Optic Fibers for Laser Therapeutic Endoscopy

Abstract

The recent proliferation of laser use in medicine was the direct result of advances in the technology of laser light transmission. The first methods of laser light transmission used direct transmission or articulated mirrors. However, these systems are bulky and are now used only for CO₂ lasers. The reasons are 1) optic fibers transmitting the 10.6 um wavelength of CO₂ are still under development, and 2) optic fiber transmission would not allow the sharply focused point necessary for surgical incision. The development of optic fibers in the seventies facilitated the adaptation of lasers to endoscopy. The principle of transmission is based upon total internal reflection. The waveguide is made up of two components, an inner core which transmits the light and an outer cladding which continuously reflects the light internally. The first work in the development of laser light transmission by fiber-optics was carried out between 1973 and 1975 by two groups in Germany. Fruhmorgen, Boden et al (1) for argon laser and Nath, Kiefhaber et al. (2) for Nd:YAG laser. Boden et al. (1) used a plastic fiber with a polymethyl methacrylate core (i.e. plexiglass). However, power loss through the fiber was a major problem, and this particular fiber produced a 50% loss per meter of fiber length. Also, the divergence angle at the fiber tip was over 12 degrees making its application clinically quite difficult. Nath, et al. (2) developed the ‘Triconic fiber’ which is still used clinically by Kiefhaber. This fiber allows the transmission of Argon and Nd:YAG light with little power loss (less than 20% for 4 meters) and a narrow beam divergence (2 to 4 degrees). But this fiber is very fragile; it has to be fixed in a specially modified endoscope. Protection from contamination is made by a quartz window screwed in the tip of the endoscope.