Morphological Effects of Laser Irradiation on the Cochlea

Abstract

Argon laser irradiation was applied to the stria vascularis of the third turn through the otic capsule of guinea pigs and to the osseous spiral lamina and the organ of Corti through the round window membrane. A laser probe, 0.6 mm in diameter, was connected to an argon laser. A glass fiber of 200μm in diameter was encased in the probe. Each time, the power applied was 50-300 mW and of 0.5-second duration. The tip of the probe was 0.5 to 1 mm away from the otic capsule. Twenty-six to 48 days after irradiation, the animals were killed under deep anesthesia after intravital fixation with Heidenhein-Susa solution. The conventional celloidin-embedding technique was used to make sections of 20μm thickness for microscopic observation. The spiral ligament showed atrophy and the stria vascularis disappeared in the third turn. The otic capsule remained intact. The organ of Corti was partly or completely missing. Extension of Reissner's membrane covered the atrophic spiral ligament and was connected to the basilar membrane after the spiral ligament had disappeared. Irradiation (1W×0.5 seconds) through the round window membrane destroyed the organ of Corti and fractured the bony shelf of the osseous spiral lamina with loss of dendrites of cochlear neurons. The round window membrane remained intact.