Ultrastructural and Histologic Studies of Femtosecond Laser Incisions in Human Cornea

Abstract : Purpose: The authors present ultrastructural and histologic studies of femtosecond laser incisions in human cornea. Methods: We use a CPA femtosecond laser designed to match current instrumentation for femtosecond surgery, i.e. a Nd:Glass femtosecond laser at a 1065 nm wavelength. The repetition rate is adjustable from 1 to 10 KHz, with maximum pulse energy of 60 µJ. The human cornea samples are fixed to an anterior chamber system that can be moved in 3D by micrometric precision motors in front of a fixed objective delivering the fs laser pulses. Human corneas are provided by the French Eye Bank. Laser energy range for cornea treatment goes from laser induced optical breakdown threshold up to ten time this threshold. Ultrastructural and histologic are then obtained using transmission electronic microscopy TEM and scanning electron microscopy (SEM). Results: Observations of the cornea structures (i.e. epithelium, Bowman membrane, stroma, Descemet membrane and endothelium) presents no noticeable side damages like burned collagen or cells damage. Results does not vary with pulse energy (in the experimental energy range : 2 J/cm2 to 50 J/cm2) except for excessive delamination due to the shock wave propagation at high energy. Conclusions: The use of femtosecond laser pulses for keratoplasty implies use of energy higher than the one used for refractive surgery in transparent cornea. Our results demonstrate that cornea ultrastructure is not altered by this higher energy pulses opening the way to surgery in oedematous cornea.