Mechanisms of femtosecond laser-cornea interaction in keratoplasty

The objective of the present research work has been to study the femtosecond laser-tissue interaction in order to define optimal conditions for performing keratoplasty of pathological corneas by femtosecond laser. This is the first thesis on the subject accomplished at the Laboratoire d’Optique Appliquée (Ecole Polytechnique, ENSTA, CNRS in Palaiseau) and it has been carried out in close collaboration with the Laboratoire Biotechnologie et Œil (Université Paris Descartes, EA 4063, Hospital Hôtel Dieu de Paris). The femtosecond laser is currently used in refractive surgery for cutting tissue and recently it has been introduced for substituting traditional mechanical instruments for corneal transplant or keratoplasty, which consists in replacing a pathological cornea of a patient with a healthy cornea from a donor. Approximately 100 000 procedures are performed per year worldwide. Leading indications for keratoplasty involve opacification of corneal tissue due to a dysfunction of the endothelial cells. The cornea becomes permeable and looses its transparency. The oedema degree increases progressively and, if not interrupted by transplantation, it can cause total opacification of the cornea and a drastic decrease of the visual acuity. Traditional techniques for keratoplasty present a high risk of rejection, insufficient visual recovery and/or a risk of failure because technically delicate. In this context, femtosecond lasers represent a safe, accurate, and reliable surgical tool. However, clinical systems commercially available are very successful in cutting transparent corneal tissue (donor) but present technical limitations when inducing dissection in pathological corneas (receiver). At the interface between the physics and the ophthalmology, this research work has allowed to assess the potential and the limitations of the present clinical systems and it has brought solutions for optimizing the laser-tissue interaction, also indicating directions for the development of a further high performing system. This research work received the "Fondation Dalloz Institut de France" Prize 2007 and the "La Recherche" Prize 2008.