Comparison of temperature measurements and fundus reflectometry in laser coagulation.

In light coagulation, thermal Parameters play an important role for the biological reaction. Therefore, we measured the temperature increase and the whitening of the coagulation site simultaneously during the coagulation. Microthermocouples [I] were developed as shown in figure 1. The diameter of the tip ranges between 5 and 10 pm, the response time of this element is in the region of 1 msec. We designed a technique to insert this thermocouple into the globe through a trepanation at the Pars plana (fig. 2). The tip is advanced by a step motor and can be positioned exactly by a micromanipulater anywhere within the posterior pole. Coagulation of 500 ,um in diameter were set in rabbit eyes with an argon laser coagulator using a slitlamp contact lens arrangement. The temperature in the center of the lesion at the interface between the PE and retina is monitored during and after the coagulation (fig. 3). To demonstrate our method, figure 4 shows a typical temperature course duiing a weak coagulation. The light reflected from the coagulation site is monitored simultaneously with the temperature. The details of this technique have been reported in a paper at the 1976 Gonin Meeting in Lausanne by Bivngrubev et al. [2]. The upper curve of figure 4 shows the temperature course as a function of time, the lower curve shows the corresponding course of the reflccted light. In this case, the temperature increases by about 35 "L, but no change of the reflected light can be observed. This indicates that the