DEGRADATION-INDUCED TRANSMISSION LOSSES IN SILICA OPTICAL FIBERS

Background and Objective: The interaction of surgical optical fibers w ith tissue has been studied. Study Design/Methods and Materials: Fiber s (600 mu m) were lased in chicken and beef tissue using a Nd:YAG lase r from 5 to 50 W in both cw and pulsed modes.Results: With longer lasi ng and higher power, larger transmission loss and degradation (burn-in ) of the fiber tip, occurred. This degradation converts the Nd:YAG las er power to heat and leads to further energy loss. During contact lasi ng, tissue and blood adhere to the fiber tip surface limiting laser tr ansmission, desiccating, and eventually destroying adhering tissues. S uch tissue residues create high power densities and temperatures at th e tip, which then cause a variety of degradation processes to be initi ated. Conclusion: ''Burned-in'' fibers do not photocoagulate; rather t hey incise tissue. With continued lasing, thermal shock, chemical, and mechanical breakdown of the fiber leads to failure of the fiber tip a nd the spalling of glass fragments into the tissue bed. (C) 1997 Wiley -Liss, Inc.