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Caractérisation objective et quantitative de la transparence cornéenne par OCT plein champ et microscopie holographique

Abstract : Lack of corneal transparency is a major cause of blindness worldwide, affecting over 10 million people. Early diagnosis and quantitative follow-up could improve clinical outcome and hence prevent blindness. There is thus a critical need for reliable and easy-to-use clinical tools for objective and quantitative characterisation, including monitoring ability, of corneal transparency.In collaboration with Rémi Carminati (Institut Langevin, ESPCI, CNRS), we have developped a physical model of light scattering in the cornea, including as few parameters as possible, able to describe scattering properties of the cornea. We have also analysed the nanostructure of the collagen fibrills (main components of the corneal stroma, whose organisation is mandatory for transparency) from transmission electron microscopy images, modeling the interaction potential between fibrils with only one parameter.In addition to this theoretical analysis we have studied scattered light in transmission using digital holographic microscopy (DHM) and in reflection using full filed optical coherent tomography (FF-OCT). Transmission geometry enables us to observe the effects of light scattering on the retina and therefore to the visual acuity. Reflection geometry is the one used in clinical practice and therefore the one from which the scattering properties of the cornea have to be determined. For the analysis of the OCT signal, we have developed, in collaboration with Pascal Pernot (University of Paris Sud, CNRS), a Bayesian analysis that allows us to extract the scattering mean free path and its possible fluctuations in depth. We first used this analysis on ex vivo FF-OCT images of healthy corneas from the eye-bank, and pathological corneas collected after corneal transplant surgery. We have thus shown that this analysis makes it possible to measure the scattering mean free path with great precision and also to determine if a cornea presents heterogeneities. Finally, we have demonstrated the feasibility of this in vivo analysis by applying it to clinical OCT and slit lamp images, and we have obtained very good reproducibility of our measurements as well as a correlation between the measurements made by the two imaging methods.
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Romain Bocheux. Caractérisation objective et quantitative de la transparence cornéenne par OCT plein champ et microscopie holographique. Optique [physics.optics]. Université Paris Saclay (COmUE), 2019. Français. ⟨NNT : 2019SACLY009⟩. ⟨tel-02928883⟩

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