[Trabeculoplasty with two different lasers in cats, monkeys and humans: a scanning electron microscopy study].

PURPOSE To study the structural changes induced by trabeculoplasty with two different lasers (Ti-Sph and argon) and observe the differences between four trabecular meshwork models. MATERIALS AND METHODS Four different trabecular meshwork (TM) models were used from cats, monkeys, and humans. This study was performed on fresh cadaver eyes ("ex vivo") except for the cat in which this study was performed "in vivo". The morphology of the trabecular meshwork was observed by scanning electron microscope (40/100X) after being treated with argon (0.1s/pulse, 600 to 1,000 mW, 50 microm spot size) and Ti-Sph (7 microsg/pulse, 25 to 110 mJ,175 microm of spot size). The study on cats allowed assessment of the induced effect after 24 hours, and 4 weeks after the treatment on the TM. Typical clinical trabeculoplasty parameters were used for both lasers during this study. RESULTS The models used in this study were found to be adequate for trabeculoplasty. They exhibited a deep anterior chamber and an accessible TM. The argon laser induced significant changes in the TM in all models studied. The cat model demonstrated TM repair response one month after treatment. For Ti-Sph, high levels of energy (>100 mJ) were required to induce significant structural changes in the TM. CONCLUSION The IOP reduction effect by argon trabeculoplasty (600/1,000 mW) induced structural shrinkage of the collagen in the TM via thermal effects. The Ti-Sph laser works through non-structural mechanisms. At clinical levels (lower than 80 mJ), Ti-Sph does not show evidence of TM changes.