Argon laser irradiation to the semicircular canal

In order to elucidate the effects of argon laser irradiation on the lateral semicircular canal of the guinea pig, the vestibular labyrinth was histologically studied after irradiation, using the conventional celloidin method. Irrigation of the external meatus with ice water was used to evaluate the function of the semicircular canal by recording caloric nystagmus. When irradiation was performed, a laser probe was approximated to the lateral canal, 0.5 to 1 mm away from the surface of the 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, and subjected to celloidin processing. The irradiated bony wall of the lateral canal demonstrated charring. Lucent areas were observed around and under the charred area. The semicircular duct showed shrinkage with disappearance of the trabecular mesh. New bone formation was observed along the endosteum of the irradiated area. The lateral canal was completely occluded by ossification with or without fibrosis when sufficient energy was applied. The anterior and posterior canals were normal. Caloric tests using 5 mL of ice water for 5 s failed to elicit nystagmus on the irradiated side.