A femtosecond laser, normally used for LASIK eye surgery, is used to perforate cadaveric human stapes. The thermal side effects of bone ablation are measured with a thermocouple in an inner ear model and are found to be within acceptable limits for inner ear surgery. Stress and acoustic events, recorded with piezoelectric film and a microphone, respectively, are found to be negligible. Optical microscopy, scanning electron microscopy, and optical coherence tomography are used to confirm the precision of the ablation craters and lack of damage to the surrounding tissue. Ablation is compared to that from an Er:YAG laser, the current laser of choice for stapedotomy, and is found to be superior. Ultra-short-pulsed lasers offer a precise and efficient ablation of the stapes, with minimal thermal and negligible mechanical and acoustic damage. They are, therefore, ideal for stapedotomy operations.
The Er:YAG laser has been shown to be a effective and safe tool for middle ear surgery, due to its wavelength of
2.94 μm matching a peak in the absorption spectrum of tissue. The development of a compact laser provides similar
optical properties with the additional advantage of being a smaller and more flexible system. The laser-tissue interaction
of the laser with porcine otic capsule bone, including photoacoustic effects and ablation characteristics are presented here
and compared to those of an Er:YAG laser, to show its suitable for middle ear surgery. Photoacoustic effects were
recorded using a piezo-electric film. Ablation rates were determined by mass loss per pulse and etch depth per pulse.
A laser has been developed with the aim of being a microsurgical tool for ear surgery. Its emission at 2.7 - 2.8 μm is
readily absorbed by water in tissue. This makes it ideal for ablation of the stapes, while minimizing transmission to the
inner ear. Slices of porcine otic capsule bone to represent the stapes were ablated with the laser. The mechanical stress
imparted to the stapes during ablation was measured using a piezoelectric film. The Er:YAG laser has similar optical
properties, but this laser offers the possibility of a more compact surgical tool.
One of the main problems during laser stimulation in human pain research is the risk of tissue damage caused by excessive heating of the skin. This risk has been reduced by using a laser beam with a flattop (or superGaussian) intensity profile, instead of the conventional Gaussian beam. A finite difference approximation to the heat conduction equation has been applied to model the temperature distribution in skin as a result of irradiation by flattop and Gaussian profile CO2 laser beams. The model predicts that a 15 mm diameter, 15 W, 100 ms CO2 laser pulse with an order 6 superGaussian profile produces a maximum temperature 6 oC less than a Gaussian beam with the same energy density. A superGaussian profile was created by passing a Gaussian beam through a pair of zinc selenide aspheric lenses which refract the more intense central region of the beam towards the less intense periphery. The profiles of the lenses were determined by geometrical optics. In human pain trials the superGaussian beam required more power than the Gaussian beam to reach sensory and pain thresholds.