ARGON-LASER IRRADIATION TO THE SEMICIRCULAR CANAL

In order to elucidate the effects of argon laser irradiation on the la teral semicircular canal of the guinea pig, the vestibular labyrinth w as histologically studied after irradiation, using the conventional ce lloidin method. Irrigation of the external meatus with ice water was u sed to evaluate the function of the semicircular canal by recording ca loric nystagmus. When irradiation was performed, a laser probe was app roximated to the lateral canal, 0.5 to 1 mm away from the surface of t he canal. Each time, power applied was 1.0 W on the dial of the laser machine. The duration of irradiation was 0.5 s. The lateral canal was irradiated one to 15 times. Twenty-five to 87 days after irradiation, the temporal bones were fixed in Heidenhein-Susa solution, removed, an d subjected to celloidin processing. The irradiated bony wall of the l ateral canal demonstrated charring. Lucent areas were observed around and under the charred area. The semicircular duct showed shrinkage wit h disappearance of the trabecular mesh. New bone formation was observe d along the endosteum of the irradiated area. The lateral canal was co mpletely occluded by ossification with or without fibrosis when suffic ient energy was applied. The anterior and posterior canals were normal . Caloric tests using 5 mL of ice water for 5 s failed to elicit nysta gmus on the irradiated side.