Skip to Main content Skip to Navigation
Theses

Greffe de cornée automatisée assistée par laser femtoseconde optimisé en longueur d'onde

Abstract : My PhD project was conducted within the framework of the “GRECO” project (ANR-06-TecSan-025) which is coordinated by our group and funded by the French National Research Agency. Following the success of femtosecond laser technology in refractive surgery, the project aims to extend the application of these lasers to corneal grafting. Most of the indications for corneal grafting are associated to an insufficient optical quality of the patient's cornea, which also compromises the intervention by laser. Our findings suggest that the strong optical scattering of the pathological corneas at the laser wavelengths presently used can be compensated by an increase of the wavelength of lasers towards the window of relative tissular transparency centred at 1,65 µm. Our project partners are the Hôtel-Dieu hospital at Paris, the Imagine Eyes company and the Institut d'Optique Graduate School. Objectives of the thesis The principal objectives of my thesis were the following: - The development of laser sources optimised for corneal grafting based on nonlinear wavelength conversion; - The study of the laser-tissue interaction process in view of optimising the laser parameters; - The conception and realisation of a demonstrator device for laser surgery. Results Laser source based on Optical Parametric Amplification The work plan of the GRECO project comprised the assembly of a flexible and parametric laser source based on a laser titanium:sapphire pump source in order to perform laboratory experiments covering a broad wavelength range. We chose an architecture based on the OPA principle which consists of two amplification stages (based on two crystals of different characteristics) preceded by the injection of a supercontinuum. The first stage provides good wavelength selectivity and the second a strong gain, particularly at twice the pump wavelength. The conversion efficiencies on the system are of about 20 % over the entire wavelength range of accordability. The system supplies pulses of 300 µJ tuneable between 1.2 µm and 1.75 µm for the signal. This source served for all the exploratory surgical experiments of the first half of the GRECO project. Laser source based on Optical Parametric Generation (OPG) In parallel to the surgical experiments on the laser-tissue interaction, I developed a second source taking into account the requirements for clinical use. This second source is pumped by a compact and stable commercial solid state laser emitting at 1.03 µm. This wavelength is converted by optical parametric generation in a single nonlinear periodically poled crystal without injection; the system remains thus simple, compact and stable. The wavelength tuneability of the amplified signal is obtained by a change in the temperature of the crystal. Thus, no realignment is needed, which contributes to the robustness of the system. A single passage provides a conversion efficiency of about 20 % and maximum pulse energy of 20 µJ, which corresponds to a performance a 100 times greater than the state of art. The use of several periodically poled structures in the same crystal leads to an overall tuneability of the signal between 1450 nm and 1900 nm and thus covers the entire spectral range of corneal transparency and opacity in the short wavelength infrared. Surgical results on the cornea and on the sclera Our surgical experiments have been performed on corneas obtained under permission from the French Eye Bank. We have conducted a systematic study of the penetration depth and the quality of the surgical result as a function of wavelength and the pathological state of the cornea. In parallel, systematic measurements of the corneal transparency depending on the presence and degree of oedema have been made. The transparency measurements and the surgical experiments using the OPA or OPG have shown a strong dependence of the penetration depth on wavelength. - The use of wavelengths around 1 µm corresponding to present clinical systems is compromised by a very limited penetration depth in oedematous cornea. This conclusion agrees with the experience of our medical partners who estimate that the performances of clinical systems are limited when used for corneal grafting. - Using longer wavelengths limits the contribution of light scattering. However, the absorption band of water centred at 1.45 µm increases the contribution of thermal effects; the use of wavelengths close to this band therefore is not possible - A window of relative transparency centred at 1.65 µm exists, within which absorption is weak and the contribution of light scattering is almost negligible. We have observed an overall improvement of a factor of about 3 compared to lasers working at wavelengths around 1 µm. The quality of the incisions is excellent and the validity of the work hypothesis of the GRECO project has thus been demonstrated. The demonstrator device for an automated corneal graft with complex geometries The work plan of the GRECO project also comprised the assembly of a demonstrator device, combining the elements for an optimised system permitting corneal grafting. The demonstrator consists of three modules. The first unit contains the laser is alternatively the aforementioned OPG device or a compact fibre laser emitting at 1.6 µm developed at the Institut d'Optique Graduate School. The second unit contains a module of adaptive optics. The third unit allows the delivery of the beam to the cornea and its positioning in three dimensions. The system is controlled by a computer interface based on LabView software. Conclusion and perspectives During my thesis work I have developed two innovative and powerful nonlinear laser sources respectively based on the principle of optical parametric amplification and generation. The performances notably of the second system are largely superior to the state of art and have permitted us to anticipate a milestone of another project funded by the National Agency of Research. The source corresponds to the criteria of reliability and compactness necessary for a clinical device. This source is at the basis of ongoing discussions of a technology transfer project. These sources have permitted to identify and to demonstrate the advantages of corneal surgery at 1.65 µm. We have mounted a demonstrator system based on this wavelength which incorporates a wavefront correction module and a beam delivery system. The OPS group is now in a position to extend its activities in femtosecond laser surgery to other applications as glaucoma surgery in the sclera and new projects in cataract surgery or gene transfection.
Document type :
Theses
Complete list of metadatas

Cited literature [66 references]  Display  Hide  Download

https://pastel.archives-ouvertes.fr/pastel-00577221
Contributor : Florent Deloison <>
Submitted on : Wednesday, March 16, 2011 - 5:47:15 PM
Last modification on : Wednesday, July 3, 2019 - 10:48:02 AM
Long-term archiving on: : Friday, June 17, 2011 - 2:45:37 AM

Identifiers

  • HAL Id : pastel-00577221, version 1

Collections

Citation

Florent Deloison. Greffe de cornée automatisée assistée par laser femtoseconde optimisé en longueur d'onde. Optique [physics.optics]. Ecole Polytechnique X, 2010. Français. ⟨NNT : 2501924230J⟩. ⟨pastel-00577221⟩

Share

Metrics

Record views

1420

Files downloads

1648