Peer-Reviewed Literature:

The use of a laser in place of a mechanical keratome for flap creation was a turning point in the field of refractive surgery. Visible and near infrared laser light are absorbed by the refractive structures of the eye and allowed to pass freely into the eye without effect at low-power densities. At high-power densities, the nonlinear optical properties of the cornea lead to absorption, generating plasma. The infrared neodynium-glass femtosecond laser emits a wavelength similar to that of an Nd:YAG laser, which is used widely in ophthalmic surgery. Each femtosecond laser pulse is approximately 10,000 times shorter in duration compared with a Q-switched Nd:YAG laser and lasts only about 10 to 13 seconds. Unlike photothermal lasers, the peak intensities of the femtosecond laser create plasma inside transparent tissues such as the cornea, without interfering with surface tissue. Femtosecond laser pulses require significantly less energy to produce photodisruption compared with longer pulse-width lasers, such as picosecond and nanosecond. This lower energy threshold translates into smaller cavitation bubbles and allows the nearly contiguous placement of laser pulses. The femtosecond laser has been used for making flaps, creating intrastromal tunnels for intrastromal corneal ring segments, keratomileusis with lenticule removal, and intrastromal PRK in which corneal tissue is withdrawn without disturbing the epithelium.