Ablation dynamics in laser sclerotomy ab externo

Ralf Brinkmann; Gerit Droege; Dirk Mohrenstecher; M. Scheu; Reginald Birngruber

doi:10.1117/12.229582

10 January 1996 Ablation dynamics in laser sclerotomy ab externo

Ralf Brinkmann, Gerit Droege, Dirk Mohrenstecher, M. Scheu, Reginald Birngruber

Proceedings Volume 2632, Lasers in Ophthalmology III; (1996) https://doi.org/10.1117/12.229582
Event: BiOS Europe '95, 1995, Barcelona, Spain

Abstract

Laser sclerostomy ab externo with flashlamp excited mid-IR laser systems emitting in the 2-3 micrometer spectral range is in phase II clinical trials. Although acutely high success rates were achieved, the restenosis rate after several months is about 40%. Laser pulses of several hundreds of microseconds, known to induce thermo-mechanical explosive evaporation were used for this procedure. We investigated the ablation dynamics in tissue and the cavitation bubble dynamics in water by means of an Er:YAG laser system to estimate the extent of mechanical damage zones in the sclera and in the anterior chamber, which may contribute to the clinical failure. We found substantial mechanical tissue deformation during the ablation process caused by the cavitation effects. Stress waves up to several bar generated by explosive evaporization were measured. The fast mechanical stretching and collapsing of the scleral tissue induced by cavitation resulted in tissue dissection as could be proved by flash photography and histology. The observed high restenosis might be a result of a subsequent enhanced wound healing process. Early fistula occlusions due to iris adherences, observed in about 20% of the clinical cases may be attributed to intraocular trauma induced by vapor bubble expansion through the anterior chamber after scleral perforation. An automatic feedback system minimizing adverse effects by steering and terminating the laser process during scleral fistulization is demonstrated. Moreover, a new approach in laser sclerostomy ab externo is presented using a cw-IR laser diode system emitting at the 1.94 micrometer mid-IR water absorption peak. This system was used in vitro and showed smaller damage zones compared to the pulsed laser radiation.

Citation Download Citation

Ralf Brinkmann, Gerit Droege, Dirk Mohrenstecher, M. Scheu, and Reginald Birngruber "Ablation dynamics in laser sclerotomy ab externo", Proc. SPIE 2632, Lasers in Ophthalmology III, (10 January 1996); https://doi.org/10.1117/12.229582

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