OPTIMAL CONDITIONS REQUIRED FOR THE CREATION OF AN IATROGENIC CHORIORETINAL VENOUS ANASTOMOSIS IN THE DOG USING ARGON GREEN LASER PHOTOCOAGULATION

We have previously reported iatrogenic retinal to choroidal vein anast omosis, developed as a potential method of by-passing the site of obst ruction to venous outflow in retinal venous occlusion in dogs (1), and in rats (2). In order to minimise tissue damage to the retina and cho roid and increase the rate of success in these experiments, we investi gated in the dog model the factors that would promote an anastomosis a nd compare the effects of three different power levels. A small spot s ize (50 mu m) argon green laser beam of 514 nm at power levels of 0.5w , 1.5w and 2.5w were used. Spaced serial sections from each lesion wer e examined by light and by transmission electron microscopy. Morphomet ric measurements of the corresponding retinal pigment epithelium (RPE) /glial scar was computed using IBMPC digitising pad and sigma scan sof tware and the extent of tissue damage at the different power levels as sessed. At the lowest power level of 0.5w the damage to the retina was mild and there was an absence of anastomosis formation. At the 1.5w p ower level an anastomosis formed in 40% of the lesions. At the highest power level of 2.5w a 71% rate of success was obtained however, the d amage to the retina tended to the severe. The results of this study al so indicate that disruption of Bruch's membrane and vein rupture at th e time of irradiation are essential for anastomosis formation, which m ay be further enhanced by necrotic tissue, retinal pigment epithelial and glial scar formation and inflammation. These findings are useful i n establishing optimal conditions for the creation of a chorioretinal venous anastomosis, for consideration in human trials.