STAPEDOTOMY USING CONTINUOUS WAVE DIODE LASER (808 NM)

Abstract

To the Editor: We read with interest the recent article of Gerard et al. (1), which attempted to shed light on the prognostic factors in stapes surgery. The authors indicated that they found a significant loss in bone conduction threshold immediately postoperatively in all but one frequency. They also indicated that the drop in the bone conduction threshold at 4,000 Hz did not completely recover after 2 to 6 months. In reviewing the authors' surgical technique, they stated that they used a diode laser (wavelength, 808 nm) in continuous mode at 1 W for "fragilization" of the stapes footplate. We think that the selection of wavelength and power may have contributed to the change in the bone conduction thresholds that the authors report. The 808-nm diode laser emits light in the near-infrared range (not in the visible spectrum as stated in the article), which is poorly absorbed by the otic capsule bone of the stapedial footplate unless an initiator, such as blood, is used. Also, there is significant evidence that using a continuous-wave (CW) mode laser can lead to a much higher temperature of the target bone than pulsed mode (2). The authors did not specify the irradiation time, but at this wavelength, anything above 100 ms likely exceeds the thermal relaxation time of this tissue at 808 nm (3). In addition, poorly absorbed wavelengths such as that produced by the 808 nm diode laser, specifically, has been associated with diffuse heating when used on a continuous mode in nonabsorbent tissue (4). Combined with long laser exposure times, volumetric heating and heat conduction may play significant roles as the conditions for thermal confinement are nowhere remotely satisfied (5). We think that the diode (808 nm) laser without an initiator is not well suited for a stapedectomy, given its poor absorption in bone. The use of CW laser irradiation is especially not prudent on the footplate, given the significant heat that is generated. The heat produced by this laser in CW mode may be the cause of the drop in bone conduction threshold observed by the authors. Acknowledgments: This study was performed at the University of California Irvine Medical Center. The authors thank Brian J. F. Wong, M.D., Ph.D., for expertise and consultation. Hamid R. Djalilian M.D. Alice D. Lee M.D. Division of Otology, Neurotology, and Skull Base Surgery Department of Otolaryngology-Head and Neck Surgery University of California Irvine Irvine, California, U.S.A.