Lasers for Otosclerosis

Abstract

The concept of using laser energy to perform stapedotomy and stapedectomy revision is an attractive one. Precision of vaporizing a perfectly round 0.6- to 0.8-mm hole in the stapes footplate, regardless of its thickness or degree of fixation, would introduce an elegant simplicity to a sometimes difficult operation while eliminating mechanical trauma to the inner ear. When revising a previously failed stapedectomy, lasers should enable the otologic surgeon to atraumatically vaporize the obliterating oval window tissue and thus precisely diagnose the cause of the failure. A laser stapedotomy could then be performed in the membranous oval window, thus minimizing the risk of recurrent prosthesis migration. To accomplish these objectives, lasers must possess physical properties which permit the precise controlled delivery of laser energy to the microscopic operative field. Tissue characteristics of this laser energy should permit the vaporization of the stapes footplate or oval window soft tissue without thermal effect to the vestibule and without passing through the perilymph to damage the delicate structures of the inner ear. Two types of lasers have been successfully used for otosclerosis surgery: the visible lasers (Argon and KTP-532) and the invisible CO2 laser. This paper explores relative merits and disadvantages of each. The visible lasers possess ideal optical properties for microsurgery and, until recently (1984), were the only group of lasers optically precise enough for safe use on the oval window. Unfortunately, the short wavelength of these visible lasers (0.5 mu) impart tissue properties which are less than ideal for otosclerosis surgery. Visible laser is only partially absorbed by the white stapes footplate and readily passes through the perilymph to be absorbed by pigmented tissue of the inner ear (blood vessels, neuroepithelium, etc.). Therefore, the Argon and KTP-532 lasers should be used with caution while performing stapedotomies. Visible lasers should not be used for stapedectomy revisions since direct application of visible laser energy to the open vestibule produces dramatic temperature rises (up to 175 degrees C) in the vestibule at the level of the utricle and saccule. The long wavelength of the invisible CO2 laser (10.6 mu) imparts many optical problems which limit its precision for microscopic surgery. Until recently, the CO2 laser was too inaccurate for otosclerosis engineering advances for CO2 microsurgery. A newly designed microslad optical delivery system could deliver a 0.3-mm spot size CO2 beam at 250-mm focal length which was satisfactorily par-focal and coaxial with the aiming HeNe beam.(ABSTRACT TRUNCATED AT 400 WORDS)