Effects of pulsed Er : YSGG and Ho : YAC laser on the organ of corti of the guinea pig cochlea - a scanning electron microscopic study.

Background: Recent experimental studies have demonstrated that, apart from the continuous wave lasers, several pulsed laser systems are also suitable for stapedotomy. The aim of this study was to clarify whether irradiation o f the basal convolution of the guinea pig cochlea could cause morphological inner-ear changes using the Er:YSGG and Ho:YAG laser with laser parameters required for stapedotomy. Methods: After opening the bulla, the basal conv olution of the guinea pig cochlea, whose thickness is similar to that of th e human stapes footplate, was irradiated with the Er:YSGG and Ho:YAG laser. The laser parameters used were those necessary for an adequate perforation of a human stapes footplate (500-600 mu m). The cochleae were removed 90 m inutes, 1 day, 2 weeks, or 4 weeks after laser application. The organ of Co rti was examined by scanning electron microscopy in all convolutions. Resul ts: Application of Er:YSGG laser parameters effective for stapedotomy (5 pu lses, energy: 85 J/pulse, energy density: 36 J/cm(2), total energy: 0.425 J ) had no adverse effects on the organ of Corti in the guinea pig cochlea. O n the other hand, effective Ho:YAG laser parameters (10 pulses, energy: 210 J/ pulse, energy density: 90 J/cm(2), total energy: 2.1 J) caused damage t o the outer hair cells with fusion of stereocilia and formation of giant ci lia leading to partial or total cell loss. The inner hair cells and support ing cells were usually normal. Conclusion: Our results clearly demonstrate that the Er:YSGG laser has high application safety. It could prove to be a viable alternative to the thermically acting CO2 laser for stapedotomy. The Ho:YAG laser is not well tolerated in animals and has low application safe ty. Its use in stapedotomy would be unreliable and dangerous for the inner ear.