Effect of intravitreal plasmin on vitreous removal through a 25-gauge cutting system in the rabbit in vivo

Purpose  Intravitreal plasmin creates a posterior vitreous detachment, but may also liquefy the vitreous. This study measures the rate of vitreous removal from rabbit eyes after plasmin injection in vivo. Methods  Intravitreal injections of 150 IU hyaluronidase (n = 5), 0.5 activity units (AU, n = 6) or 0.9 AU of streptokinase-activated human plasmin (n = four groups of 6) in 0.1 ml were performed in rabbits, the fellow eyes received 0.1 ml BSS. After 30 min (hyaluronidase), 30 min, 4 h, 12 h or 24 h (0.9 AU plasmin) or 24 h (0.5 AU plasmin), 1 ml of vitreous was removed from each eye without infusion, using a 25-gauge cutter and a standardized protocol. Animals were sacrificed after surgery. Results  Compared to fellow eyes, the average rate of vitreous removal was increased by hyaluronidase by 68.9 ± 6.3% (p < 0.05) and by 0.5 AU plasmin (24 h) by 26.8 ± 3.3% (p < 0.05). 0.9 AU of plasmin increased removal rates by 0.8 ± 10% (n.s.), 15.4 ± 6.3% (p < 0.05), 40.3 ± 3.1% (p < 0.05), and 71.9 ± 32.4% (p < 0.05) after 30 min, 4 h, 12 h and 24 h incubation respectively. The ratios of removal rates of treated/control eyes in the 0.9 AU groups showed a linear correlation with incubation time (r = 0.783, p < 0.0001). Conclusion  Intravitreal plasmin increases the rate of vitreous removal in rabbits. This work was presented in part at the 76th Annual Meeting of the Association for Research in Vision and Ophthalmology, 2004. Supported in part by grants from the University of Aachen, Germany and the Deutsche Forschungsgemeinschaft (HE 3503/1-1) to M. Hermel, and by NuVue Technologies, Keene, New Hampshire, USA. W. Dailey and M. Hartzer have a proprietary interest in plasmin.