TEMPERATURE AND PRESSURE EFFECTS DURING ERBIUM LASER STAPEDOTOMY

Background and Objectives: Laser-assisted stapedotomy has become a wel l-established alternative to the mechanical drilling method. The goal of this study is to quantify the mechanical and thermal tissue effects and to determine optimum erbium laser parameters for safe clinical tr eatment. Study Design/Materials and Methods: On an inner ear model, ti me-resolved pressure measurements and Schlieren optical flash photogra phy were performed during the perforation of the stapes foot plate usi ng an erbium laser at 2.79 mu m. The laser radiation was transmitted v ia an optical zirconium fluoride fiber. The laser-treated foot plates were investigated by light microscopy and scanning electron microscopy to visualise the laser-induced tissue effects. Results: Perforation o f the stapes foot plate can be performed with a few erbium laser pulse s with high precision and a thermal damage zone of <10 mu m. Strong pr essure transients were found to be generated by the bone ablation proc ess and the collapse of a vapor channel created in the perilymph after fenestration. Conclusion: From the comparison of the laser-induced pr essure with the limit graph to avoid hearing defects published by Pfan der, an unobjectionable use of the erbium laser is deduced for fluence s <10 J/cm(2). The erbium laser seems to represent an ideal instrument for middle ear surgery with all the advantages (precision, fiber opti c transportable, high ablation efficiency, safety) desired for clinica l application. (C) 1996 Wiley-Liss, Inc.