Quantitative CW Nd:YAG pars plana transscleral photocoagulation in postmortem eyes.

The effect of different types of burns and numbers of lesions on, and the role of initial pressure head in, the rate of aqueous outflow was studied in enucleated human and porcine eyes. Noncontact and contact CW Nd:YAG laser applied to human eyes 3 mm posterior to the limbus produced a 34% and 51% increase, respectively, in outflow as compared with controls (P = .01). In porcine eyes, outflow increased directly with the number of noncontact burns as well as with the amount of perfusion pressure. Our results suggest that intraocular pressure and outflow are functions of both the intensity of irradiation and the surface area treated, and that each individual pressure head may require an optimal pars plana area of treatment of therapeutic degree to lower pressure and yet prevent overfiltration and phthisis. Our results also suggest that there may be a passive transneuroepithelial and transscleral outflow component in clinical laser cycloablation and, therefore, a need to grade laser treatments in order to prevent visual loss through unnecessary injury.