Plasma formation and shielding by three ophthalmic neodymium-YAG lasers.

Because microplasma formation may provide an energy-absorbing shield that protects the retina from inadvertent injury during neodymium-YAG laser surgery, we studied plasma formation and shielding by three ophthalmic neodymium-YAG lasers (the Q-switched American Medical Optics YAG-100, the mode-locked Meditec OPL-3, and the Q-switched LASAG Sirius Microruptor 2) with three model targets (physiologic saline, 1% sodium hyaluronate, and a cellophane membrane). Plasma formation produced a linear reduction in the transmission of light energy along the beam path in a qualitatively differences. Plasma shielding was similar in both saline and sodium hyaluronate; enhancement of the shield effect occurred only with the cellophane membrane target. Operating the lasers at energy levels far above threshold did not reduce total light transmission significantly. Clinical use should be guided by the principle of employing the minimum energy necessary to cut the target tissue.