Efficacy of plasmin enzymes and chondroitinase ABC in creating posterior vitreous separation in the pig: a masked,placebo-controlled in vivo study

Background Induction of posterior vitreous detachment (PVD) during vitrectomy helps to prevent proliferative complications, but can be traumatic to the retina, particularly in young patients. Adjunct enzymes have been proposed to facilitate PVD. We investigated the efficacy of enzymes in creating PVD as an adjunct to vitrectomy in the pig. Methods Five groups of 8 pigs received a masked intravitreal injection of chondroitinase (1 IU), human (0.4 or 1.3 activity units [AU]) or porcine plasmin (0.18 AU or 0.47 AU) into one eye, and osmolarity adjusted control into the other. After incubation, a core vitrectomy was performed on each eye at low suction, without vitreous peeling. The occurrence of spontaneous PVD and its extent were graded. Eyes were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Vitreous remnants on the retina were quantified in SEM. Data were analyzed using McNemar’s test for paired observations and Wilcoxon paired signed rank test. Results Spontaneous PVD occurred more frequently in human plasmin-treated eyes (p<0.025) and all plasmin eyes (p<0.025) than in placebo controls. The extent of PVD appeared larger in human plasmin (p<0.025) and all plasmin-treated eyes (p<0.025). In plasmin-treated eyes, SEM morphometry showed a significant reduction in the vitreous-covered retina areas. Chondroitinase failed to produce an effect. Conclusions Plasmin may prove a useful adjunct to conventional vitrectomy. The results were presented in part at the ARVO Annual Meeting, 2001.