres thick, themselves made up of collagen fibrils aligned and regularly spaced. It is this highly structured organisation that allows the transparency of the cornea, by preventing the diffusion of light. The lamellae are organised in a plywood-like structure, with more or less interpenetration depending on the depth in the stroma.
The objective of the thesis is to build, from experimental observations, a model linking the microstructure to the mechanical properties in the cornea to improve laser surgery procedures of the cornea.
Indeed, laser surgery treatments of the cornea are becoming more and more frequent with the increase of myopia in the population. However, the outcome of these treatments will depend on the patient, due to varying healing capabilities and different mechanical properties. If the mechanical properties of the cornea are too altered by surgery, a complication may arise, with the development of keratoconus which is associated with a local decrease in corneal stiffness.
This project will be carried out in close collaboration between the LMS and the LOB of the Ecole Polytechnique (Pr. Schanne-Klein's team) and the Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts in Paris (Pr. Vincent Borderie's team).
The first step will be to characterize the mechanical properties of the cornea in relation to the microstructure.
To do this, we will carry out swelling tests on corneas, using different observation methods (optical tomograph - OCT, second harmonic generation microscope - SHG, confocal, etc.) to be able to observe the different constituents (collagen, cells, etc.) of the cornea and their evolution during a mechanical test. Particular attention will be paid to the measurement of local deformation in volume (via the monitoring of cells or natural markers). In addition, we will be interested in the evolution of Voigt's striae, which are folds of the lamellae in the cornea and whose role is not understood, as well as in the role of fluid exchanges between the cornea and its environment (osmotic or poromechanical effects). We will first characterize healthy corneas and then pathological or treated corneas.
In addition, a model of the cornea will be developed. This model will be based on existing models (including the one already initiated in the laboratory), which will be modified and completed to include Voigt striations and fluid exchange effects. The model will be identified via our experimental data; Finally, we will look at the sensitivity of its response to its parameters, distinguishing between parameters that can be measured in the clinic and those that cannot be patient-specific. The ultimate goal is to reproduce surgical operations and their consequences via this model.
The thesis will be carried out at the Laboratoire de Mécanique des Solides, a joint unit between the CNRS and the Ecole Polytechnique. The LMS is interested in the mechanics of materials and structures, with in particular themes linking mechanics and other disciplines (physics, biology, etc.). More specifically, the thesis will be carried out in the M3DISIM team, which is interested in the problems of mechanics for biology and medicine.
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