Resolution of Experimental Intravitreal Fibrin by Tissue Plasminogen Activator

Intravitreal fibrin clots were produced by intravitreal injection of 0.2ml of autologous plasma in 62 rabbit eyes. The intravitreal injection of 0.25 μ g or more of tissue plasminogen activator(tPA) resulted in a total clearing of intravitreal fibrin within one day in all treated eyes. This was significantly faster than in the control eyes, in which complete clearing was not seen until 8 days later. This represents the plateau on the dose-response curve in doses ranging from 0.25 to 200 μ g. With light microscopy and transmission electron microscopy, retinal toxicity was demonstrated in eyes enucleated seven days after injection of 25 μ g or more of tPA. This study demonstrates that tPA was effective and safe at 12.5 μ g or less in clearing intravitreal fibrin in an experimental model. These results suggest that low dosages of tPA, probably of 3 μ g or less, may be useful in the treatment of severe postvitrectomy fibrin formation seen clinically.