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Femtosecond laser corneal ablation threshold: dependence on tissue depth and laser pulse width
Hui Sun1, Meng Han, Markolf H Niemz
1Department of Ophthalmology, University of California, Irvine, California 92697, USA.
Background And Objective:
Diode pumped, all-solid-state ultrafast lasers are now widely used to perform minimally invasive refractive surgery and keratoplasty procedures. Despite such use, a systematic study concerning ultrafast laser-tissue interactions is lacking. We determined the corneal ablation threshold as a function of the laser pulse width and stromal depth by simultaneous monitoring of the intensity of the laser-induced plasma and the second harmonic generation signals (SHG) from the collagen.
Study Design/Materials And Methods:
Ablation thresholds in porcine cornea samples were determined using three diode pumped all-solid-state ultrafast lasers (a Nd:glass femtosecond laser, a Yb:KYW femtosecond laser, and a Nd: YAG picosecond laser) over a range from 800 femtoseconds to 20 picoseconds.
Results:
Corneal ablation threshold remained nearly constant within the first 200 microm of stroma and was consistent with previous findings with the threshold proportional to the square root of the laser pulse width.
Conclusion:
Corneal ablation thresholds can be precisely determined by simultaneous monitoring of the intensity of the laser-induced plasma and the SHG from the cornea.
