Diode laser contact transscleral cyclophotocoagulation: getting the most from the G-probe

To determine the multi-use behavior of the G-probe that is traditionally marketed as a single-use cyclophotocoagulation instrument.

A diode laser equipped with a G-probe was used to perform cyclophotocoagulation of the ciliary body in 4 human cadaver eyes and 15 porcine eyes (1,750 mW x 2 seconds). A determination of G-probe effectiveness was made following measurements of G-probe energy output, scanning electron microscopy examination of probe tips, and histologic examination of treated tissue.

The mean energy output of 12 of the 15 G-probes remained constant at 3.10 J (range, 3.04 to 3.14 J) for 20 treatment cycles of 20 applications each. Scanning electron microscopy demonstrated minimal surface change. Three G-probes suffered a significant drop-off in energy output during the experiment, and scanning electron microscopy showed significant surface change. Histologic examination of human eyes treated with laser revealed disruption of the ciliary body stroma and separation of pigmented and nonpigmented layers of the ciliary epithelium. More pronounced tissue necrosis and disruption was observed in eyes treated with newer G-probes. Milder coagulative damage with cellular vacuolization was observed in G-probes used for higher numbers of treatment cycles.

Every G-probe tested delivered more than 100 consecutive applications of laser energy before any loss of efficiency was noted. This suggests that in the absence of obvious structural damage, a G-probe may be safely used for treatment of at least 5 eyes.