[New approach for determining the damage level of biological tissues using femtosecond laser: advantages and application to corneal surgery].
BACKGROUND
Optimization of femtosecond laser characteristics in corneal surgery is still needed to improve clinical results. In this study, we describe an original characterization technique able to measure laser damage of corneal tissues precisely and to provide complementary physical results on the laser-matter interaction.


METHODS
A femtosecond laser was used to damage corneas not suitable for graft. The epithelium and the Bowman layer are exposed to a set of different single-shot fixed laser fluences. Optical microscopy can determine the probability of laser damage on the corneal surface. The high damage threshold (minimum fluence systematically damaging the cornea) roughly fixes the operating laser fluence conditions, while the low damage threshold sets the maximum laser fluence level preserving tissue integrity (safety level).


RESULTS
We precisely evaluate the damage fluence threshold of a tissue, using a statistical approach coupled with optical microscopy analysis. This technique gives essential information on laser-tissue interaction with a high rate of confidence. For corneal epithelium and the Bowman layer, we determine the maximum laser fluence level preserving tissue integrity (safety level) and the minimum fluence level systematically damaging the tissue. High and low threshold fluences of epithelium and the Bowman layers are (5.6 ± 0.4 J/cm(2); 2.7 ± 0.1 J/cm(2)), and (7.1 ± 1.1 J/cm(2); 3.4 ± 0.1 J/cm(2)), respectively.


CONCLUSIONS
These data constitute determinant parameters for clinical applications, since they determine a working window providing the minimal effective irradiation dose that is mandatory for the development of high-quality laser-cutting surgery processes with minimized side effects.
Département d'ophtalmologie, hôpital de la Timone, université de la Méditerranée, 264, rue Saint-Pierre, 13385 Marseille cedex 05, France. Louis.hoffart@ap-hm.fr
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Conrath
D003315:Cornea / Q000601:surgery*; D065306:Corneal Injuries; D053685:Laser Therapy / Q000009:adverse effects* / Q000379:methods; D008954:Models, Biological; D013508:Ophthalmologic Surgical Procedures / Q000379:methods