Videographic and histologic comparison of Nd:YAG and diode laser contact transscleral cyclophotocoagulation

We performed contact transscleral cyclophotocoagulation in two human autopsy eyes with continuous-wave Nd:YAG and diode lasers. Duration of exposure was two seconds, and powers were 4 to 7.3 W with the Nd:YAG laser and 1.75 to 2.5 W with the diode laser. In both procedures, we used hand-held quartz fiberoptic contact probes for energy delivery. Tissue responses were viewed with high-magnification videographic recording technique to analyze the real-time laser effects. The treated tissues were then studied by light microscopy. We observed different tissue responses both videographically and histologically. Nd:YAG laser lesions were characterized by prominent tissue whitening and contraction of the ciliary epithelium, while the diode laser lesions had less whitening and the tissue contraction appeared to be deeper in the ciliary body. The histologic correlate was coagulation and disruption of the ciliary epithelium and little effect on the underlying ciliary muscle with the Nd:YAG laser, while the diode laser had less effect on the ciliary epithelium but caused a significant coagulative response in the ciliary muscle. Comparative trials are needed to establish the clinical significance of these videographic and histologic observations.