Background Many ophthalmologists have proved that the intravitreal injection of plasmin can safely induce posterior vitreous detachment(PVD),but if it can generate the complete PVD need further to seek confirmation.Researches showed that the safe dose and toxicity dose of dispase are very near,so its application is limited.Whether hyaluronidase can induce PVD is still in controversy.Objective This study is to clarity the mechanism of pharmacological vitreolysis with plasmin and hyaluronidase.Methods Plasmin 4μmol/L,2μmol/L and 1μmol/L,plasmin 1μmol/L+ hyaluronidase 20μmol/L,hyaluronidase alone were intravitreally injected in lateral eye of 4 clean New Zealand white rabbits respectively,and 0.1mL BSS was injected as control group.Electron immunocytochemical technique was used to detect the laminin and fibronectin of interface between vitreous and retina in 7 days after intravitreal injection.Other 14 eyes of 7 clean New Zealand white rabbits were used in this study.Plasmin 1μmol/L + hyaluronidase 20μmol/L was intravitreally injected in the lateral eyes,and only plasmin 1μmol/L was injected in the fellow eyes.Plasmin activity in vitreous was evaluated in 15 and 30 minutes,1 hour,2,3,6,12 hours after intravitreal injection.The use of animals followed the Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Commission.Results The amounts of laminin and fibronectin in the vitreoretinal interface were decreased in 4μmol/L plasmin group,2μmol/L plasmin group,1μmol/L plasmin group,1μmol/L plasmin+20μmol/L hyaluronidase group compared with control group(P＜0.01).No significant difference was seen in the density of gold particles of anti FN between 20μmol/L hyaluronidase group and control group (P＞0.05).The change of amounts of fibronectin in the vitreoretinal interface was similar to that of laminin.Plasmin activity remained the highest level 1 hour after injection and thereafter gradually decreased and extincted in 12 hours and presented the same trend between plasmin 1μmol/L+hyaluronidase 20μmol/L group and only plasmin 1μmol/L group.Conclusion The mechanism of pharmacological vitreolysis is to dissolve laminin and fibronectin in the interface between vitreous and retina and therefore induce PVD.Combination of plasmin with hyaluronidase can increase the efficiency of pharmacological vitreolysis.The optimum selection of drug in inducing PVD should consider not only its role of lysis laminin and fibronectin but also the role of liquefying the vitreous.