An Experimental Study On Dissolving And Detaching Vitreoretinal Interface With Enzymes

The posterior hyaloid surface of the vitreous gel is adherent to the inner retinal surface, most prominently at the vitreous base, optic disc, and along the major retinal vessels. The abnormal vitreoretinal junction plays a key role in the natural course of many vitreoretinal diseases. The total posterior vitr-eaous detachment (PVD) has a clear preventive effect on these diseases. It is benefit for the treatment of these vitreoretinal diseases to induce complete PVD reasonably. Pars plana vitrectomy provides a direct approach to release vitreous traction. However, surgical removal of the vitreous cortex is sometimes difficult and carries the risk of complications. According to the shortage of Pars plana vitrectomy and to analysis pharmacologic induction of PVD, we did this study in order to find a biochemical way that would separate vitreous fibres from the retinal surface to facilitate vitrectomy.Purpose: To investigate the safety dosage of intravitreal injection of Plasmin Hyaluronidase and their combination and to evaluate their efficacy in the production of posterior vitreous detachment(PVD) though animal experiments.Methods:After forty-eight New Zealand white rabbitswere examined using slit-lamp biomicroscopy ,+90D preset lens, indirect ophthalmoscope and electroretinograpy (ERG). Eight rabbits each were randomly assigned to one of six groups and one eye of each rabbit was experimental eye , the other is contrast eye. The position of drugs injection was in the posterior 1/3 of vitreous before papillary. The drug-injecting groups were assigned as followed: the first group-Hyaluronidase 20IU(0.1mlBSS), the second group-Hyaluronidase 30IU(0.1ml BSS), the third group-Plasmin lIU(0.1ml BSS), the forth group-Plasmin 2IU(0.1ml BSS), the fifth group-Plasmin 3IU(0.1ml BSS), the sixth group-Hyaluronidase 20IU(0.05ml BSS) combinated with Plasmin HU(0.05ml BSS) ; the contrast eyes were injected with BSS (0.1ml) at the same position. The rabbits were all followed for 2 weeks, and in this period all eyes were examined with slit-lamp biomicroscopy , +90 D preset lens ,indirect ophthalmoscope , electroretinography , B-scan , and optical coherence tomography(OCT) . After two weeks , the animals were killed and the eyes enucleated . Scan electron and light microscopy were performed.Results: Hyaluronidase concentration of 20IU or Plasmin concertration of 1 IU or their combination didn't produce inflammatory response and retinal toxicity in the eyes. 30IU Hyaluronidase and 2IU Plasmin both caused mild inflammatory response in the vitreous without retinalhistological changes , while the latter caused a reversible decrease in the ERG b-wave . 3IU of Plasmin caused severe inflammatory response with retinal histological and elecoretingraphic changes. In safty dosage neither Hyaluronidase nor Plasmin alone was successful in producing completely posterior vitreous detachment (PVD) , but the latter can produce partial PVD . The combination of Plasmin (1IU) and Hyaluronidase (20IU) was effective on producing completely posterior vitreous detachment without retinal toxicity.Conclusion: 1. 20IU of Hyaluronidase and 1IU of Plasmin are safe to retina and others structures in the eyes without any toxicity.2. Posterior vitreous injection of Hyaluronidase (20IU) combined with Plasmin (1IU) can produce complete posterior vitreous detachment.