Surgery of the anterior segment of the eye assisted by ultrashort pulse laser: optimisation of the parameters with respect to tissular transparency and cell viability

Abstract : The goal of this work was to study different microscopic and macroscopic effects that will ultimately help us to improve procedures in eye surgery assisted by ultrashort pulse lasers and most notably keratoplasty (corneal grafting), which requires laser systems which are operational in pathological and therefore strongly light scattering tissue. Previously, the Optique Photonique Santé (OPS) group at the Laboratoire d'Optique Appliquée (LOA) had identified 1650 nm as an optimum wavelength at which light scattering processes inside the pathological cornea are minimised. During the present thesis, three main tasks have been addressed. An ultrashort pulse laser system based on non-linear optical crystals has been developed, optimised with respect to the requirements of laser eye surgery, and fully char-acterised. The finished set-up is compact, robust, simple and potentially qualified for clinical use. In collaboration with a group at IESL-FORTH (Iraklion, Greece) and with the participation of a previous PhD student of the group we have studied the interaction of ultrashort pulses with water, collagen (type I) solution and porcine cornea. Data on laser-tissue-interaction is precious because the interaction dynamics is usually only documented for water; our results will help to develop a tissue-specific model for the interaction process. We have investigated the interaction of the laser pulses and the effects it causes with live cells in the corneal endothelium. The preservation of endothelial cell viability is crucial notably for specific keratoplasty routines which require incisions close to the endothelium; compromised endothelial cell viability – which is likely caused by the effects of shock waves generated by optical breakdown and bubble formation – may lead to a failure of the surgical intervention. “Safe” sets of parameters concerning pulse energy and incision geometry need to be defined. We explored the maximum permitted pulse energy values at any given distance to the endothelial cells and mini-mal distances for given pulse energies and estimated the associated shock wave amplitudes.
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Syed Asad Hussain. Surgery of the anterior segment of the eye assisted by ultrashort pulse laser: optimisation of the parameters with respect to tissular transparency and cell viability. Physics [physics]. École Polytechnique, 2014. English. ⟨tel-01097301⟩

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