We evaluated the efficacy, safety, and stability of femtosecond laser intrastromal refractive procedures in ex vivo and in vivo models. When compared with longer pulsewidth nanosecond or picosecond laser pulses, femtosecond laser-tissue interactions are characterized by significantly smaller and more deterministic photodisruptive energy thresholds, as well as reduced shock waves and smaller cavitation bubbles. We utilized a highly reliable, all-solid-state femtosecond laser system for all studies to demonstrate clinical practicality. Contiguous tissue effects were achieved by scanning a 5 μm focused laser spot below the corneal surface at pulse energies of approximately 2 - 4 microjoules. A variety of scanning patterns was used to perform three prototype procedures in animal eyes; corneal flap cutting, keratomileusis, and intrastromal vision correction. Superior dissection and surface quality results were obtained for lamellar procedures (corneal flap cutting and keratomileusis). Preliminary in vivo evaluation of intrastromal vision correction in a rabbit model revealed consistent and stable pachymetry changes, without significant inflammation or loss of corneal transparency. We conclude that femtosecond laser technology may be able to perform a variety of corneal refractive procedures with high precision, offering advantages over current mechanical and laser devices and techniques.
We investigated three potential femtosecond laser ophthalmic procedures: intrastromal refractive surgery, transcleral photodisruptive glaucoma surgery and photodisruptive ultrasonic lens surgery. A highly reliable, all-solid-state system was used to investigate tissue effects and demonstrate clinical practicality. Compared with longer duration pulses, femtosecond laser-tissue interactions are characterized by smaller and more deterministic photodisruptive energy thresholds, smaller shock wave and cavitation bubble sizes. Scanning a 5 (mu) spot below the target tissue surface produced contiguous tissue effects. Various scanning patterns were used to evaluate the efficacy, safety, and stability of three intrastromal refractive procedures in animal eyes: corneal flap cutting, keratomileusis, and intrastromal vision correction (IVC). Superior dissection and surface quality results were obtained for the lamellar procedures. IVC in rabbits revealed consistent, stable pachymetric changes, without significant inflammation or corneal transparency degradation. Transcleral photodisruption was evaluated as a noninvasive method for creating partial thickness scleral channels to reduce elevated intraocular pressure associated with glaucoma. Photodisruption at the internal scleral surface was demonstrated by focusing through tissue in vitro without collateral damage. Femtosecond photodisruptions nucleated ultrasonically driven cavitation to demonstrate non-invasive destruction of in vitro lens tissue. We conclude that femtosecond lasers may enable practical novel ophthalmic procedures, offering advantages over current techniques.
We characterized the effects of pulse duration, pulse energy, and spot separation on intrastromal corneal photodisruption to determine parameters that achieve optimal surface quality and tissue plane separation. Experiments utilized two laser systems, a 60 picosecond Nd:YLF laser and a 450 femtosecond Nd:Glass laser, both operating at 1.06 micrometers wavelength. Photodisruption was performed by tightly focusing the laser beam 150 microns below the tissue surface and scanning it in a spiral pattern to create a plane. A cut to the surface was made with the laser and the two surfaces separated to form a flap. Tissue plane separation was graded according to the additional mechanical dissection required. Internal surfaces were analyzed with standard histologic methods and scanning electron microscopy. We found that the Nd:YLF laser required approximately three times the pulse energy to achieve intrastromal cuts. Picosecond parameters also required more mechanical dissection and produced lower surface quality than optimal femtosecond parameters. We conclude that femtosecond laser pulses offer significant advantages that make them ideal candidate tools for high precision intrastromal corneal surgery. The flexibility in laser pulse delivery opens up a number of potential surgical applications not possible with current mechanical or laser devices.