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 Ultrashort Lasers in Refractive Surgery
In the project “Femtosecond LASIK” studies referring to the application of ultrashort laser pulses in the field of refractive surgery are conducted.
Therefore, laser pulses with pulse duration of several hundred femtoseconds ( 1fs = 10-15 s ) are focused into the anterior part of the eye, the so-called cornea. Due to nonlinear absorption processes based on the very high field intensities of the fs-pulses, the originally transparent cornea becomes ionised and cuts inside the bulk of the material can be created. This cutting effect is achieved by multiphoton absorption and cascade ionisation and termed as optical breakdown.
To achieve an excellent cutting precision and low collateral damage in the tissue, the underlying processes have to be well understood and the laser parameters optimised.
Thus, several effects, like thermal damage, cavitation, pressure wave generation have to be studied. Because of the nonlinear character of the fs-application, effects like generation of higher harmonics, self-focusing, self-phase modulation, become important and have to be taken into account.
In refractive surgery, the fs-laser can be used to overcome several problems of the standard procedure, the so-called Laser in situ Keratomileusis (LASIK). During this procedure, a cut has to be created by a mechanical guided knife within the treated eye, allowing the opening of the cornea and, subsequently, an ablation of tissue by an excimer laser inside the eye. This mechanical cut probably leads to undesired complications, due to incomplete cutting or woundhealing reactions etc.
Because of its nonlinear nature, the fs-laser is, in contrast to the excimer laser, able to work inside the treated eye, without the need of an opening of the patients eye, making the mechanical cut obsolete.
In preliminary studies, conducted in cooperation with the Institute of Pathology at the School of Vetenary Medicine Hannover, performed at ex-vivo (dead) pig-eyes and in-vivo (living) rabbit eyes, promising results were found and the very low side effects and
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