Rapid development of new laser technologies enabled the application of ultra short lasers in refractive surgery. Focused ultra short laser pulses in near-infrared spectral range can generate a laser induced breakdown (LIB) in the cornea, which will disrupt the tissue. Cutting depth and position can be established by varying the laser focus. The fs-LASIK technique allows both flap and lenticule to be formed by using fs-pulses without the presence of any mechanical impact. During the cutting process not all of the pulse energy is deposited into the cornea; approximately half of the remaining energy propagates through the eye and reaches the retina. Though defocused, the transmitted energy can still induce damage to the retina due to absorption by the retinal pigment epithelium and the transfer of thermal energy to surrounding tissue. The fs-LASIK process was simulated with two laser systems; one continous-wave and one in the fs-regime. For the simulation the exposure time and focusing numerical aperature which defines the retinal spot size were varied. The Damage thresholds of the laser beam exposed eyes were determined in terms of ophthalmoscopic and histopathologic observations.
Ultrashort laser pulses are increasingly used in refractive eye
surgery to cut inside transparent corneal tissue. This is
exploited by the fs-LASIK procedure which affords the opportunity
to correct ametropia without any mechanical effects. The cutting
process is caused by the optical breakdown occurring in the laser
focus. During this process only a certain amount of the pulse
energy is deposited into the tissue. The remaining pulse energy
propagates further through the eye and interacts with the retina
and the strong absorbing tissue layers behind. Therefore this
investigation shall clarify if the intensity of the remaining
laser pulse and the resulting temperature field can damage the
retina and the surrounding tissue. Threshold values of the retinal
tissue and theoretical calculations of the temperature field will
be presented.
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