Optimized underwater diathermy for vitreous surgery

The properties of radio frequency (RF) diathermy currents are briefly reviewed. The inadequacy of damped currents is stressed. The recommended machine generates a frequency of 13.56 MHz. It has a power amplifier, crystal control, coaxial lead from machine to handle, and an impedance of 200 ohms. The two types of electrodes and handles described are shielded from the electrode tip to the diathermy machine. One has a short handle, and an electrode angulated at 35degrees, used in open-sky vitrectomies. The other has a longer handle and straight probe, and is provided with a system for saline infusion. It is used in closed transscleral operations. Electrodes require 35 to 50% more current when used underwater than when used on dry sclera. If charring of tissue is to be avoided, it is advisable to keep the intensity near the level at which gas bubbles form at the electrode tip. Blood vessels can be closed reliably and safely with these electrodes.