[An experimental study on dissolving and detaching vitreoretinal interface with enzymes].
OBJECTIVE: To investigate the safety dosage of intravitreal injection of Plasmin, Hyaluronidase and their combination and to evaluate their efficacy in the formation of posterior vitreous detachment (PVD) through animal experiments. METHODS: Eight rabbits each were randomly assigned to one of six groups and one eye of each rabbit were experimental eye, the other is control eye. The position of drug injection was in posterior 1/3 of vitreous before papillary. The drug-injection groups were assigned as following: the first group-Hyaluronidase 20 IU (0.1 ml BSS), the second group-Hyaluronidase 30 IU (0.1 ml BSS), the third group-Plasmin 1 IU (0.1 ml BSS), the forth group-Plasmin 2 IU (0.1 ml BSS), the fifth group-Plasmin 3 IU (0.1 ml BSS), the sixth group- Hyaluronidase 20 IU (0.05 ml BSS) combined with Plasmin 1 IU (0.05 ml BSS); the control eyes were injected with BSS (0.1 ml) at the same position. The experimental rabbits were 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. After two weeks, the animals were killed and the eyes enucleated. Scan electron and light microscopy were performed. RESULTS: Hyaluronidase concentration of 20 IU, Plasmin concentration of 1 IU and their combination didn't produce inflammatory response and retinal toxicity in the experimental eyes. 30 IU Hyaluronidase and 2 IU Plasmin both caused mild inflammatory response in the vitreous without retinal histological changes, while the latter caused a reversible decrease in the ERG b-wave. 3 IU of Plasmin caused severe inflammatory response with retinal histological and electroretinographic changes. In safety dosage neither Hyaluronidase nor Plasmin alone were successful in producing completely posterior vitreous detachment (PVD), but the latter can produce partial PVD. The combination of Plasmin (1 IU) and Hyaluronidase (20 IU) was effective on producing completely PVD without retinal toxicity. CONCLUSION: 20 IU of Hyaluronidase and 1 IU of Plasmin are safe to retina and others structures in the eyes without any toxicity. Posterior vitreous injection of Hyaluronidase (20 IU) combined with Plasmin (1 IU) can produce complete posterior vitreous detachment.