Influence of pulsed laser irradiation on the morphology and function of the guinea pig cochlea

Recent experimental and clinical studies have demonstrated that several pul sed laser systems are also suitable for stapedotomy. The aim of the study w as to investigate morphological and functional inner ear changes after irra diating the basal turn of the guinea pig cochlea with two pulsed laser syst ems of different wavelengths. The Er:YSGG (lambda = 2.78 mu m) and Ho:YAG ( lambda = 2.1 mu m) lasers were used applying the laser energies necessary f or perforating a human stapes footplate. The cochleas were removed 90 min, 1 day 2 weeks, or 4 weeks after laser application. Acoustic evoked potentia ls (compound action potentials) were measured before and after laser applic ation and at the above times immediately before removal of the cochleas. Th e organ of Corti was examined by scanning electron microscopy. Application of Er:YSGG laser parameters effective for stapedotomy had no adverse effect s on Corti's organ in the guinea pig cochlea. On the other hand, effective Ho:YAG laser parameters cause damage to the outer hair cells with fusion of . stereocilia and formation of giant cilia leading to partial or total cell loss. The inner hair cells and supporting cells were usually normal. These morphological data show a good correlation with the electrophysiological m easurements. Our results clearly demonstrate that, besides achieving effici ent bone management, the Er:YSGG laser has high application safety. On the other hand, the Ho:YAG laser is not well tolerated in our animal study. Its use in stapedotomy would be unreliable and dangerous for the inner ear. (C ) 2000 Elsevier Science B.V. All rights reserved.