Study of stromal femtosecond laser ablation for deep corneal cut optimization
Résumé
Femtosecond laser has become a common tool in corneal surgery during the last years. The first clinical application of femtosecond lasers (FL) in ophthalmology was in refractive surgery (LASIK : laser in situ keratomileusis) for the preparation of cornea flaps [1]. Recently, FL applications have been extend to penetrating and lamellar keratoplasty. However, commercially available femtosecond laser in ophthalmology have already shown limitations in these new applications, in particular in oedematous cornea (pathologic or stored by eye banks). Experimental and clinical investigations of deep lamellar and penetrating graft in oedematous corneas have often shown bad quality dissections, with the presence of numerous remaining tissue bridges [2, 3]. In order to improve the results of these dissections, a fine knowledge of the dissected biological material is essential. The human cornea is a complex tissue made of different layers. The stroma, central layer mainly made of collagen fibrils and water, represent more than 90% of the whole corneal thickness. Collagen fibrils organization and hydration in the stroma is not homogeneous too. Anterior stroma owns a complex collagen fiber branching patterns, which decreased logarithmically in posterior direction [4].The purpose of this study is to investigate interactions between FL and human corneal stroma. The study has been realised on human corneal grafts unsuitable for transplantation. Corneal grafts have been prepared with a mechanical corneal microkeratome. A lamellar cut from anterior side has been performed in at two different depths: 50µm for anterior stroma study and 350µm for posterior stroma study (see figure 1-c). This preparation is intended to prevent any interference between the incident laser and the other corneal layers. Ablation thresholds and ablation rates have been studied on remaining anterior and posterior corneal stroma for different processing configuration, such as laser fluence and pulse number. Results of this study will show if the inhomogeneous histological organization of the corneal stroma and pulse number have implications on ablation thresholds and rates. If this is the case, these results could be used to improve FL ablation parameters for deep cornea cut.