Hypothesis: Making a cochleostomy with a laser can affect the inner ear function.
Background: Different types of lasers can be used to create a fenestration in the footplate of the stapes during stapedotomy. Because of variations in absorption spectra of the laser light in various tissues or fluids, each laser has its own characteristics and possible side effects.
Materials and methods: The basal turns of the cochleae of 20 guinea pigs were fenestrated using 4 types of lasers (thulium, KTP, CO2, diode; all groups n = 4). A control group (n = 4) was included to correct for the effects of the surgery alone. At 3 different time points, acoustically evoked compound action potentials (CAPs) were recorded at 5 frequencies and at different sound pressure levels. N1-P2 amplitudes were measured, and subsequently, thresholds were calculated. A repeated measures analysis of variance was used to investigate differences between groups.
Results: There was a decrease in CAP amplitudes and an increase in CAP thresholds after cochleostomy with each laser. The increase in thresholds was significantly larger for higher frequencies. The thulium laser evoked the largest threshold shifts, the KTP laser the smallest with the CO2, and diode lasers in intermediate positions. Overall, there was an increase in latencies after treatment.
Conclusion: Laser treatment on or near the cochlea can cause damage to the sensitivity of the cochlea for sound. The thulium laser seems to be the worst choice in this respect.