An Experimental Study On Digesting And Detaching The Proliferative Membrane From The Retina In PVR With Enzymes

Proliferative vitreoretinopathy is the main cause of failure to rhegmatogenous retinal detachment surgery, and also the result of serious traumatic,vascular and inflammatory retinopathy. The foundation of pathoanatomical changes in PVR is the proliferative membrane, of which the vitreoretinal junction play a key role in the formation. Pas plana vitrectomy is the popular way to treat PVR now. But it's so difficult and dangerous to remove the proliferative membrane from the retina very clearly with mechanical means. Pharmacologic vitreolysis refers to intravitreal injection of agents that alter the molecular organization of vitreous to achieve posterior vitreous detachment. According to the main pathoanatomical changes in PVR , we proposed creatively the digesting and detaching the proliferative membrane from the retina in PVR with enzyme in order to find a way to facilitate vitrectomy of PVR.Purpose: To investigate the safety dosage and exposure time of intravitreal injection of t-PA,collagenase ,and to evaluate their efficacy in digesting and detaching theproliferative membrane from the retina in PVR, and to determine whether the degree of PVR can influence the efficacy of the drugs through animal experiments.Methods: Sixty adult colored-rabbits without any eye diseases were used as experimental animals. The animal model of PVR was induced in rabbits by intravitreal injection of fibroblast cells. One eye of each rabbit with PVR was used as experimental eye, the other as control eye with intravitreal injection of 0.1ml BSS. t-PA group: Twelve rabbits with PVR degree A were assigned randomly to two t-PA dosage groups: 12.5ug t-PA group and 25ug t-PA group. After determining the effective t-PA dosage (25ug t-PA), six experimented eyes with PVR degree B and six experimented eyes with PVR degree C were treated with 25ugt-PA. The eyes treated with t-PA were clinically observed for 7days.Collagenase group: Twenty-four rabbits with PVR degree A were randomly assigned to two collagenase-treating groups: 0.5IU with 1 hour exposure and 0.5IU with 12 hours exposure. After determining the appropriate treating group(0.5IU with 1 hour exposure)., six experimented eyes with PVR degree B and six experimented eyes with PVR degree C were treated with 0.5IU collagenase with 1 hour exposure. All experimental eyes were examined by slit-lamp,biomicroscopy,indirect ophthalmoscope,B-scan and electroretinography. After finishing clinical observation, the experimental eyes were enucleated to perform light microscopy,scan electron andtransmissing electromicrocope.Result: No inflammatory response and retinal toxicity were observed in the eyes treated with 12.5ugt-PA and 25ugt-PA.The eyes treated with 0.5IU collagenase with 1 hour exposure had light toxic response. The eyes treated with 0.5IU collagenase with 12 hours exposure had serious toxic reaction, such as cataract,retinal hemorrhage et al. 25ugt-PA group, 0.5IU collagenase with 1 hour exposure group and 0.5IU collagenase with 12 hours exposure group all can digest and detach the proliferative membrane from the retina in PVR effectively except 12.5ugt-PA group. With the higher degree of PVR, their efficiencies came down.Conclusion : 1 No inflammatory response and retinal toxic damage were produced in the eyes treated with 25ugt-PA with 1day exposure.The eyes treated with 0.5IU collagenase with 1 hour exposure had light toxic reaction.2 25ugt-PA with 1day exposure and 0.5IU collagenase with 1 hour exposure can digest and detach the proliferative membrane from the retina in PVR effectively, so can facilitate vitrectomy to treat PVR.3 With regard to the practicability in clinic, 25ugt-PA is better than 0.5IU collagenase with 1 hour exposure. The earlier we use the enzyme, the better effect we get.